Work was supported by grants from the Smith Family Foundation (B.S.), Dana Foundation (B.S.), John Merck Scholars Program (B.S.), NINDS (RO1-NS-07100801; B.S.), NRSA (F32-NS-066698; D.P.S.), Nancy Lurie Marks Foundation (D.P.S.), NIH (P30-HD-18655; MRDDRC Imaging Core).

1. Anterograde Labeling of RGC Presynaptic Inputs
Note: All experiments involving the use of animals were reviewed and overseen by the institutional animal care and use committee (IACUC) in accordance with all NIH guidelines.
<ol>
	<li>Sterilize field and instruments.</li>
	<li>Anesthetize mouse with 4 vol % isoflurane in a Plexiglas induction chamber (this vol % isoflurane works for neonatal-adult mice). Observe mice closely to avoid over-anesthetizing. CAUTION: Avoid inhalation with a vacu...

<ol>
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No conflicts of interest declared.

In order to accurately measure phagocytosis, engulfed material must be labeled in such a way that the researcher can visualize it once lysosomal degradation has occurred. In addition, high resolution imaging is required, followed by the use of software that will enable the researcher to visualize the volume of the entire cell and quantify its contents. In this protocol, we describe a highly reliable and quantitative method for measuring phagocyte-mediated engulfment using CTB conjugated to Alexa dyes to label engulfed ma...

Synaptic circuits remodel throughout the life of an animal. In the developing brain, synapses form in excess and must undergo synaptic pruning which involves the selective removal of a subset of synapses and the maintenance and strengthening of those synapses that remain8-10. This process is necessary to achieve the precise connectivity characteristic of the adult nervous system. In the adult, synapses can also be plastic, particularly in the context of learning and memory. The structural correlates of this plasticity are thought to include the addition and/or elimination of dendritic spines and presynaptic boutons11-13. In addition to these roles in the healthy nervous system, synaptic remodeling is also involved in nervous system disease/injury12,14,15. For example, following spinal cord injury, severed axons must subsequently remodel and form new synapses to achieve functional recovery16-19.
Emerging as an important aspect of synaptic plasticity is the process of phagocytosis or engulfment of synapses destined for removal3,5,20. We recently showed this phenomenon in the context of synaptic pruning in the healthy, postnatal mouse brain7. Specifically, microglia, the resident CNS immune cells and phagocytes, were shown to engulf presynaptic inputs during a peak period and in a region of developmental synaptic pruning, the postnatal dorsal lateral geniculate nucleus (dLGN) of the thalamus. Genetic or pharmacological blockade of this engulfment resulted in sustained deficits in synaptic connectivity.
In this protocol, we describe a reliable and highly quantitative assay to measure phagocyte-mediated engulfment of presynaptic inputs. For the purposes of this article, this assay will be presented in the context of the developing retinogeniculate system, which includes retinal ganglion cells (RGCs) residing in the retina that project presynaptic inputs to the dLGN (Figure 1A). To begin, a lysosomal degradation-resistant anterograde labeling strategy will be described, which is used to visualize RGC-specific presynaptic inputs in the dLGN (Figure 1)7,21. Following this description, a detailed methodology for imaging and quantitatively measuring engulfment using confocal microscopy combined with 3 dimensional (3D) surface volume rendering will be given. This methodology is based on fixed tissue preparation but may also be adapted for use in live imaging studies. Importantly, while the assay has been validated in the context of the healthy, postnatal retinogeniculate system, one could apply the same techniques to assess other phagocyte-neuron interactions throughout the brain and during disease, as well as phagocyte function in other organ systems.

