This work was supported by the Austrian Science Fund Project P29110-B21, the &#8220;Hochschuljubil&#228;umsstiftung der Stadt Wien zur F&#246;rderung der Wissenschaft&#8221; Project H-3065/2011, the European Fund for Regional Development (EFRE, IWB2020), the Federal State of Upper Austria, and the &#8220;Land O&#214; Basisfinanzierung&#8221;.

<ol>
	<li>Vickers, K. C., Palmisano, B. T., Shoucri, B. M., Shamburek, R. D., Remaley, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroRNAs+are+transported+in+plasma+and+delivered+to+recipient+cells+by+high-density+lipoproteins.">MicroRNAs are transported in plasma and delivered to recipient cells by high-density lipoproteins.</a> Nature Cell Biology. 13 (4), 423-435 (2011).</li><li>Tabet, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HDL-transferred+microRNA-223+regulates+ICAM-1+expression+in+endothelial+cells.">HDL-transferred microRNA-223 regulates ICAM-1 expression in endothelial cells.</a> Nature Communications. 5, (2014).</li><li>Wahid, F., Shehzad, A., Khan, T., Kim, Y. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroRNAs:+Synthesis,+mechanism,+function,+and+recent+clinical+trials.">MicroRNAs: Synthesis, mechanism, function, and recent clinical trials.</a> Biochimica et Biophysica Acta - Molecular Cell Research. 1803 (11), 1231-1243 (2010).</li><li>Carthew, R. W., Sontheimer, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Origins+and+Mechanisms+of+miRNAs+and+siRNAs.">Origins and Mechanisms of miRNAs and siRNAs.</a> Cell. 136 (4), 642-655 (2009).</li><li>Fabian, M. R., Sonenberg, N., Filipowicz, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+mRNA+Translation+and+Stability+by+microRNAs.">Regulation of mRNA Translation and Stability by microRNAs.</a> Annual Review of Biochemistry. 79 (1), 351-379 (2010).</li><li>Filipowicz, W., Bhattacharyya, S. N., Sonenberg, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+post-transcriptional+regulation+by+microRNAs:+Are+the+answers+in+sight?.">Mechanisms of post-transcriptional regulation by microRNAs: Are the answers in sight?.</a> Nature Reviews Genetics. 9 (2), 102-114 (2008).</li><li>Jonas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstitution+of+High-Density+Lipoproteins.">Reconstitution of High-Density Lipoproteins.</a> Methods in Enzymology. , 553-582 (1986).</li><li>Ando, T., Uchihashi, T., Kodera, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Speed+AFM+and+Applications+to+Biomolecular+Systems.">High-Speed AFM and Applications to Biomolecular Systems.</a> Annual Review of Biophysics. 42 (1), 393-414 (2013).</li><li>Bustin, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+MIQE+Guidelines:+Minimum+Information+for+Publication+of+Quantitative+Real-Time+PCR+Experiments.">The MIQE Guidelines: Minimum Information for Publication of Quantitative Real-Time PCR Experiments.</a> Clinical Chemistry. 55 (4), 611-622 (2009).</li><li>Patsch, J. R., Patsch, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zonal+ultracentrifugation.">Zonal ultracentrifugation.</a> Methods in Enzymology. 129 (1966), 3-26 (1986).</li><li>Bradford, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+rapid+and+sensitive+method+for+the+quantitation+of+microgram+quantities+of+protein+utilizing+the+principle+of+protein-dye+binding.">A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding.</a> Analytical Biochemistry. 72 (1-2), 248-254 (1976).</li><li>Yamamoto, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Speed+Atomic+Force+Microscopy+Techniques+for+Observing+Dynamic+Biomolecular+Processes.">High-Speed Atomic Force Microscopy Techniques for Observing Dynamic Biomolecular Processes.</a> Methods in Enzymology. 475, 541-564 (2010).</li><li>Stangl, H., Cao, G., Wyne, K. L., Hobbs, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scavenger+receptor,+class+B,+type+I-dependent+stimulation+of+cholesterol+esterification+by+high+density+lipoproteins,+low+density+lipoproteins,+and+nonlipoprotein+cholesterol.">Scavenger receptor, class B, type I-dependent stimulation of cholesterol esterification by high density lipoproteins, low density lipoproteins, and nonlipoprotein cholesterol.</a> Journal of Biological Chemistry. 273 (47), 31002-31008 (1998).</li><li>Hochberg, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+the+False+Discovery+Rate:+a+Practical+and+Powerful+Approach+to+Multiple+Testing.">Controlling the False Discovery Rate: a Practical and Powerful Approach to Multiple Testing.</a> Journal of the Royal Statistical Society. 57 (1), 289-300 (1995).</li><li>Mestdagh, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+and+universal+method+for+microRNA+RT-qPCR+data+normalization.">A novel and universal method for microRNA RT-qPCR data normalization.</a> Genome Biology. 10 (6), (2009).</li><li>Schumaker, V. N., Puppione, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=6]+Sequential+Flotation+Ultracentrifugation.">6] Sequential Flotation Ultracentrifugation.</a> Methods in Enzymology. 128 (C), 155-170 (1986).</li><li>Wagner, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+levels+and+cellular+transfer+of+circulating+lipoprotein-bound+microRNAs.">Characterization of levels and cellular transfer of circulating lipoprotein-bound microRNAs.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 33 (6), 1392-1400 (2013).</li><li>Meier, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+chronic+kidney+disease+on+macrophage+cholesterol+efflux.">Effect of chronic kidney disease on macrophage cholesterol efflux.</a> Life Sciences. 136, 1-6 (2015).</li><li>Axmann, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serum+and+Lipoprotein+Particle+miRNA+Profile+in+Uremia+Patients.">Serum and Lipoprotein Particle miRNA Profile in Uremia Patients.</a> Genes. 9 (11), 533 (2018).</li></ol>

