We are grateful to Dr. Magdalena G&#246;tz for her input during the development of this protocol. We thank Dr. Marius Wernig (Stanford University) for generously providing us with the sox2 coding sequence. We are also very grateful to Dr. Alexandra Lepier for virus production. This work was supported by grants of the Deutsche Forschungsgemeinschaft (BE 4182/2-2) and the BMBF (01GN1009A) to B.B., and the Bavarian State Ministry of Sciences, Research and the Arts to M.K. and B.B. C.S. received funding from the binational SYSTHER-INREMOS Virtual Institute (German and Slovenian Federal Ministries of Education and Research) and the DFG (SFB 824).

1. Isolation and Culturing of Adult Human Brain Cells
Experiments involving human tissue should be performed in accordance with all relevant governmental and institutional regulations regarding the use of human material for research purposes. The present protocol was developed in accordance with the approval by the ethical committee of the Medical Faculty of the LMU Munich and written informed consent from all patients.
This protocol of preparing cultures of the human adult cerebral cortex has been established using specimen of patients of both sexes suffering from temporal lobe epilepsy or other deep-seated non-traumatic, non-malignant lesions. The tissue obtained from the surgical room comprised exclusively the access channel to the brain lesion and therefore is considered healthy. The age range of the patients was 19-70 years.
<ol>
	<li>Prepare growth medium by adding heat-inactivated fetal calf serum (FCS) to DMEM high glucose with GlutaMAX to obtain a final concentration of 20% FCS. Add 5 ml penicillin/streptomycin to a total of 500 ml growth medium. Perform this and all subsequent steps requiring sterile culture conditions in an appropriate laminar flow hood.</li>
	<li>Keep the adult human brain biopsy obtained from the surgical room in Hanks&#8217; balanced salt solution with CaCl2 and MgCl2 (HBSS) medium including HEPES (10 mM final concentration) on ice until processing. Start processing as soon as possible.</li>
	<li>To start the dissociation into single cells, transfer the tissue into a 65 mm petri dish and mince into small pieces by using two sterile single-use scalpels. For enzymatic digestion use 3-6 ml TrypLE in a 15 ml conical tube and incubate for 15-30 min at 37 &#176;C in a water bath.</li>
	<li>Add 1 volume of prewarmed growth medium to facilitate dissociation and gently triturate the solution containing tissue pieces up and down by first using a 5 ml disposable pipette, followed by using a glass Pasteur pipette until homogenization of the cell suspension. Typically, some residual tissue pieces, mostly consisting of white matter, will remain in the suspension.</li>
	<li>Spin down at 157 x g for 5 min and resuspend the pellet in the appropriate amount of growth medium (10 ml per uncoated T75 culture flask). Use one T75 culture flask for a biopsy of 5-10 mm diameter in size and extrapolate from this in case of larger specimens.</li>
	<li>Place cells into a 37 &#176;C incubator with 5% CO2 and 5% O2.</li>
	<li>Replace half of the medium every 3-4 days until cells have reached confluency. This usually takes up to two weeks (referred to as passage 0 [P0]).</li>
</ol>
2. In vitro Expansion and Characterization of Adult Human Brain Cells
<ol>
	<li>In vitro expansion:
	<ol>
		<li>Aspirate the culture medium and wash with phosphate-buffered saline (PBS), kept at room temperature, before adding 3 ml TrypLE.</li>
		<li>Incubate at 37 &#176;C for 5-10 min until most of the cells detached. Gently tap the flasks to facilitate lifting of the cells; following addition of 3 volumes of growth medium, transfer the cells into a 15 ml conical tube and spin down at 157 x g for 5 min and resuspend the cells in the appropriate amount of growth medium.</li>
		<li>Passage the cells at a ratio of 1:3 for optimal yield into new T75 cell culture flasks. 
		Note: We have passaged these cells until P5 without any signs of reduced reprogramming efficiency. While at P0 the culture contains a considerable fraction of endothelial cells (as assessed by CD34 expression), at subsequent passages their number becomes negligible.</li>
	</ol>
	</li>
	<li>Characterization of adult human brain cultures:
	<ol>
		<li>Immunocytochemistry:
		<ol>
			<li>For characterization of the cells, seed ~60,000 cells onto poly-D-lysine-coated glass cover slips in 500 &#956;l fresh growth medium in 24-well tissue culture plates and incubate at 37 &#176;C with 5% CO2 and 5% O2.</li>
			<li>For immunocytochemical analysis of the cultured human brain cells remove the medium and wash 3x&#160;with 1 ml of PBS.</li>
			<li>Fix cells by adding 500 &#956;l of 4% paraformaldehyde in PBS for 15 min at room temperature.</li>
			<li>Transfer the glass cover slips into an appropriate humidified staining chamber and block with 80 &#956;l PBS containing 3% bovine serum albumin (BSA) and 0.5% Triton X-100 for 1 hr at room temperature.</li>
			<li>Add primary antibodies diluted in the same solution (for dilution factors see table of specific reagents and equipment) and incubate overnight at 4 &#176;C or 1 hr at room temperature. 
			Note: A substantial but varying fraction of the cells at this stage of culturing are immunoreactive for platelet-derived growth factor receptor &#946; (PDGFR&#946;), cluster of differentiation 146 (CD146), NG2 chondroitin sulfate proteoglycan, and smooth muscle actin (SMA), i.e. markers characteristic of microvessel-associated pericytes. Only a minority (&#60;1%) express the astroglial markers glial fibrillary acidic protein (GFAP) and S100&#946;. Furthermore, at this stage the culture should be devoid of any cells expressing the neuronal marker &#946;III-tubulin. Use multiple primary antibody combinations for co-labeling of different markers. Further confirmation of the expression of glial, neuronal, endothelial and pericyte markers can be obtained by reverse transcription and quantitative real time polymerase chain reaction (not described in this protocol).</li>
