Following the SPARC: tracking Secreted Protein Acidic and Rich in Cysteine associated with LX-2´s extracellular vesicles as a non-destructive modality to evaluate lipid-based antifibrotic treatments
Abstract Uncovering the complex cellular mechanisms underlying hepatic fibrogenesis, a highly dynamic and active process ultimately responsible for liver failure if left untreated, could expedite the development of effective treatments and noninvasive diagnostic modalities for this often silent pathology. The biochemical complexity of extracellular vesicles (EVs) and their role in intercellular communication make them an attractive tool to look for biomarkers that might become a viable alternative to invasive liver biopsies. We developed a solid set of methods to isolate and characterize EVs from differently treated human hepatic stellate cell (HSC) line LX-2 in vitro, and we investigated the biological effect they exert onto naïve LX-2, proving that EVs do play an active role in fibrogenesis. Electrical/asymmetric flow field-flow fractionation (EAF4) revealed EV subpopulations with different physicochemical behaviors. Proteomic data from our samples was mined for EV-associated proteins whose expression correlated with HSC treatment. Consequently, we chose the secreted protein acidic and cysteine rich (SPARC), a matricellular protein previously reported to be upregulated in activated HSCs, as a proof-of-concept protein to explore the feasibility of using fluorescence nanoparticle tracking analysis as a non-destructive tool for the determination of HSCs’ fibrogenic phenotype based on EVs. We could thus use EVs to directly evaluate the efficacy of treatment with S80, a lipid rich (>75 %) in polyenylphosphatidylcholines (PPC). We found that PPC-rich S80 reduces the relative presence of SPARC-positive EVs. For the first time, we could correlate the cellular response to lipid-based antifibrotic treatment to the relative presence of a candidate protein marker associated with the released EVs. In addition to providing novel insights into PPC treatments, our findings pave the way for more precise and less invasive diagnostic analyses of hepatic fibrogenesis.