The authors have nothing to disclose.

Here, the isolation of lipoprotein particle fractions from human blood and the determination of their individual miRNA content is described step-by-step. It is critical to work in an RNase-free environment while handling isolated and synthesized miRNA&#8212;particle-embedded miRNA is obviously sheltered from enzymatic degradation. As the miRNA/particle ratio of native lipoprotein particles is rather low, artificial enrichment with miRNA is required to study the holo particle uptake of cells. Thereby, the reconstitution of HDL particles as described previously7 is modified to incorporate miRNA strands. Additionally, the separation of the lipid and protein fraction during this procedure allows scientists to examine lipid- and protein-associated components of the lipoprotein particle19. In a similar way, the labeling procedure of LDL particles is adapted. Interestingly, the addition of spermine&#8212;a natural stabilizer of nucleotides&#8212;did not influence the miRNA/particle ratio. It should be noted that, in principle, the method allows the infolding of other substances than miRNA within a lipoprotein particle. Of course, there is a limit with regard to the physical size of the substance based on the overall size of HDL (diameter: 5-12 nm) and LDL particles (diameter: 18-25 nm).
Concerning the quality control of reconstituted/labeled lipoprotein particles, HS-AFM is an applicable method to characterize HDL/LDL particles at the single particle level. In comparison to EM, it allows for shorter preparation times and near-physiological conditions (wet, room temperature).
Due to its inherent sensitivity and amplification, qPCR is the method of choice to detect low miRNA concentrations. Alternatively, single-molecule sensitive fluorescence microscopy, which is able to detect even individual molecules, would not be suitable due to the low concentrations of, for instance, fluorescently labeled miRNA strands per particle. Thus, the ratio of miRNA strands per native lipoprotein particle has been found to be 10-8. Artificial enrichment increases the ratio by a factor of 10,000, which facilitates the estimation of the cellular lipoprotein uptake rate (no significant difference is detected using native lipoprotein particles 19). The high sensitivity of qPCR makes it possible to determine this uptake rate by measuring the number of miRNA strands after the incubation time and the miRNA/particle ratio. It should be noted that the calculated value ignores cellular degradation and release of miRNA and, thus, represents at least a lower limit for the lipoprotein particle uptake ratio.
In the future, the method can be adapted to transfer pharmaceutical substances (notably also lipophilic ones) in cells and correlate their biological effect to the intracellular concentration (determined via the uptake rate of lipoprotein particles).

Lipoprotein particles are composed of a monolayer of amphiphilic lipids and cholesterol enclosing a core of cholesteryl esters and triglyceride fats. The whole particle is stabilized by membrane-embedded apolipoproteins, which define the particle&#8217;s biological functionality. Lipoprotein particles can be distinguished according to their respective increasing density and, thus, decreasing size, namely as very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), LDL, and HDL particles. Despite the transportation of water-insoluble components in the bloodstream, it has been demonstrated that HDL particles carry noncoding strands of miRNA1,2. Micro-RNAs are a class of short (usually two dozen nucleotides) RNA strands, which degrade intracellularly complementary mRNA strands and, thereby, alter the expression profile of certain proteins3,4,5,6. Furthermore, alterations of the miRNA profile have been found in a variety of diseases and, thus, the profile is applicable as a biomarker for diagnosis and prognosis. The extracellular transport of miRNAs between cells via lipoprotein particles may serve as an additional mechanism for intercellular mRNA level modulation. To quantitatively estimate the biological effect, knowledge regarding the absolute and relative miRNA content of lipoprotein particles is needed.
Quantitative real-time PCR is a suitable and relatively quick method to gain this information. Hence, the relative quantification (RQ) value can be calculated, and relative differences between different samples and lipoprotein fractions are estimable. Multiwell microfluidic array cards are a fast and easy-to-use method to determine the relative presence (equates to the RQ value) of miRNAs in a sample. Multiwell microfluidic array cards consist of 96 or 384 individual reaction chambers for individual qPCR reactions embedded in a microfluidic device. Each chamber contains the required hydrolysis probe and specific qPCR primers for one individual miRNA. The advantages are a short handling time due to standardization, a simple workflow, and a reduced number of pipetting steps. Moreover, the required sample volume is minimized. In contrast to the relative quantification, the absolute miRNA content requires a comparison of qPCR sample results with standard curves of known absolute numbers of miRNA strands. It should be noted that, due to their relatively low miRNA content, standard and, moreover, even single-molecule sensitive imaging techniques are not feasible&#8212;the artificial enrichment of lipoprotein particles with miRNA is inevitable to study cellular lipoprotein particle interaction and miRNA transfer. Regarding this, delipidation of the HDL particle followed with subsequent relipidation7 allows the incorporation of and, thus, enrichment with miRNA strands. Similar enrichment of LDL particles with miRNA is not feasible due to the hydrophobicity of the apoB-100 protein, which is the main constituent of the LDL particle. However, by addition of the polar solvent dimethyl sulfoxide (DMSO), which is able to penetrate lipid membranes, LDL particles can be artificially loaded with miRNA strands as well.
High-speed atomic force microscopy (HS-AFM) is a powerful tool for the characterization of biological specimens offering subnanometer spatial and subsecond temporal resolution8. Hence, it is a well-suited technique for the quality control of modified lipoprotein particles as native/reconstituted/labeled lipoprotein particles can be imaged under a near-physiological environment.
Here, a qPCR-based protocol is presented step-by-step to determine the absolute/relative miRNA content of lipoprotein particles and cell samples, which allows an estimation of the cellular lipoprotein particle uptake rate. Moreover, a method for the enrichment of lipoprotein particles with miRNA is demonstrated. This method may be adapted for the general manipulation of lipoprotein content and, hence, demonstrates the applicability of lipoprotein particles as targets for drug delivery.