			<li>Following incubation with the primary antibodies wash three times with 1 ml PBS and add the corresponding secondary antibodies (in the appropriate dilutions) to the staining solution and incubate 1 hr at room temperature in the dark. Wash the cells 3x&#160;with PBS. If required, prior to mounting include staining with DAPI for 5 min at room temperature.</li>
			<li>Use antifading mounting medium and analyze the cover slips using an epifluorescence microscope or a confocal microscope.</li>
		</ol>
		</li>
		<li>Flow cytometry:
		<ol>
			<li>For analysis of surface marker expression using flow cytometry, grow cells to confluency in uncoated T25 or T75 cell culture flasks.</li>
			<li>Detach cells by using TrypLE as described before and resuspend in staining solution consisting of PBS + 0.5% BSA. Per staining reaction, resuspend 100,000-200,000 cells in 100 &#956;l of staining solution. Prepare single staining reactions per antibody used (CD146-FITC, CD140b-PE, CD34-APC, CD13-FITC, respective isotype control antibodies).</li>
			<li>Add fluorochrome-conjugated antibodies to each staining solution (for dilutions see table of specific reagents and equipment) directly into the cell suspension and incubate at 4 &#176;C for 30 min in the dark.</li>
			<li>Wash the cells three times with 500 &#956;l PBS and spin down between each washing step at 157 x g for 5 min.</li>
			<li>Resuspend the cell pellet in 0.5-1 ml staining solution and transfer cells through a cell strainer (70 &#956;m) to FACS tubes. Protect the sample from exposure to light.</li>
			<li>Vortex samples prior to placing them in the FACS instrument.</li>
			<li>To analyze the living cells and exclude debris and cell aggregates, gate for FSC-A and SSC-A. Cell duplets are specifically gated out by FSC-A and FSC-W. To determine the right gating conditions for the cell surface markers set the gates with isotype-matched antibody control conjugated to the respective fluorochrome. Then determine the proportion of antibody-bound cells.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3. Enrichment for Pericyte-derived Cells by Fluorescence Activated Cell Sorting
<ol>
	<li>Purify the pericyte cell population (resuspended in growth medium) prior to transduction via FACS sorting using a 70 &#956;m nozzle. Use CD34-APC in combination with CD140b-PE and CD146-FITC to select for pericytes. Sort for CD34-negative, CD140b-, and CD146-positive cells.</li>
	<li>Collect the sorted cells in growth medium and plate onto poly-D-lysine-coated glass cover slips in 24-well tissue culture plates and incubate at 37 &#176;C with 5% CO2 and 5% O2.</li>
	<li>48 h after sorting replace the medium with fresh growth medium and perform transduction as described in &#160;Protocol&#160;4.</li>
</ol>
4. Retroviral Transduction of Pericyte-derived Cells and Reprogramming into Induced Neurons
Note: Refer to local biosafety guidelines when handling retroviral particles. In Germany the use of the retroviruses employed here require biosafety level 2. For production of retroviral particles refer to protocol6. For retroviral constructs used for reprogramming, refer to Karow et al. (2012). Retroviruses were pseudotyped with VSV-G (vesicular stomatitis virus-glycoprotein)5. For production please refer to Gavrilescu&#160;et al6.
<ol>
	<li>24 hr prior to retroviral transduction seed ~60,000 cells onto poly-D-lysine-coated glass cover slips in 500 &#956;l fresh growth medium in 24-well tissue culture plates and incubate at 37 &#176;C with 5% CO2 and 5% O2.</li>
	<li>The next day, replace the growth medium with 500 &#956;l fresh, prewarmed growth medium and add 1 &#956;l of the respective concentrated supernatants containing retroviral particles (pCAG-IRES-dsred for control, especially during establishing the protocol in the lab), pCAG-ascl1-IRES-dsred, pCAG-sox2-IRES-gfp.</li>
	<li>One day later, remove the medium including the viral particles from the cells and add 1 ml fresh, prewarmed B27-differentiation medium, composed of 49 ml DMEM high glucose with GlutaMAX and 1 ml B27 serum-free supplement. Maintain the cells in culture at 37 &#176;C in 5% CO2 and 5% O2 for 4-8 weeks without changing the medium as repetitive medium changes become harmful as iNs mature.</li>
</ol>
5. Characterization of Induced Neurons by Immunocytochemistry
<ol>
	<li>To determine the cellular identity of the transduced cells, in particular to demonstrate the acquisition of a neuronal phenotype, perform immunocytochemistry against neuronal antigens such as bIII-tubulin, MAP2, and NeuN (for antibodies and their respective dilutions, see table of specific reagents and equipment; follow the same procedure as indicated in 2.2.1).</li>
	<li>For improving the maturation of PdiNs, co-culture these cells with neurons derived from E14 mouse cerebral cortices. To this end, dissect the cerebral cortex and dissociate the tissue mechanically with a fire-polished glass Pasteur pipette. Add 10,000-50,000 murine neurons to cultures of pericyte-derived cells 2-3 weeks following transduction with sox2- and ascl1-encoding retroviruses and continue culturing. Transduced cells can be distinguished from murine neurons by their reporter (GFP and dsRed) expression, either by live epifluorescence or following immunocytochemistry for GFP and dsRed.</li>
	<li>To assess the formation of synapses onto PdiNs by murine neurons, perform immunocytochemistry against vesicular neurotransmitter receptors such as vesicular glutamate transporter 1 (vGluT1).</li>
	<li>Probe transduced cells for their electrical properties (i.e. ability of generating action potentials) and the establishment of functional synapses by patch-clamp electrophysiology. For details of the procedure see Heinrich et al. (2011).</li>
</ol>

