Assessing compartmentalisation of small non-coding RNAs by fractionation of lipoproteins and extracellular vesicles of human plasma

Funding Acknowledgements

Type of funding sources: None.

Background/Introduction

Circulating small non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and YRNAs, have been implicated in intercellular communication and as biomarkers for cardiometabolic diseases. The putative carriers of ncRNAs are lipoproteins, extracellular vesicles (EVs) and RNA-binding proteins. However, the lack of reliable separation methods for EVs and lipoproteins from human blood hampers the assignment of small ncRNA signatures to different carriers.

Purpose

To study which classes of ncRNAs are carried by EVs or lipoproteins in the circulation.

Methods & Results

In order to minimise the co-isolation of lipoproteins and EVs, size-exclusion chromatography (SEC) was established to improve resolution of nanoparticles from plasma. Mass spectrometry and immunoblotting for EV markers (syntenin-1 and CD9) and apolipoproteins (ApoA1 and ApoB for high- and low-density lipoproteins, respectively) were used to characterise the isolated preparations and identify co-isolating species. Quantitative real-time PCR of each carrier-rich fraction after SEC showed that miRNAs were mainly detected in the late-eluting fractions, enriched in ApoA1-containing lipoproteins. Only a small proportion of miRNAs was associated with fractions rich in albumin or in EVs. On the other hand, YRNAs were predominantly found in the albumin-rich and ApoB-containing fractions. To assess whether lipoproteins are key carriers for ncRNAs, HDL and ApoB immuno-depletion methods were employed. Both lipoprotein depletion methods failed to substantially deplete small ncRNAs from plasma.

Conclusion

We studied the distribution of circulating ncRNAs amongst different SEC fractions from human plasma. We have observed a minor role for lipoproteins as carriers of ncRNAs. Further investigation will focus on using SEC fractionation to assess EVs and RNA-binding proteins and their role as ncRNA carriers in plasma.

Precision Medicine Approach for Cardiometabolic Risk Factors in Therapeutic Apheresis

Lipoprotein apheresis (LA) is currently the most powerful intervention possible to reach a maximal reduction of lipids in patients with familial hypercholesterolemia and lipoprotein(a) hyperlipidemia. Although LA is an invasive method, it has few side effects and the best results in preventing further major cardiovascular events. It has been suggested that the highly significant reduction of cardiovascular complications in patients with severe lipid disorders achieved by LA is mediated not only by the potent reduction of lipid levels but also by the removal of other proinflammatory and proatherogenic factors. Here we performed a comprehensive proteomic analysis of patients on LA treatment using intra-individually a set of differently sized apheresis filters with the INUSpheresis system. This study revealed that proteomic analysis correlates well with routine clinical chemistry in these patients. The method is eminently suited to discover new biomarkers and risk factors for cardiovascular disease in these patients. Different filters achieve reduction and removal of proatherogenic proteins in different quantities. This includes not only apolipoproteins, C-reactive protein, fibrinogen, and plasminogen but also proteins like complement factor B (CFAB), protein AMBP, afamin, and the low affinity immunoglobulin gamma Fc region receptor III-A (FcγRIIIa) among others that have been described as atherosclerosis and metabolic vascular diseases promoting factors. We therefore conclude that future trials should be designed to develop an individualized therapy approach for patients on LA based on their metabolic and vascular risk profile. Furthermore, the power of such cascade filter treatment protocols may improve the prevention of cardiometabolic disease and its complications.