<table>
	<tbody>
		<tr>
			<td>Ultracentrifuge</td>
			<td>Beckman</td>
			<td>Optima L-100 XP</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Ultracentrifuge rotor</td>
			<td>Beckman</td>
			<td>TI 55.2</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Vacutainer (EDTA)</td>
			<td>Becton Dickinson</td>
			<td>366643</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Kaliumbromid</td>
			<td>Sigma Aldrich</td>
			<td>2110</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Ultracentrifuge tubes</td>
			<td>Beckman</td>
			<td>342414</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Ultracentrifuge tube sealer</td>
			<td>Beckman</td>
			<td>342428</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Sodiumchlorid</td>
			<td>Carl Roth GmbH</td>
			<td>P029.2</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Fisher Scientific</td>
			<td>D/0650/50</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>Dialysis tubes, MWCO 12 - 14k</td>
			<td>Spectra</td>
			<td>132700</td>
			<td>Lipoprotein isolation</td>
		</tr>
		<tr>
			<td>synthetic miRNA</td>
			<td>microSynth</td>
			<td>-</td>
			<td>synthetic miRNA</td>
		</tr>
		<tr>
			<td>TRIS buffer pH 7</td>
			<td>Ambion</td>
			<td>AM9850G</td>
			<td>synthetic miRNA</td>
		</tr>
		<tr>
			<td>TRIS buffer pH 8</td>
			<td>Ambion</td>
			<td>AM9855G</td>
			<td>synthetic miRNA</td>
		</tr>
		<tr>
			<td>sterile tubes</td>
			<td>Carl Roth GmbH</td>
			<td>ENE8.1</td>
			<td>synthetic miRNA</td>
		</tr>
		<tr>
			<td>Photometer</td>
			<td>Eppendorf</td>
			<td>Eppendorf Biophotometer</td>
			<td>Bradford assay</td>
		</tr>
		<tr>
			<td>Cuvette</td>
			<td>Carl Roth GmbH</td>
			<td>XK20</td>
			<td>Bradford assay</td>
		</tr>
		<tr>
			<td>Coomassie G-250 Stain</td>
			<td>BioRad GmbH</td>
			<td>161-0786</td>
			<td>Bradford assay</td>
		</tr>
		<tr>
			<td>Sodiumchlorid</td>
			<td>Carl Roth GmbH</td>
			<td>3957.1</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Fluka Analytical</td>
			<td>03690-100ML</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>TRIS buffer pH 8.0</td>
			<td>Ambion</td>
			<td>AM9855G</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>Ethanol 100%</td>
			<td>AustrAlco</td>
			<td>Ethanol Absolut 99.9%</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>Diethyl ether</td>
			<td>Carl Roth GmbH</td>
			<td>3942.1</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Thermo Scientific</td>
			<td>Multifuge X3R</td>
			<td>Delipitation</td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Carl Roth GmbH</td>
			<td>3313.1</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Carl Roth GmbH</td>
			<td>4627.1</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Phosphatidylcholine</td>
			<td>Sigma Aldrich GmbH</td>
			<td>P3556-25mg</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Cholesterol oleate</td>
			<td>Sigma Aldrich GmbH</td>
			<td>C-9253-250mg</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>cholesterol</td>
			<td>Sigma Aldrich GmbH</td>
			<td>C8667-500mg</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>glass tubes</td>
			<td>Carl Roth GmbH</td>
			<td>K226.1</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>spermine</td>
			<td>Sigma Aldrich GmbH</td>
			<td>S3256-1G</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Thermomixer</td>
			<td>Eppendorf</td>
			<td>Thermomixer comfort</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Sodium deoxycholate</td>
			<td>Sigma Aldrich GmbH</td>
			<td>3097-25G</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>Magnetic stir bar</td>
			<td>Carl Roth GmbH</td>
			<td>0955.2</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>100&#181;L micropipettes</td>
			<td>Carl Roth GmbH</td>
			<td>A762.1</td>
			<td>Reconstitution</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Carl Roth GmbH</td>
			<td>9143.2</td>
			<td>Dialysis</td>
		</tr>
		<tr>
			<td>Amberlite XAD-2 beads</td>
			<td>Sigma Aldrich GmbH</td>
			<td>10357</td>
			<td>Dialysis</td>
		</tr>
		<tr>
			<td>Slide-A-Lyzer casette (cut-off 20 kDa)</td>
			<td>Thermo Scientific</td>
			<td>66003</td>
			<td>Dialysis</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>Braun</td>
			<td>9161406V</td>
			<td>Dialysis</td>
		</tr>
		<tr>
			<td>Syringe needle</td>