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Authors have nothing to disclose.

The present protocol describes the in vitro expansion and enrichment of pericyte-derived cells following isolation from the adult human cerebral cortex and the subsequent conversion into iNs by retrovirus-mediated expression of the neurogenic transcription factors Sox2 and Ascl1. Such protocol provides an experimental in vitro system to study the lineage-conversion of brain-resident cells into neurons and potentially also glia, with the goal in mind to ultimately translate this direct conversion approac...

As opposed to reprogramming of somatic cells into induced pluripotent stem cells (iPSCs), which in turn are endowed with a plethora of differentiation potentials, direct reprogramming aims for straight conversion of one specific cell type into another. With respect to their application in the context of disease modeling and potential cell-based therapies, both reprogramming approaches have specific advantages and disadvantages. Reprogramming into iPSCs (i) provides a virtually infinite source of cells; (ii) allows for genetic engineering; (iii) endows with a nearly unlimited differentiation potential. However, major disadvantages of iPSCs entail the risk of tumorigenicity of the undifferentiated cells (teratoma formation in vivo) and the need for ex vivo cultivation and subsequent transplantation if these cells are to be used for cell-based therapies. Conversely, direct lineage-reprogramming is restricted by the lower yield of the desired cells which correlates directly with the number of the targeted cells of the starting population, but possesses the advantage that lineage-reprogrammed cells appear to exhibit no tumorigenic risk upon transplantation1,2; furthermore, direct reprogramming can even be achieved in situ, i.e. within the organ where these cells would be required, thus avoiding the need of transplantation.
With this in mind, our lab has pursued the possibility of lineage-reprogramming brain-resident cells into iNs as a novel approach towards cell-based therapies of neurodegenerative diseases. Brain-resident cells that may be potentially considered as cellular targets for lineage-reprogramming comprise different types of macroglia (astrocytes, NG2 cells and oligodendrocytes), microglia, and microvessel-associated cells (endothelial cells and pericytes). We have extensively studied the in vitro reprogramming potential of astroglia of the cerebral cortex of early postnatal mice3-5. In search of similarly suitable cell sources for direct lineage-reprogramming in the adult human brain, we encountered a cell population that can be successfully reprogrammed into iNs and exhibit hallmarks of pericytes. Here we describe a protocol of how to harvest these cells from adult human brain biopsies, to expand and enrich these cells in vitro, and finally successfully reprogram a substantial fraction of these in vitro expanded cells (in the range of 25-30%) into iNs. Reprogramming can be achieved by simultaneous retrovirus-mediated co-expression of two transcription factors, sox2 and ascl1. These PdiNs were found to acquire the ability of repetitive action potential firing and to serve as synaptic targets for other neurons indicating their capability of integrating into neural networks. Our protocol provides a straightforward procedure for the isolation and lineage conversion of adult human brain pericytes into iNs.

