{
  "abstract": "Introduction Mesenchymal stem cell (MSC)–derived small extracellular vesicles (sEVs), including exosomes, exert pro-angiogenic, anti-fibrotic and immunomodulatory effects in experimental models of ischaemic cardiovascular disease. Recently, two classes of non-vesicular extracellular nanoparticles (NVEPs) -exomeres (28–50 nm) and supermeres (22–32 nm) - were identified in cell secretomes; however, their secretion by MSCs and potential relevance to cardiovascular repair remain unexplored. This PhD project aims to characterise NVEP populations secreted by human MSCs and to investigate their molecular association with pathways relevant to cardiovascular biology.Methods Immortalised human adipose-derived MSCs (hMSC-TERT; Sigma) were validated for mesenchymal identity by tri-lineage differentiation into adipogenic, osteogenic and chondrogenic lineages using histochemical staining. Next, MSCs (~70 million cells per batch) were cultured under standard conditions. 48 hours prior to media collection, cells were washed and maintained in serum-free medium. Using modification of a published protocol (Zhang et al., 2023), the conditioned media was processed via concentration and differential ultracentrifugation to isolate sEV, exomere and supermere fractions. These fractions were analysed by liquid chromatography–mass spectrometry (LC–MS; National Phenome Centre, London). Proteomic datasets were interrogated using gene ontology (GO Biological Process) analysis (ShinyGO) and shared and fraction-specific molecular cargo were investigated.Results Preliminary proteomic analysis (n=1/particle type) identified 687 proteins shared across sEVs, exomeres and supermeres. Distinct protein signatures were also observed, with 170 proteins unique to sEVs, 1 unique to exomeres and 78 unique to supermeres ( figure 1). GO analysis highlighted biological processes related to wound response and cell migration in both sEV and supermere fractions. Additionally, the analysis identified cardiovascular-relevant processes in exomeres and supermeres, including blood vessel morphogenesis, vasculature development and circulatory system development. Cardiovascular-related proteins, including PCSK9 and heat-shock proteins were detected across fractions, with PCSK9 showing highest relative abundance in supermeres.Discussion These preliminary findings demonstrate that human MSCs secrete distinct NVEP populations with unique proteomic profiles. In particular, supermeres display molecular features overlapping with sEV-associated wound-healing pathways while also containing a substantial and distinct protein cargo enriched for vascular development processes. Together, these data suggest that MSC-derived supermeres represent a previously unrecognised nanoparticle population with potential relevance to vascular repair in ischaemic disease. Ongoing work will validate these findings across biological replicates and investigate the functional impact of MSC-derived NVEPs in cardiovascular models .Abstract 532 Figure 1A Venn Diagram depicting the distribution of proteins across different fractions",
  "authors": [
    {
      "affiliations": [
        "National Heart and Lung Institute, Imperial College London, London, United Kingdom"
      ],
      "name": "Annika Keshu"
    },
    {
      "affiliations": [
        "National Heart and Lung Institute, Imperial College London, London, United Kingdom"
      ],
      "name": "Xiaoyu Ren"
    },
    {
      "affiliations": [
        "National Heart and Lung Institute, Imperial College London, London, United Kingdom"
      ],
      "name": "Costanza Emanueli"
    }
  ],
  "title": "532 First characterisation of non-vesicular extracellular nanoparticles secreted by human mesenchymal stem cells",
  "uid": "0d95731f-92a3-5642-b644-af906d341d43"
}