			<td>Braun</td>
			<td>465 76 83</td>
			<td>Dialysis</td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Carl Roth GmbH</td>
			<td>3054.2</td>
			<td>Labeling of LDL particles</td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>life technologies</td>
			<td>D12345</td>
			<td>Labeling of LDL particles</td>
		</tr>
		<tr>
			<td>Atomic Force Microscope</td>
			<td>RIBM</td>
			<td>SS-NEX</td>
			<td>Quality control of reconstituted/labeled lipoprotein particles</td>
		</tr>
		<tr>
			<td>Muscovite Mica (V-1 Grade)</td>
			<td>Christine Gr&#246;pl</td>
			<td>G250-1/V1</td>
			<td>Quality control of reconstituted/labeled lipoprotein particles</td>
		</tr>
		<tr>
			<td>AFM Cantilever</td>
			<td>Nanoworld</td>
			<td>USC-F1.2-k0.15</td>
			<td>Quality control of reconstituted/labeled lipoprotein particles</td>
		</tr>
		<tr>
			<td>Gwyddion 2.49</td>
			<td>Czech Metrology Institute</td>
			<td>http://gwyddion.net</td>
			<td>Quality control of reconstituted/labeled lipoprotein particles</td>
		</tr>
		<tr>
			<td>Chamber slides, Nunc Lab-Tek</td>
			<td>VWR</td>
			<td>734-2122</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>HBSS</td>
			<td>Carl Roth GmbH</td>
			<td>9117.1</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>Cell counter</td>
			<td>Omni Life Science GmbH</td>
			<td>Casy</td>
			<td>Cell culture</td>
		</tr>
		<tr>
			<td>miRNeasy Mini Kit</td>
			<td>QIAGEN</td>
			<td>217004</td>
			<td>miRNA extraction</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5415R</td>
			<td>miRNA extraction</td>
		</tr>
		<tr>
			<td>20G needle</td>
			<td>Braun</td>
			<td>Sterican 465 75 19</td>
			<td>miRNA extraction</td>
		</tr>
		<tr>
			<td>5ml syringe</td>
			<td>Becton Dickinson</td>
			<td>309050</td>
			<td>miRNA extraction</td>
		</tr>
		<tr>
			<td>PCR cabinet</td>
			<td>Esco</td>
			<td>PCR-3A1</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>TaqMan Reverse Transcription Kit</td>
			<td>Thermo Scientific</td>
			<td>4366596</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>Rnase-free water</td>
			<td>Carl Roth GmbH</td>
			<td>T143</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>0.2 ml tubes</td>
			<td>Brand</td>
			<td>781305</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Carl Roth GmbH</td>
			<td>Microcentrifuge AL</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>Thermocycler</td>
			<td>Sensoquest</td>
			<td>Labcycler</td>
			<td>Reverse Transcription</td>
		</tr>
		<tr>
			<td>TaqMan Primer</td>
			<td>Thermo Scientific</td>
			<td>-</td>
			<td>qPCR</td>
		</tr>
		<tr>
			<td>iTaq Universal probe supermix</td>
			<td>BioRad GmbH</td>
			<td>1725131</td>
			<td>qPCR</td>
		</tr>
		<tr>
			<td>PCR machine</td>
			<td>Corbett</td>
			<td>Rotor-Gene RG-6000</td>
			<td>qPCR</td>
		</tr>
		<tr>
			<td>TaqMan MicroRNA Reverse Transcription Kit</td>
			<td>Applied Biosystems</td>
			<td>4366596</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>Megaplex RT Primers, Human Pool A v2.1</td>
			<td>Applied Biosystems</td>
			<td>4399966</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>TaqMan PreAmp Master Mix</td>
			<td>Applied Biosystems</td>
			<td>4391128</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>Megaplex PreAmp Primers, Human Pool A v2.1</td>
			<td>Applied Biosystems</td>
			<td>4399933</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>TaqMan Universal Master Mix II, no UNG</td>
			<td>Applied Biosystems</td>
			<td>4440040</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>TaqMan Advanced miRNA Human A Cards</td>
			<td>Applied Biosystems</td>
			<td>A31805</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>Nuclease-free water</td>
			<td>Thermo Scientific</td>
			<td>R0581</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>MgCl2 (25mM)</td>
			<td>Thermo Scientific</td>
			<td>R0971</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>TE, pH 8.0</td>
			<td>Invitrogen</td>
			<td>AM9849</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>7900HT Fast Real-Time PCR System</td>
			<td>Applied Biosystems</td>
			<td>4351405</td>
			<td>TaqMan Array</td>
		</tr>
		<tr>
			<td>TaqMan Array Card Sealer</td>
			<td>Applied Biosystems</td>
			<td>-</td>
			<td>TaqMan Array</td>
		</tr>
	</tbody>
</table>