<table border="0" cellpadding="0" cellspacing="0" width="320">
	<tbody>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">anti-CD140b-PE</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">558821</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-CD146-FITC</td>
			<td style="width:80px;">AbD Serotec</td>
			<td style="width:80px;">MCA2141FT</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-CD13-FITC</td>
			<td style="width:80px;">AbD Serotec</td>
			<td style="width:80px;">MVA1270A488T</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">anti-CD34-APC</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">560940</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-PDGFR&#946;</td>
			<td style="width:80px;">Cell Signaling</td>
			<td style="width:80px;">3169S</td>
			<td style="width:80px;">use 1:200</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">anti-CD146</td>
			<td style="width:80px;">Abcam</td>
			<td style="width:80px;">Ab75769</td>
			<td style="width:80px;">use 1:400</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">anti-NG2</td>
			<td style="width:80px;">Millipore</td>
			<td style="width:80px;">AB5320</td>
			<td style="width:80px;">use 1:400</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-SMA</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">A2547</td>
			<td style="width:80px;">use 1:400</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-&#946;III-tubulin</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">T8660</td>
			<td style="width:80px;">use 1:400</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-MAP2</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">M4403</td>
			<td style="width:80px;">use 1:200</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-GFAP</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">G3893</td>
			<td style="width:80px;">use 1:600</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">anti-GFP</td>
			<td style="width:80px;">Aves Labs</td>
			<td style="width:80px;">GFP 10-20</td>
			<td style="width:80px;">use 1:1000</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">anti-RFP</td>
			<td style="width:80px;">Chromotek</td>
			<td style="width:80px;">5F8</td>
			<td style="width:80px;">use 1:500</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-S100&#946;</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">S2532</td>
			<td style="width:80px;">use 1:300</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">anti-NeuN</td>
			<td style="width:80px;">Millipore</td>
			<td style="width:80px;">MAB377</td>
			<td style="width:80px;">use 1:200</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-GABA</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">A2052</td>
			<td style="width:80px;">use 1:500</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-Calretinin</td>
			<td style="width:80px;">Millipore</td>
			<td style="width:80px;">AB5054</td>
			<td style="width:80px;">use 1:500</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">anti-vGluT1</td>
			<td style="width:80px;">SYnaptic SYstems</td>
			<td style="width:80px;">135511</td>
			<td style="width:80px;">use 1:1000</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Rat IgG1 isotype control FITC</td>
			<td style="width:80px;">AbD Serotec</td>
			<td style="width:80px;">11-4301-81</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Rat IgG1 isotype control PE</td>
			<td style="width:80px;">AbD Serotec</td>
			<td style="width:80px;">12-4301-81</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Rat IgG1 isotype control APC</td>
			<td style="width:80px;">AbD Serotec</td>
			<td style="width:80px;">17-4301-81</td>
			<td style="width:80px;">use 1:100</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:80px;">TrypLE</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">12605-010</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">DMEM, high glucose, GlutaMAX</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">61965</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">B27 serum-free supplement</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">17504044</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:80px;">fetal calf serum</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">10106-169</td>
			<td style="width:80px;">perform heat inactivation by incubation at 56 &#176;C for 30 min</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Penicillin-Streptomycin</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">15140122</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:80px;">HBSS (Hanks Balanced Salt Solution)</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">24020-091</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="198">
			<td height="198" style="height:198px;width:80px;">Dulbecco&#39;s PBS without CaCl2 and MgCl2 (D-PBS, 1&#215;; Invitrogen, cat. no. 14190)</td>
			<td style="width:80px;">Invitrogen</td>
			<td style="width:80px;">14190</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">HEPES&#160;</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">H3375</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Poly-D-lysine hydrobromide (PDL)</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">P0899</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">PFA (paraformaldehyde)</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">P1648</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Bovine serum albumin</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">A9418</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">Triton X-100</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">T9284</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:80px;">DAPI (4&#8242;,6-Diamidin-2-phenylindole) dilactate</td>
			<td style="width:80px;">Sigma-Aldrich</td>
			<td style="width:80px;">042M4005</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Aqua-Poly/Mount</td>
			<td style="width:80px;">Polysciences</td>
			<td style="width:80px;">18606-20</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Polypropylene round-bottom tubes&#160;</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">352063</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:80px;">Polystyrene round-bottom tubes with cell-strainer cap&#160;</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">352235</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">24-well plates</td>
			<td style="width:80px;">Orange Scientific</td>
			<td style="width:80px;">5530305</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:80px;">75 cm2 culture flasks</td>
			<td style="width:80px;">Greiner Bio-One</td>
			<td style="width:80px;">658175</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:80px;">25 cm2 culture flasks</td>
			<td style="width:80px;">Greiner Bio-One</td>
			<td style="width:80px;">690175</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Disposable pipettes 10 ml</td>
			<td style="width:80px;">Sarstedt</td>
			<td align="center" style="width:80px;">#########</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Glass Pasteur pipettes (150 mm)</td>
			<td style="width:80px;">Fisherbrand</td>
			<td style="width:80px;">FB50251</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Glass coverslips 12 mm diameter</td>
			<td style="width:80px;">Menzel</td>
			<td style="width:80px;">CB00120RA1</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Surgical disposable scalpels&#160;</td>
			<td style="width:80px;">B. Braun</td>
			<td style="width:80px;">5518083</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Tissue culture dishes&#160;</td>
			<td style="width:80px;">Greiner Bio-One</td>
			<td style="width:80px;">633180</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Conical tubes 15ml</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">352095</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:80px;">Laminar flow hood</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="169">
			<td height="169" style="height:169px;width:80px;">Centrifuge and swing-out rotor with adapters for 15 ml and 50 ml tubes</td>
			<td style="width:80px;">Hettich Lab Technology</td>
			<td style="width:80px;">1406</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:80px;">Flow cytometry cell sorter: FACSAria l with FACSDiva software&#160;</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Humified cell culture incubator</td>
			<td style="width:80px;">Eppendorf Galaxy 170R</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Wather bath at 37 &#176;C</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">FACSFlow sheath fluid&#160;</td>
			<td style="width:80px;">BD Biosciences</td>
			<td style="width:80px;">342003</td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:80px;">Epifluorescence microscope BX61</td>
			<td style="width:80px;">Olympus</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:80px;">Confocal microscope LSM710</td>
			<td style="width:80px;">Zeiss</td>
			<td style="width:80px;"></td>
			<td style="width:80px;"></td>
		</tr>
	</tbody>
</table>

lineage-reprogramming of pericyte-derived cells of the adult human brain into induced neurons

