Abstract
Objective: To analyze platelet (PLT) characteristics and mitochondrial features in patients with multiple myeloma (MM) , and to investigate the impact of PLT mitochondrial respiration on MM cell proliferation, metabolism, and mitochondrial dynamics. Methods: Peripheral blood was collected from healthy volunteers and newly diagnosed MM (NDMM) patients at Sichuan Provincial People's Hospital between January 2020 and December 2023, and PLTs were isolated. PLT activation and mitochondrial reactive oxygen species (ROS) levels were assessed by scanning and transmission electron microscopy and flow cytometry. Serum levels of PLT-related factors were measured by enzyme-linked immunosorbent assay (ELISA) . MM cell lines (RPMI 8226 and U266) were co-cultured with untreated PLTs from healthy volunteers or with PLTs pretreated with rotenone or oligomycin. MM cell proliferation was assessed by the CCK-8 assay. mRNA expression of metabolism- and mitochondrial dynamics-related genes in MM cells was quantified by real-time quantitative PCR (qPCR) . Drp1 and phosphorylated Drp1 were analyzed by Western blot. Results: Compared with healthy volunteers, MM patients showed increased expression of the PLT activation marker CD41/CD61 [ (2.10 ± 1.15) % vs (0.22 ± 0.19) % , P=0.048], decreased CD42b expression [ (52.80 ± 8.73) % vs (74.58 ± 5.11) % , P=0.020], and elevated mitochondrial ROS levels in PLTs (150.50 ± 17.79 vs 62.45 ± 21.34, P=0.001) . Serum factor analysis showed reduced levels of interleukin-34 (IL-34) and platelet factor 4 (PF4) and increased levels of basic fibroblast growth factor (bFGF) , insulin-like growth factor 1 (IGF-1) , IL-6, P-selectin, platelet-derived growth factor (PDGF) , and transforming growth factor β1 (TGF-β1) in MM patients (all P<0.05) , whereas vascular endothelial growth factor (VEGF) levels did not differ significantly (P=0.086) . In vitro co-culture experiments showed that co-culture with PLTs for 48 h promoted MM cell proliferation, whereas PLTs pretreated with rotenone or oligomycin lost this pro-proliferative effect (all P<0.001) . qPCR showed that co-culture increased mRNA expression of the metabolism-related genes citrate synthase (CS) and lactate dehydrogenase A (LDHA) and the mitochondrial dynamics related genes dynamin-1-like protein (DNM1L) and mitochondrial fission 1 (FIS1) in MM cells (all P<0.05) . Pretreatment with the Drp1 inhibitor Mdivi-1 inhibited DNM1L mRNA expression in MM cells (0.75 ± 0.16 vs 1.00 ± 0.09, P=0.002) ; this inhibition was reversed by subsequent co-culture with PLTs (1.02 ± 0.13 vs 0.75 ± 0.16, P=0.007) . Western blot analysis showed that co-culture with PLTs increased p-Drp1 (Ser616) protein levels in U266 cells (P<0.05) . Conclusion: In vitro experiments suggest that PLTs and their mitochondrial respiratory function may be involved in regulating MM cell proliferation, metabolic reprogramming, and mitochondrial dynamics. However, their relevance and applicability in vivo and in clinical practice require further validation in additional preclinical and clinical studies.