enrichment of native lipoprotein particles with microrna and subsequent determination of their absolute/relative microrna content and their cellular transfer rate

Lipoprotein particles are predominately transporters of lipids and cholesterol in the bloodstream. Furthermore, they contain small amounts of strands of noncoding microRNA (miRNA). In general, miRNA alters the protein expression profile due to interactions with messenger-RNA (mRNA). Thus, knowledge of the relative and absolute miRNA content of lipoprotein particles is essential to estimate the biological effect of cellular particle uptake. Here, a quantitative real-time polymerase chain reaction (qPCR)-based protocol is presented to determine the absolute miRNA content of lipoprotein particles&#8212;exemplified shown for native and miRNA-enriched lipoprotein particles. The relative miRNA content is quantified using multiwell microfluidic array cards. Furthermore, this protocol allows scientists to estimate the cellular miRNA and, thus, the lipoprotein particle uptake rate. A significant increase of the cellular miRNA level is observable when using high-density lipoprotein (HDL) particles artificially loaded with miRNA, whereas incubation with native HDL particles yields no significant effect due to their rather low miRNA content. In contrast, the cellular uptake of low-density lipoprotein (LDL) particles&#8212;neither with native miRNA nor artificially loaded with it&#8212;did not alter the cellular miRNA level.

Watch this Scientific Journal Video about Enrichment of Native Lipoprotein Particles with microRNA and Subsequent Determination of Their Absolute/Relative microRNA Content and Their Cellular Transfer 

Enrichment of Native Lipoprotein Particles with microRNA and Subsequent Determination of Their Absolute/Relative microRNA Content and Their Cellular Transfer Rate

Here, a quantitative real-time polymerase chain reaction-based protocol is presented for the determination of the native micro-RNA content (absolute/relative) of lipoprotein particles. In addition, a method for increasing the micro-RNA level, as well as a method for determining the cellular uptake rate of lipoprotein particles, is demonstrated.

Lipoprotein particles are predominately transporters of lipids and cholesterol in the bloodstream. Furthermore, they contain small amounts of strands of ...

enrichment-native-lipoprotein-particles-with-microrna-subsequent

Research

JoVE Journal

Biochemistry

8.6K Views.  Medical University Vienna. Here, a quantitative real-time polymerase chain reaction-based protocol is presented for the determination of the native micro-RNA content (absolute/relative) of lipoprotein particles. In addition, a method for increasing the micro-RNA level, as well as a method for determining the cellular uptake rate of lipoprotein particles, is demonstrated.

Video: Enrichment of Native Lipoprotein Particles with microRNA and Subsequent Determination of Their Absolute/Relative microRNA Content and Their Cellular Transfer Rate

An Efficient Method for the Synthesis of Peptoids with Mixed Lysine-type/Arginine-type Monomers and Evaluation of Their Anti-leishmanial Activity

This protocol describes the manual solid-phase synthesis of linear peptoids that contain two differently functionalized cationic monomers. In this procedure amino functionalized 'lysine' and guanido functionalized 'arginine' peptoid monomers can be included within the same peptoid sequence. This procedure uses on-resin (N-(1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) or Dde protection, orthogonal conditions to the Boc protection of lysine monomers. Subsequent deprotection allows an efficient on-resin guanidinylation reaction to form the arginine residues. The procedure is compatible with the commonly used submonomer method of peptoid synthesis, allowing simple peptoids to be made using common laboratory equipment and commercially available reagents. The representative synthesis, purification and characterization of two mixed peptoids is described. The evaluation of these compounds as potential anti-infectives in screening assays against Leishmania mexicana is also described. The protozoan parasite L. mexicana is a causative agent of cutaneous leishmaniasis, a neglected tropical disease that affects up to 12 million people worldwide.

A protocol to synthesize peptoids with mixed cationic functionality in the same sequence is presented (lysine- and arginine-type monomers). Subsequent testing of these compounds against Leishmania mexicana, the protozoan parasites that cause cutaneous leishmaniasis, is also described.

This protocol describes the manual solid-phase synthesis of linear peptoids that contain two differently functionalized cationic monomers. In this ...

Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor diffusion. Oxygen- and moisture-sensitive compounds are prepared and isolated under an inert atmosphere (N2) using either a vacuum gas manifold or a glove box. As an example of azaborine synthesis, we demonstrate the synthesis and purification of the volatile N-H-B-ethyl-1,2-azaborine by a five-step sequence involving distillation and column chromatography for the isolation of products. T4 lysozyme mutants L99A and L99A/M102Q are expressed with Escherichia coli RR1 strain. Standard protocols for chemical cell lysis followed by purification using carboxymethyl ion exchange column affords protein of sufficiently high purity for crystallization. Protein crystallization is performed in various concentrations of precipitant at different pH ranges using the hanging drop vapor diffusion method. Complex preparation with the small molecules is carried out by vapor diffusion method under an inert atmosphere. X-ray diffraction analysis of the crystal complex provides unambiguous structural evidence of binding interactions between the protein binding site and 1,2-azaborines.

A protocol for the synthesis of 1,2-azaborines and the preparation of their protein complexes with T4 lysozyme mutants is presented.

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor ...

Determination of the Glycogen Content in Cyanobacteria

Cyanobacteria accumulate glycogen as a major intracellular carbon and energy storage&#160;during photosynthesis. Recent developments in research have highlighted complex mechanisms of glycogen metabolism, including the diel cycle of biosynthesis and catabolism, redox regulation, and the involvement of non-coding RNA. At the same time, efforts are being made to redirect carbon from glycogen to desirable products in genetically engineered cyanobacteria to enhance product yields. Several methods are used to determine the glycogen contents in cyanobacteria, with variable accuracies and technical complexities. Here, we provide a detailed protocol for the reliable determination of the glycogen content in cyanobacteria that can be performed in a standard life science laboratory. The protocol entails the selective precipitation of glycogen from the cell lysate and the enzymatic depolymerization of glycogen to generate glucose monomers, which are detected by a glucose oxidase-peroxidase (GOD-POD) enzyme coupled assay. The method has been applied to Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002, two model cyanobacterial species that are widely used in metabolic engineering. Moreover, the method successfully showed differences in the glycogen contents between the wildtype and mutants defective in regulatory elements or glycogen biosynthetic genes.

Here, we present a reliable and easy assay to measure the glycogen content in cyanobacterial cells. The procedure entails precipitation, selectable depolymerization, and the detection of glucose residues. This method is suitable for both wildtype and genetically engineered strains and can facilitate the metabolic engineering of cyanobacteria.

Cyanobacteria accumulate glycogen as a major intracellular carbon and energy storage&#160;during photosynthesis. Recent developments in research have ...

Highly Sensitive and Quantitative Detection of Proteins and Their Isoforms by Capillary Isoelectric Focusing Method

Immunoblotting has become a routine technique in many laboratories for protein characterization from biological samples. The following protocol provides an alternative strategy, capillary isoelectric focusing (cIEF), with many advantages compared to conventional immunoblotting. This is an antibody-based, automated, rapid, and quantitative method in which a complete western blotting procedure takes place inside an ultrathin capillary. This technique does not require a gel to transfer to a membrane, stripping of blots, or x-ray films, which are typically required for conventional immunoblotting. Here, proteins are separated according to their charge (isoelectric point; pI), using less than a microliter (400 nL) of total protein lysate. After electrophoresis, proteins are immobilized onto the capillary walls by ultraviolet light treatment, followed by primary and secondary (horseradish peroxidase (HRP) conjugated) antibody incubation, whose binding is detected through enhanced chemiluminescence (ECL), generating a light signal that can be captured and recorded by a charge-coupled device (CCD) camera. The digital image can be analyzed and quantified (peak area) using software. This high throughput procedure can handle 96 samples at a time; is highly sensitive, with protein detection in the picogram range; and produces highly reproducible results because of automation. All of these aspects are extremely valuable when the quantity of samples (e.g., tissue samples and biopsies) is a limiting factor. The technique has wider applications as well, including screening of drugs or antibodies, biomarker discovery, and diagnostic purposes.

Capillary isoelectric focusing is an antibody-based, ultrasensitive, high throughput technique, enabling detailed characterization of proteins and their isoforms from extremely small biological samples. The following describes a protocol for detection and quantification of specific proteins and their isoforms in an automated and robotized manner.

Immunoblotting has become a routine technique in many laboratories for protein characterization from biological samples. The following protocol provides ...

Formation of Covalent DNA Adducts by Enzymatically Activated Carcinogens and Drugs In Vitro and Their Determination by 32P-postlabeling

Covalent DNA adducts formed by chemicals or drugs with carcinogenic potency are judged as one of the most important factors in the initiation phase of carcinogenic processes. This covalent binding, which is considered the cause of tumorigenesis, is now evaluated as a central dogma of chemical carcinogenesis. Here, methods are described employing the reactions catalyzed by cytochrome P450 and additional biotransformation enzymes to investigate the potency of chemicals or drugs for their activation to metabolites forming these DNA adducts. Procedures are presented describing the isolation of cellular fractions possessing biotransformation enzymes (microsomal and cytosolic samples with cytochromes P450 or other biotransformation enzymes, i.e., peroxidases, NADPH:cytochrome P450 oxidoreductase, NAD(P)H:quinone oxidoreductase, or xanthine oxidase). Furthermore, methods are described that can be used for the metabolic activation of analyzed chemicals by these enzymes as well as those for isolation of DNA. Further, the appropriate methods capable of detecting and quantifying chemical/drug-derived DNA adducts, i.e., different modifications of the 32P-postlabeling technique and employment of radioactive-labeled analyzed chemicals, are shown in detail.