Direct lineage-reprogramming of non-neuronal cells into induced neurons (iNs) may provide insights into the molecular mechanisms underlying neurogenesis and enable new strategies for in vitro modeling or repairing the diseased brain. Identifying brain-resident non-neuronal cell types amenable to direct conversion into iNs might allow for launching such an approach in situ, i.e. within the damaged brain tissue. Here we describe a protocol developed in the attempt of identifying cells derived from the adult human brain that fulfill this premise. This protocol involves: (1) the culturing of human cells from the cerebral cortex obtained from adult human brain biopsies; (2) the in vitro expansion (approximately requiring 2-4 weeks) and characterization of the culture by immunocytochemistry and flow cytometry; (3) the enrichment by fluorescence-activated cell sorting (FACS) using anti-PDGF receptor-&#946; and anti-CD146 antibodies; (4) the retrovirus-mediated transduction with the neurogenic transcription factors sox2 and ascl1; (5) and finally the characterization of the resultant pericyte-derived induced neurons (PdiNs) by immunocytochemistry (14 days to 8 weeks following retroviral transduction). At this stage, iNs can be probed for their electrical properties by patch-clamp recording. This protocol provides a highly reproducible procedure for the in vitro lineage conversion of brain-resident pericytes into functional human iNs.

The first outcome of this protocol after successfully establishing a culture from a specimen of human adult cerebral cortex consists in the identification of the cellular composition of the culture. Immunocytochemistry for cell type specific proteins reveals a considerable degree of heterogeneity between cultures derived from specimen of different patients (Figure 1A). As quantified by flow cytometry there is always a substantial fraction of cells that express PDGFR&#946; (on average ~75%, ranging from 3...

Watch this Scientific Journal Video about Lineage-reprogramming of Pericyte-derived Cells of the Adult Human Brain into Induced Neurons at JoVE.com

Lineage-reprogramming of Pericyte-derived Cells of the Adult Human Brain into Induced Neurons

Targeting brain-resident cells for direct lineage-reprogramming offers new perspectives for brain repair. Here we describe a protocol of how to prepare cultures enriched for brain-resident pericytes from the adult human cerebral cortex and convert these into induced neurons by retrovirus-mediated expression of the transcription factors Sox2 and Ascl1.

Direct lineage-reprogramming of non-neuronal cells into induced neurons (iNs) may provide insights into the molecular mechanisms underlying neurogenesis ...

lineage-reprogramming-pericyte-derived-cells-adult-human-brain-into

Research

JoVE Journal

Neuroscience

12.2K Views.  Ludwig Maximilians University Munich. Targeting brain-resident cells for direct lineage-reprogramming offers new perspectives for brain repair. Here we describe a protocol of how to prepare cultures enriched for brain-resident pericytes from the adult human cerebral cortex and convert these into induced neurons by retrovirus-mediated expression of the transcription factors Sox2 and Ascl1.

Video: Lineage-reprogramming of Pericyte-derived Cells of the Adult Human Brain into Induced Neurons

Studying the Integration of Adult-born Neurons

Neurogenesis occurs in adult mammalian brains in the sub-ventricular zone (SVZ) of the lateral ventricle and in the sub-granular zone (SGZ) of the hippocampal dentate gyrus throughout life. Previous reports have shown that adult hippocampal neurogenesis is associated with diverse brain disorders, including epilepsy, schizophrenia, depression and anxiety (1). Deciphering the process of normal and aberrant adult-born neuron integration may shed light on the etiology of these diseases and inform the development of new therapies.
SGZ adult neurogenesis mirrors embryonic and post-natal neuronal development, including stages of fate specification, migration, synaptic integration, and maturation. However, full integration occurs over a prolonged, 6-week period. Initial synaptic input to adult-born SGZ dentate granule cells (DGCs) is GABAergic, followed by glutamatergic input at 14 days (2). The specific factors which regulate circuit formation of adult-born neurons in the dentate gyrus are currently unknown.
Our laboratory uses a replication-deficient retroviral vector based on the Moloney murine leukemia virus to deliver fluorescent proteins and hypothesized regulatory genes to these proliferating cells. This viral technique provides high specificity and resolution for analysis of cell birth date, lineage, morphology, and synaptogenesis.
A typical experiment often employs two or three viruses containing unique label, transgene, and promoter elements for single-cell analysis of a desired developmental process in vivo. The following protocol describes a method for analyzing functional newborn neuron integration using a single green (GFP) or red (dTomato) fluorescent protein retrovirus and patch-clamp electrophysiology.

A way to study the integration of newborn dentate granule cells in adult animals is described. This technique uses an engineered retrovirus to label newborn neurons, followed by electrophysiological recordings to determine in vivo functional integration.

Neurogenesis occurs in adult mammalian brains in the sub-ventricular zone (SVZ) of the lateral ventricle and in the sub-granular zone (SGZ) of the ...

