Human platelet lysate enhances small lipid droplet accumulation of human MSCs through MAPK phosphorylation.

Abstract

Background: Human platelet lysate (hPL) has emerged as a promising serum substitute to enhance the self-renewal and multipotency of human mesenchymal stem cells (MSCs). Despite its potential, the specific biological mechanisms by which hPL influences MSC phenotypes remain inadequately understood.

Methods: We investigated the biological signaling activated by hPL in two common types of human MSCs: bone marrow-derived MSCs (BMSCs) and adipose-derived MSCs (ASCs). Cell adhesion and cell-matrix interaction were assessed through immunofluorescence staining and western blotting. The impact of hPL on lipid droplet formation in MSCs was thoroughly examined using oil red O/BODIPY staining, semi-quantitative analysis, and qRT-PCR. RNA sequencing and intracellular inhibition assays were also performed to elucidate the mechanisms by which hPL modulates MSC behavior.

Results: MSCs cultured in hPL medium demonstrated a reduction in cell size, spreading area, and vinculin puncta,  while enhancing cell proliferation and lipid droplet accumulation compared to those cultured in control media. Notably, the lipid droplets in hPL-treated MSCs were significantly smaller than those in adipocyte-like cells differentiated from MSCs, highlighting hPL's distinctive role in lipid production. Gene and protein expression profiles of hPL-treated MSCs differed from those in adipocyte-like cells. An angiogenic factor array revealed that hPL-MSCs had a distinct angiogenic factor profile compared to FBS-MSCs, with VEGF expression closely linked to HIF-1α expression. RNA-seq data identified approximately 1,900 differentially expressed genes (DEGs) between hPL-MSCs and FBS-MSCs, with enrichment in focal adhesion, ECM-receptor interaction, and PI3K-Akt/MAPK signaling pathways. Inhibition of MAPK phosphorylation significantly hampered lipid formation in hPL-MSCs, underscoring the pivotal role of MAPK signaling in hPL-driven adipogenesis.

Conclusion: This study reveals the biological mechanisms by which hPL infleunces MSC behavior and differentiation, offering new insights into its potential application in regenerative medicine and tissue engineering.