Formation of Covalent DNA Adducts by Enzymatically Activated Carcinogens and Drugs In Vitro and Their Determination by 32P-postlabeling

Evaluating the potency of environmental chemicals and drugs, to be enzymatically bioactivated to intermediates generating covalent DNA adducts, is an important field in the development of cancer and its treatment. Methods are described for compound activation to form DNA adducts, as well as techniques for their detection and quantification.

Covalent DNA adducts formed by chemicals or drugs with carcinogenic potency are judged as one of the most important factors in the initiation phase of ...

Split-BioID &#8212; Proteomic Analysis of Context-specific Protein Complexes in Their Native Cellular Environment

To complement existing affinity purification (AP) approaches for the identification of protein-protein interactions (PPI), enzymes have been introduced that allow the proximity-dependent labeling of proteins in living cells. One such enzyme, BirA* (used in the BioID approach), mediates the biotinylation of proteins within a range of approximately 10 nm. Hence, when fused to a protein of interest and expressed in cells, it allows the labeling of proximal proteins in their native environment. As opposed to AP that relies on the purification of assembled protein complexes, BioID detects proteins that have been marked within cells no matter whether they are still interacting with the protein of interest when they are isolated. Since it biotinylates proximal proteins, one can moreover capitalize on the exceptional affinity of streptavidin for biotin to very efficiently isolate them. While BioID performs better than AP for identifying transient or weak interactions, both AP- and BioID-mass spectrometry approaches provide an overview of all possible interactions a given protein may have. However, they do not provide information on the context of each identified PPI. Indeed, most proteins are typically part of several complexes, corresponding to distinct maturation steps or different functional units. To address this common limitation of both methods, we have engineered a protein-fragments complementation assay based on the BirA* enzyme. In this assay, two inactive fragments of BirA* can reassemble into an active enzyme when brought in close proximity by two interacting proteins to which they are fused. The resulting split-BioID assay thus allows the labeling of proteins that assemble around a pair of interacting proteins. Provided these two only interact in a given context, split-BioID then allows the analysis of specific context-dependent functional units in their native cellular environment. Here, we provide a step-by-step protocol to test and apply split-BioID to a pair of interacting proteins.

Split-BioID &amp;#8212; Proteomic Analysis of Context-specific Protein Complexes in Their Native Cellular Environment

We provide a step-by-step protocol for split-BioID, a protein fragments-complementation assay based on the proximity-labeling technique BioID. Activated on the interaction of two given proteins, it allows the proteomics analysis of context-dependent protein complexes in their native cellular environment. The method is simple, cost-effective and only requires standard laboratory equipment.

To complement existing affinity purification (AP) approaches for the identification of protein-protein interactions (PPI), enzymes have been introduced ...

Spectrophotometric Determination of Phycobiliprotein Content in Cyanobacterium Synechocystis

This is a simple protocol for the quantitative determination of phycobiliprotein content in the model cyanobacterium Synechocystis. Phycobiliproteins are the most important components of phycobilisomes, the major light-harvesting antennae in cyanobacteria and several algae taxa. The phycobilisomes of Synechocystis contain two phycobiliproteins: phycocyanin and allophycocyanin. This protocol describes a simple, efficient, and reliable method for the quantitative determination of both phycocyanin and allophycocyanin in this model cyanobacterium. We compared several methods of phycobiliprotein extraction and spectrophotometric quantification. The extraction procedure as described in this protocol was also successfully applied to other cyanobacteria strains such as Cyanothece sp., Synechococcuselongatus, Spirulina sp., Arthrospira sp., and Nostoc sp., as well as to red algae Porphyridium cruentum. However, the extinction coefficients of specific phycobiliproteins from various taxa can differ and it is, therefore, recommended to validate the spectrophotometric quantification method for every single strain individually. The protocol requires little time and can be performed in any standard life science laboratory since it requires only standard equipment.

Spectrophotometric Determination of Phycobiliprotein Content in Cyanobacterium Synechocystis

Here, we present a protocol to quantitatively determine phycobiliprotein content in the cyanobacterium Synechocystis using a spectrophotometric method. The extraction procedure was also successfully applied to other cyanobacteria and algae strains; however, due to variations in pigment absorption spectra, it is necessary to test the spectrophotometric equations for each strain individually.

This is a simple protocol for the quantitative determination of phycobiliprotein content in the model cyanobacterium Synechocystis. Phycobiliproteins are ...

Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays

Chloroplasts are the organelles in green plants responsible for carrying out numerous essential metabolic pathways, most notably photosynthesis. Within the chloroplasts, the thylakoid membrane system houses all the photosynthetic pigments, reaction center complexes, and most of the electron carriers, and is responsible for light-dependent ATP synthesis. Over 90% of chloroplast proteins are encoded in the nucleus, translated in the cytosol, and subsequently imported into the chloroplast. Further protein transport into or across the thylakoid membrane utilizes one of four translocation pathways. Here, we describe a high-yield method for isolation of transport-competent thylakoids from peas (Pisum sativum), along with transport assays through the three energy-dependent cpTat, cpSec1, and cpSRP-mediated pathways. These methods enable experiments relating to thylakoid protein localization, transport energetics, and the mechanisms of protein translocation across biological membranes.

We present protocols herein for high-yield isolation of physiologically active thylakoids and protein transport assays for the chloroplast twin arginine translocation (cpTat), secretory (cpSec1), and signal recognition particle (cpSRP) pathways.

Chloroplasts are the organelles in green plants responsible for carrying out numerous essential metabolic pathways, most notably photosynthesis. Within ...

Isolation of Lipoprotein Particles from Chicken Egg Yolk for the Study of Bacterial Pathogen Fatty Acid Incorporation into Membrane Phospholipids

Staphylococcus aureus and other Gram-positive pathogens incorporate fatty acids from the environment into membrane phospholipids. During infection, the majority of exogenous fatty acids are present within host lipoprotein particles. Uncertainty remains as to the reservoirs of host fatty acids and the mechanisms by which bacteria extract fatty acids from the lipoprotein particles. In this work, we describe protocols for enrichment of low-density lipoprotein (LDL) particles from chicken egg yolk and determining whether LDLs serve as fatty acid reservoirs for S. aureus. This method exploits unbiased lipidomic analysis and chicken LDLs, an effective and economical model for the exploration of interactions between LDLs and bacteria. The analysis of S. aureus integration of exogenous fatty acids from LDLs is performed using high-resolution/accurate mass spectrometry and tandem mass spectrometry, enabling the characterization of the fatty acid composition of the bacterial membrane and unbiased identification of novel combinations of fatty acids that arise in bacterial membrane lipids upon exposure to LDLs. These advanced mass spectrometry techniques offer an unparalleled perspective of fatty acid incorporation by revealing the specific exogenous fatty acids incorporated into the phospholipids. The methods outlined here are adaptable to the study of other bacterial pathogens and alternative sources of complex fatty acids.

This method provides a framework for studying incorporation of exogenous fatty acids from complex host sources into bacterial membranes, particularly Staphylococcus aureus. To achieve this, protocols for the enrichment of lipoprotein particles from chicken egg yolk and subsequent fatty acid profiling of bacterial phospholipids utilizing mass spectrometry are described.

Staphylococcus aureus and other Gram-positive pathogens incorporate fatty acids from the environment into membrane phospholipids. During infection, the ...

Enrichment of Mammalian Tissues and Xenopus Oocytes with Cholesterol

Cholesterol enrichment of mammalian tissues and cells, including Xenopus oocytes used for studying cell function, can be accomplished using a variety of methods. Here, we describe two important approaches used for this purpose. First, we describe how to enrich tissues and cells with cholesterol using cyclodextrin saturated with cholesterol using cerebral arteries (tissues) and hippocampal neurons (cells) as examples. This approach can be used for any type of tissue, cells, or cell lines. An alternative approach for cholesterol enrichment involves the use of low-density lipoprotein (LDL). The advantage of this approach is that it uses part of the natural cholesterol homeostasis machinery of the cell. However, whereas the cyclodextrin approach can be applied to enrich any cell type of interest with cholesterol, the LDL approach is limited to cells that express LDL receptors (e.g., liver cells, bone marrow-derived cells such as blood leukocytes and tissue macrophages), and the level of enrichment depends on the concentration and the mobility of the LDL receptor. Furthermore, LDL particles include other lipids, so cholesterol delivery is nonspecific. Second, we describe how to enrich Xenopus oocytes with cholesterol using a phospholipid-based dispersion (i.e., liposomes) that includes cholesterol. Xenopus oocytes constitute a popular heterologous expression system used for studying cell and protein function. For both the cyclodextrin-based cholesterol enrichment approach of mammalian tissue (cerebral arteries) and for the phospholipid-based cholesterol enrichment approach of Xenopus oocytes, we demonstrate that cholesterol levels reach a maximum following 5 min of incubation. This level of cholesterol remains constant during extended periods of incubation (e.g., 60 min). Together, these data provide the basis for optimized temporal conditions for cholesterol enrichment of tissues, cells, and Xenopus oocytes for functional studies aimed at interrogating the impact of cholesterol enrichment.

Enrichment of Mammalian Tissues and Xenopus Oocytes with Cholesterol

Two methods of cholesterol enrichment are presented: the application of cyclodextrin saturated with cholesterol to enrich mammalian tissues and cells, and the use of cholesterol-enriched phospholipid-based dispersions (liposomes) to enrich Xenopus oocytes. These methods are instrumental for determining the impact of elevated cholesterol levels in molecular, cellular, and organ function.

Cholesterol enrichment of mammalian tissues and cells, including Xenopus oocytes used for studying cell function, can be accomplished using a variety of ...