The Specification of Telencephalic Glutamatergic Neurons from Human Pluripotent Stem Cells

Here, a stepwise procedure for efficiently generating telencephalic glutamatergic neurons from human pluripotent stem cells (PSCs) has been described. The differentiation process is initiated by breaking the human PSCs into clumps which round up to form aggregates when the cells are placed in a suspension culture. The aggregates are then grown in hESC medium from days 1-4 to allow for spontaneous differentiation. During this time, the cells have the capacity to become any of the three germ layers. From days 5-8, the cells are placed in a neural induction medium to push them into the neural lineage. Around day 8, the cells are allowed to attach onto 6 well plates and differentiate during which time the neuroepithelial cells form. These neuroepithelial cells can be isolated at day 17. The cells can then be kept as neurospheres until they are ready to be plated onto coverslips. Using a basic medium without any caudalizing factors, neuroepithelial cells are specified into telencephalic precursors, which can then be further differentiated into dorsal telencephalic progenitors and glutamatergic neurons efficiently. Overall, our system provides a tool to generate human glutamatergic neurons for researchers to study the development of these neurons and the diseases which affect them.

This procedure yields telencephalic neurons by going through checkpoints which are similar to those observed during human development. The cells are allowed to spontaneously differentiate, are exposed to factors which push them towards the neural lineage, are isolated, and are plated onto coverslips to allow for terminal differentiation and maturation.

Here, a stepwise procedure for efficiently generating telencephalic glutamatergic neurons from human pluripotent stem cells (PSCs) has been described. The ...

Derivation of Adult Human Fibroblasts and their Direct Conversion into Expandable Neural Progenitor Cells

Generation of&#160;induced pluripotent stem cell (iPSCs) from adult skin fibroblasts and subsequent differentiation into somatic cells provides fascinating prospects for the derivation of autologous transplants that circumvent histocompatibility barriers. However, progression through a pluripotent state and subsequent complete differentiation into desired lineages remains a roadblock for the clinical translation of iPSC technology because of the associated neoplastic potential and genomic instability. Recently, we and others showed that somatic cells cannot only be converted into iPSCs but also into different types of multipotent somatic stem cells by using defined factors, thereby circumventing progression through the pluripotent state. In particular, the direct conversion of human fibroblasts into induced neural progenitor cells (iNPCs) heralds the possibility of a novel autologous cell source for various applications such as cell replacement, disease modeling and drug screening. Here, we describe the isolation of adult human primary fibroblasts by skin biopsy and their efficient direct conversion into iNPCs by timely restricted expression of Oct4, Sox2, Klf4, as well as c-Myc. Sox2-positive neuroepithelial colonies appear after 17 days of induction and iNPC lines can be established efficiently by monoclonal isolation and expansion. Precise adjustment of viral multiplicity of infection and supplementation of leukemia inhibitory factor during the induction phase represent critical factors to achieve conversion efficiencies of up to 0.2%. Thus far, patient-specific iNPC lines could be expanded for more than 12 passages and uniformly display morphological and molecular features of neural stem/progenitor cells, such as the expression of Nestin and Sox2. The iNPC lines can be differentiated into neurons and astrocytes as judged by staining against TUJ1 and GFAP, respectively. In conclusion, we report a robust protocol for the derivation and direct conversion of human fibroblasts into stably expandable neural progenitor cells that might provide a cellular source for biomedical applications such as autologous neural cell replacement and disease modeling.

Generation of induced pluripotent stem cells provides fascinating prospects for the derivation of autologous transplants. However, progression through a pluripotent state and laborious re-differentiation still hinders clinical translation. Here we describe the derivation of adult human fibroblasts and their direct conversion into induced neural progenitor cells and the subsequent differentiation into neural lineages.

Generation of&#160;induced pluripotent stem cell (iPSCs) from adult skin fibroblasts and subsequent differentiation into somatic cells provides ...

Simple Generation of a High Yield Culture of Induced Neurons from Human Adult Skin Fibroblasts

Induced neurons (iNs), the product of somatic cells directly converted to neurons, are a way to obtain patient-derived neurons from tissue that is easily accessible. Through this route, mature neurons can be obtained in a matter of a few weeks. Here, we describe a straightforward and rapid one-step protocol to obtain iNs from dermal fibroblasts obtained through biopsy samples from adult human donors. We explain each step of the process, including the maintenance of the dermal fibroblasts, the freezing procedure to build a stock of the cell line, seeding of the cells for reprogramming, as well as the culture conditions during the conversion process. In addition, we describe the preparation of glass coverslips for electrophysiological recordings, long-term coating conditions, and fluorescence activated cell sorting (FACS). We also illustrate examples of the results to be expected. The protocol described here is easy to perform and can be applied to human fibroblasts derived from human skin biopsies from patients with various different diagnoses and ages. This protocol generates a sufficient amount of iNs which can be used for a wide array of biomedical applications, including disease modeling, drug screening, and target validation.

Direct neuronal reprogramming generates neurons that maintain the age of the starting somatic cell. Here, we describe a single vector-based method to generate induced neurons from dermal fibroblasts obtained from adult human donors.

Induced neurons (iNs), the product of somatic cells directly converted to neurons, are a way to obtain patient-derived neurons from tissue that is easily ...