<table border="0" cellpadding="0" cellspacing="0" width="533">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:144px;">Heat pad</td>
			<td style="width:159px;">Vet Equip, Inc.</td>
			<td style="width:168px;">965500&#160;</td>
			<td style="width:63px;"></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:144px;">Warm water source for heat pad</td>
			<td style="width:159px;">Kent Scientific</td>
			<td style="width:168px;">TP-700</td>
			<td></td>
		</tr>
		<tr height="39">
			<td height="39" style="height:39px;width:144px;">Stereo microscope</td>
			<td style="width:159px;">DSC Optical</td>
			<td style="width:168px;">Zeiss Opmi -6 Surgical Microscope</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="40" rowspan="2" style="height:40px;width:144px;">Sliding microtome with freezing stage</td>
			<td rowspan="2" style="width:159px;">Leica</td>
			<td rowspan="2" style="width:168px;">SM2010 R</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:144px;">Microtome blade</td>
			<td style="width:159px;">Leica</td>
			<td style="width:168px;">14021607100</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:144px;">Fluorescent dissecting microscope</td>
			<td style="width:159px;">Nikon</td>
			<td style="width:168px;">SMZ800 with Epi-fluorescence attachment</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:144px;">Spinning disk confocal microscope</td>
			<td style="width:159px;">Perkin Elmer</td>
			<td style="width:168px;">UltraView Vox Spinning Disk Confocal</td>
			<td></td>
		</tr>
		<tr height="51">
			<td height="51" style="height:51px;width:131px;">10 &#181;l Hamilton gas tight syringes</td>
			<td style="width:131px;">Hamilton</td>
			<td style="width:116px;">80030</td>
			<td style="width:144px;">Use a different syringe for each color dye/tracer</td>
		</tr>
		<tr height="51">
			<td height="51" style="height:51px;width:131px;">Hamilton needles</td>
			<td style="width:131px;">Hamilton</td>
			<td style="width:116px;">7803-05, specifications: blunt, 1.5&#34;</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="20">
			<td height="54" rowspan="3" style="height:54px;width:131px;">Alexa-conjugated cholera toxin &#946; subunit (CTB)</td>
			<td rowspan="3" style="width:131px;">Invitrogen</td>
			<td style="width:116px;">488: C22841</td>
			<td rowspan="3" style="width:144px;">Reconstitute in sterile saline, 80 &#181;l (488), 100 &#181;l (594), 20 &#181;l (647)</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:116px;">594: C22842</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:116px;">647: C34778</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Phosphate Buffered Saline&#160;(PBS)</td>
			<td style="width:131px;">Sigma</td>
			<td>P4417-50TAB</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="73">
			<td height="73" style="height:73px;width:131px;">Neomycin and Polymyxin B Sulfates and Bacitracin Zinc Ophthalmic Ointment USP (antibiotic ointment)</td>
			<td style="width:131px;">Bausch &#38; Lomb</td>
			<td style="width:116px;">24208-780-55</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:131px;">30.5 gauge needle</td>
			<td style="width:131px;">Becton Dickinson</td>
			<td style="width:116px;">305106</td>
			<td rowspan="3" style="width:144px;"></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:131px;">Spring scissors</td>
			<td style="width:131px;">Roboz</td>
			<td style="width:116px;">RS-5630</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Cotton-tipped applicator</td>
			<td style="width:131px;">Fisher</td>
			<td style="width:116px;">23-400-125</td>
		</tr>
		<tr height="21">
			<td height="104" rowspan="2" style="height:104px;width:131px;">Paraformaldeyde (PFA)</td>
			<td rowspan="2" style="width:131px;">Electron Microscopy Sciences</td>
			<td rowspan="2" style="width:116px;">15710</td>
			<td rowspan="2" style="width:144px;">Dilute 16%to 4% in PBS. Paraformaldehye is toxic, use&#160; in a fume hood and wear personal protective equipment.</td>
		</tr>
		<tr height="83">
		</tr>
		<tr height="36">
			<td height="138" rowspan="4" style="height:138px;width:131px;">Dissection tools &#8211; scissors, forceps, spatula</td>
			<td style="width:131px;">Small scissors: Fine Science Tools</td>
			<td style="width:116px;">Small scissors:14370-22</td>
			<td rowspan="4" style="width:144px;"></td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Large scissors: Roboz</td>
			<td style="width:116px;">Large scissors: RS-6820</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">#55 forceps: Fine Science Tools</td>
			<td style="width:116px;">#55 forceps: 11255-20</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Spatula: Ted Pella, Inc.</td>
			<td style="width:116px;">Spatula: 13504</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:131px;">Sucrose</td>
			<td style="width:131px;">Sigma</td>
			<td style="width:116px;">S8501-5KG</td>
			<td style="width:144px;">Make 30% sucrose in PBS (weight/vol)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:131px;">OCT Compound</td>
			<td style="width:131px;">VWR</td>
			<td style="width:116px;">25608-930</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:131px;">Weigh boat</td>
			<td style="width:131px;">USA Scientific</td>
			<td style="width:116px;">2347-1426</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:131px;">24-well plates</td>
			<td style="width:131px;">BD Biosciences</td>
			<td style="width:116px;">353047</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="87">
			<td height="87" style="height:87px;width:131px;">Sodium phosphate monobasic</td>
			<td style="width:131px;">Sigma</td>
			<td style="width:116px;">S6566-500G</td>
			<td rowspan="2" style="width:144px;">Make 0.2 M sodium phosphate monobasic (PB-A) in ddH20 and 0.2 M sodium phosphate dibasic (PB-B) in ddH20.&#160; To make 0.1 M PB, combine 19 ml PB-A and 81 ml PB-B, fill to 200 ml with ddH20&#160;&#160;</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:131px;">Sodium phosphate dibasic&#160;</td>
			<td style="width:131px;">Sigma</td>
			<td>S5136-500G</td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Coverslips, 22 X 50 mm, No. 1.5</td>
			<td style="width:131px;">VWR</td>
			<td style="width:116px;">48393 194</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:131px;">Charged microscope slide</td>
			<td style="width:131px;">VWR</td>
			<td style="width:116px;">48311-703</td>
			<td style="width:144px;"></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:131px;">Vectasheild</td>
			<td style="width:131px;">Vector Laboratories</td>
			<td style="width:116px;">H-1200</td>
			<td style="width:144px;"></td>
		</tr>
	</tbody>
</table>