Conversion of Human Induced Pluripotent Stem Cells (iPSCs) into Functional Spinal and Cranial Motor Neurons Using PiggyBac Vectors

We describe here a method to obtain functional spinal and cranial motor neurons from human induced pluripotent stem cells (iPSCs). Direct conversion into motor neuron is obtained by ectopic expression of alternative modules of transcription factors, namely Ngn2, Isl1 and Lhx3 (NIL) or Ngn2, Isl1 and Phox2a (NIP). NIL and NIP specify, respectively, spinal and cranial motor neuron identity. Our protocol starts with the generation of modified iPSC lines in which NIL or NIP are stably integrated in the genome via a piggyBac transposon vector. Expression of the transgenes is then induced by doxycycline and leads, in 5 days, to the conversion of iPSCs into MN progenitors. Subsequent maturation, for 7 days, leads to homogeneous populations of spinal or cranial MNs. Our method holds several advantages over previous protocols: it is extremely rapid and simplified; it does not require viral infection or further MN isolation; it allows generating different MN subpopulations (spinal and cranial) with a remarkable degree of maturation, as demonstrated by the ability to fire trains of action potentials. Moreover, a large number of motor neurons can be obtained without purification from mixed populations. iPSC-derived spinal and cranial motor neurons can be used for in vitro modeling of Amyotrophic Lateral Sclerosis and other neurodegenerative diseases of the motor neuron. Homogeneous motor neuron populations might represent an important resource for cell type specific drug screenings.

Conversion of Human Induced Pluripotent Stem Cells iPSCs into Functional Spinal and Cranial Motor Neurons Using PiggyBac Vectors

This protocol allows rapid and efficient conversion of induced pluripotent stem cells into motor neurons with a spinal or cranial identity, by ectopic expression of transcription factors from inducible piggyBac vectors.

We describe here a method to obtain functional spinal and cranial motor neurons from human induced pluripotent stem cells (iPSCs). Direct conversion into ...

Short-Term Free-Floating Slice Cultures from the Adult Human Brain

Organotypic, or slice cultures, have been widely employed to model aspects of the central nervous system functioning in vitro. Despite the potential of slice cultures in neuroscience, studies using adult nervous tissue to prepare such cultures are still scarce, particularly those from human subjects. The use of adult human tissue to prepare slice cultures is particularly attractive to enhance the understanding of human neuropathologies, as they hold unique properties typical of the mature human brain lacking in slices produced from rodent (usually neonatal) nervous tissue. This protocol describes how to use brain tissue collected from living human donors submitted to resective brain surgery to prepare short-term, free-floating slice cultures. Procedures to maintain and perform biochemical and cell biology assays using these cultures are also presented. Representative results demonstrate that the typical human cortical lamination is preserved in slices after 4 days in vitro (DIV4), with expected presence of the main neural cell types. Moreover, slices at DIV4 undergo robust cell death when challenged with a toxic stimulus (H2O2), indicating the potential of this model to serve as a platform in cell death assays. This method, a simpler and cost-effective alternative to the widely used protocol using membrane inserts, is mainly recommended for running short-term assays aimed to unravel mechanisms of neurodegeneration behind age-associated brain diseases. Finally, although the protocol is devoted to using cortical tissue collected from patients submitted to surgical treatment of pharmacoresistant temporal lobe epilepsy, it is argued that tissue collected from other brain regions/conditions should also be considered as sources to produce similar free-floating slice cultures.

A protocol to prepare free-floating slice cultures from adult human brain is presented. The protocol is a variation of the widely used slice culture method using membrane inserts. It is simple, cost-effective, and recommended for running short-term assays aimed to unravel mechanisms of neurodegeneration behind age-associated brain diseases.

Organotypic, or slice cultures, have been widely employed to model aspects of the central nervous system functioning in vitro. Despite the potential of ...

Migration, Chemo-Attraction, and Co-Culture Assays for Human Stem Cell-Derived Endothelial Cells and GABAergic Neurons

Role of brain vasculature in nervous system development and etiology of brain disorders is increasingly gaining attention. Our recent studies have identified a special population of vascular cells, the periventricular endothelial cells, that play a critical role in the migration and distribution of forebrain GABAergic interneurons during embryonic development. This, coupled with their cell-autonomous functions, alludes to novel roles of periventricular endothelial cells in the pathology of neuropsychiatric disorders like schizophrenia, epilepsy, and autism. Here, we have described three different in vitro assays that collectively evaluate the functions of periventricular endothelial cells and their interaction with GABAergic interneurons. Use of these assays, particularly in a human context, will allow us to identify the link between periventricular endothelial cells and brain disorders. These assays are simple, low cost, and reproducible, and can be easily adapted to any adherent cell type.

We present three simple in vitro assays-the long-distance migration assay, the co-culture migration assay, and chemo-attraction assay-that collectively evaluate the functions of human stem cell derived periventricular endothelial cells and their interaction with GABAergic interneurons.

Role of brain vasculature in nervous system development and etiology of brain disorders is increasingly gaining attention. Our recent studies have ...

Obtaining Human Microglia from Adult Human Brain Tissue

Microglia are resident innate immune cells of the central nervous system (CNS). Microglia play a critical role during development, in maintaining homeostasis, and during infection or injury. Several independent research groups have highlighted the central role that microglia play in autoimmune diseases, autoinflammatory syndromes and cancers. The activation of microglia in some neurological diseases may directly participate in pathogenic processes. Primary microglia are a powerful tool to understand the immune responses in the brain, cell-cell interactions and dysregulated microglia phenotypes in disease. Primary microglia mimic in vivo microglial properties better than immortalized microglial cell lines. Human adult microglia exhibit distinct properties as compared to human fetal and rodent microglia. This protocol provides an efficient method for isolation of primary microglia from adult human brain. Studying these microglia can provide critical insights into cell-cell interactions between microglia and other resident cellular populations in the CNS including, oligodendrocytes, neurons and astrocytes. Additionally, microglia from different human brains may be cultured for characterization of unique immune responses for personalized medicine and a myriad of therapeutic applications.

This protocol is an efficient, cost effective and robust method of isolating primary microglia from live, adult, human brain tissue. Isolated primary human microglia can serve as a tool for studying cellular processes in homeostasis and disease.

Microglia are resident innate immune cells of the central nervous system (CNS). Microglia play a critical role during development, in maintaining ...

Derivation, Expansion, Cryopreservation and Characterization of Brain Microvascular Endothelial Cells from Human Induced Pluripotent Stem Cells

Brain microvascular endothelial cells (BMECs) can be differentiated from human induced pluripotent stem cells (iPSCs) to develop ex vivo cellular models for studying blood-brain barrier (BBB) function. This modified protocol provides detailed steps to derive, expand, and cryopreserve BMECs from human iPSCs using a different donor and reagents than those reported in previous protocols. iPSCs are treated with essential 6 medium for 4 days, followed by 2 days of human endothelial serum-free culture medium supplemented with basic fibroblast growth factor, retinoic acid, and B27 supplement. At day 6, cells are sub-cultured onto a collagen/fibronectin matrix for 2 days. Immunocytochemistry is performed at day 8 for BMEC marker analysis using CLDN5, OCLN, TJP1, PECAM1, and SLC2A1. Western blotting is performed to confirm BMEC marker expression, and absence of SOX17, an endodermal marker. Angiogenic potential is demonstrated with a sprouting assay. Trans-endothelial electrical resistance (TEER) is measured using chopstick electrodes and voltohmmeter starting at day 7. Efflux transporter activity for ATP binding cassette subfamily B member 1 and ATP binding cassette subfamily C member 1 is measured using a multi-plate reader at day 8. Successful derivation of BMECs is confirmed by the presence of relevant cell markers, low levels of SOX17, angiogenic potential, transporter activity, and TEER values ~2000 &#937; x cm2. BMECs are expanded until day 10 before passaging onto freshly coated collagen/fibronectin plates or cryopreserved. This protocol demonstrates that iPSC-derived BMECs can be expanded and passaged at least once. However, lower TEER values and poorer localization of BMEC markers was observed after cryopreservation. BMECs can be utilized in co-culture experiments with other cell types (neurons, glia, pericytes), in three-dimensional brain models (organ-chip and hydrogel), for vascularization of brain organoids, and for studying BBB dysfunction in neuropsychiatric disorders.

This protocol details an adapted method to derive, expand, and cryopreserve brain microvascular endothelial cells obtained by differentiating human induced pluripotent stem cells, and to study blood brain barrier properties in an ex vivo model.

Brain microvascular endothelial cells (BMECs) can be differentiated from human induced pluripotent stem cells (iPSCs) to develop ex vivo cellular models ...

Generation of Human Neurons and Oligodendrocytes from Pluripotent Stem Cells for Modeling Neuron-Oligodendrocyte Interactions

In Alzheimer&#8217;s disease (AD) and other neurodegenerative disorders, oligodendroglial failure is a common early pathological feature, but how it contributes to disease development and progression, particularly in the gray matter of the brain, remains largely unknown. The dysfunction of oligodendrocyte lineage cells is hallmarked by deficiencies in myelination and impaired self-renewal of oligodendrocyte precursor cells (OPCs). These two defects are caused at least in part by the disruption of interactions between neuron and oligodendrocytes along the buildup of pathology. OPCs give rise to myelinating oligodendrocytes during CNS development. In the mature brain cortex, OPCs are the major proliferative cells (comprising ~5% of total brain cells) and control new myelin formation in a neural activity-dependent manner. Such neuron-to-oligodendrocyte communications are significantly understudied, especially in the context of neurodegenerative conditions such as AD, due to the lack of appropriate tools. In recent years, our group and others have made significant progress to improve currently available protocols to generate functional neurons and oligodendrocytes individually from human pluripotent stem cells. In this manuscript, we describe our optimized procedures, including the establishment of a co-culture system to model the neuron-oligodendrocyte connections. Our illustrative results suggest an unexpected contribution from OPCs/oligodendrocytes to the brain amyloidosis and synapse integrity and highlight the utility of this methodology for AD research. This reductionist approach is a powerful tool to dissect the specific hetero-cellular interactions out of the inherent complexity inside the brain. The protocols we describe here are expected to facilitate future studies on oligodendroglial defects in the pathogenesis of neurodegeneration.

The neuron-glial interactions in neurodegeneration are not well understood due to inadequate tools and methods. Here, we describe optimized protocols to obtain induced neurons, oligodendrocyte precursor cells, and oligodendrocytes from human pluripotent stem cells and provide examples of the values of these methods in understanding cell-type-specific contributions in Alzheimer&#8217;s disease.

In Alzheimer&#8217;s disease (AD) and other neurodegenerative disorders, oligodendroglial failure is a common early pathological feature, but how it ...