an engulfment assay: a protocol to assess interactions between cns phagocytes and neurons

Phagocytosis is a process in which a cell engulfs material (entire cell, parts of a cell, debris, etc.) in its surrounding extracellular environment and subsequently digests this material, commonly through lysosomal degradation. Microglia are the resident immune cells of the central nervous system (CNS) whose phagocytic function has been described in a broad range of conditions from neurodegenerative disease (e.g., beta-amyloid clearance in Alzheimer&#8217;s disease) to development of the healthy brain (e.g., synaptic pruning)1-6. The following protocol is an engulfment assay developed to visualize and quantify microglia-mediated engulfment of presynaptic inputs in the developing mouse retinogeniculate system7. While this assay was used to assess microglia function in this particular context, a similar approach may be used to assess other phagocytes throughout the brain (e.g., astrocytes) and the rest of the body (e.g., peripheral macrophages) as well as other contexts in which synaptic remodeling occurs (e.g. ,brain injury/disease).

Recently, we used this engulfment assay to visualize and quantify microglia-mediated engulfment of presynaptic inputs in the developing retinogeniculate system (Figure 1)7. RGCs from CX3CR1-EGFP heterozygous mice were anterogradely traced with CTB-594 and CTB-647 into the left and right eyes, respectively. Following this tracing, EGFP-positive microglia within the dLGN were imaged. These images were subsequently surface-rendered for volume measurements.
Using this t...

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An Engulfment Assay: A Protocol to Assess Interactions Between CNS Phagocytes and Neurons

Microglia are the resident immune cells of the central nervous system (CNS) with a high capacity to phagocytose or engulf material in their extracellular environment. Here, a broadly applicable, reliable, and highly quantitative assay for visualizing and measuring microglia-mediated engulfment of synaptic components is described.

Phagocytosis is a process in which a cell engulfs material (entire cell, parts of a cell, debris, etc.) in its surrounding extracellular environment and ...

an-engulfment-assay-protocol-to-assess-interactions-between-cns

Research

JoVE Journal

Neuroscience

18.0K visualizações.  Boston Children's Hospital, Harvard Medical School.  Microglia são as células do sistema imunológico residentes do sistema nervoso central (SNC), com uma elevada capacidade de fagocitar ou engolir o material no seu ambiente extracelular. Aqui, um ensaio amplamente aplicável, confiável e altamente quantitativa para visualizar e medir engulfment mediada por microglia de componentes sinápticas é descrito. 