T-Type Ca2+ Channel Blockers Increase Smooth Muscle Progenitor Cells and Endothelial Progenitor Cells in Bone Marrow Stromal Cells in Culture by Suppression of Cell Death

Crucial role of pro-inflammatory cytokines from respiratory tract upon PM2.5 exposure in causing the BMSCs differentiation in cells and animals

Fine particulate matter exposure may cause health risk, including cardiovascular diseases and cancer. Bone marrow mesenchymal stem cell (BMSC), a typical model for evaluating pollutant toxicity, has been closely linked to these diseases, due to its characteristics of differentiation. We therefore studied the BMSCs differentiation and its roles in inflammatory activation in the respiratory tract upon PM2.5 exposure using both in vitro and in vivo models. BMSCs differentiation into endothelial-like cells (ELCs) and cancer-associated fibroblasts cells (CAFs) was enhanced in response to conditioned medium from PM2.5-treated 16HBE cells. PM2.5 elevated inflammatory cytokines' expression and secretion in 16HBE cells. However, induction of differentiation markers was reduced when IL-1β, IL-6 and COX-2 neutralizing antibodies were added to the conditioned medium. Furthermore, PM2.5 induced ROS formation and NADPH oxidase (NOX) expression in 16HBE cells. DPI (inhibitor of ROS from NOX) or NAC (inhibitor of ROS) supplement reduced PM2.5-induced inflammatory activation and BMSCs differentiation. Likewise, a concomitant disorder of mitochondrial morphology and respiratory chain was observed. In addition, Rot or AA (inhibitor of mitochondrial complex I or III) supplement restored PM2.5-induced toxic effects. Moreover, the results coincided with the in vitro data obtained from SD rats post-exposed to different doses of PM2.5 for 30 days. PM2.5 enhanced the BMSCs differentiation and inflammatory cytokines' expression in respiratory organs of SD rats, including lung and trachea tissue. This study uncovers that PM2.5 promotes the BMSCs differentiation via inflammatory activation mediated by ROS induction from NOX and mitochondria in the respiratory tract.

High extracellular Ca2+ enhances the adipocyte accumulation of bone marrow stromal cells through a decrease in cAMP

Bone marrow stromal cells (BMSCs) are common progenitors of both adipocytes and osteoblasts. We recently suggested that increased [Ca²⁺]_o caused by bone resorption might accelerate adipocyte accumulation in response to treatment with both insulin and dexamethasone. In this study, we investigated the mechanism by which high [Ca²⁺]_o enhances adipocyte accumulation. We used primary mouse BMSCs and evaluated the levels of adipocyte accumulation by measuring Oil Red O staining. CaSR agonists (both Ca²⁺ and Sr²⁺) enhanced the accumulation of adipocytes among BMSCs in response to treatment with both insulin and dexamethasone. We showed that high [Ca²⁺]_o decreases the concentration of cAMP using ELISA. Real-time RT-PCR revealed that increasing the intracellular concentration of cAMP (both chemical inducer (1μM forskolin and 200nM IBMX) and a cAMP analog (10μM pCPT-cAMP)) suppressed the expression of PPARγ and C/EBPα. In addition, forskolin, IBMX, and pCPT-cAMP inhibited the enhancement in adipocyte accumulation under high [Ca²⁺]_o in BMSCs. However, this inhibited effect was not observed in BMSCs that were cultured in a basal concentration of [Ca²⁺]_o. We next observed that the accumulation of adipocytes in the of bone marrow of middle-aged mice (25-40 weeks old) is higher than that of young mice (6 weeks old) based on micro CT. ELISA results revealed that the concentration of cAMP in the bone marrow mononuclear cells of middle-aged mice is lower than that of young mice. These data suggest that increased [Ca²⁺]_o caused by bone resorption might accelerate adipocyte accumulation through CaSR following a decrease in cAMP.

Increased extracellular and intracellular Ca²⁺ lead to adipocyte accumulation in bone marrow stromal cells by different mechanisms

Mesenchymal stem cells found in bone marrow stromal cells (BMSCs) are the common progenitors for both adipocyte and osteoblast. An increase in marrow adipogenesis is associated with age-related osteopenia and anemia. Both extracellular and intracellular Ca(2+) ([Ca(2+)]o and [Ca(2+)]i) are versatile signaling molecules that are involved in the regulation of cell functions, including proliferation and differentiation. We have recently reported that upon treatment of BMSCs with insulin and dexamethasone, both high [Ca(2+)]o and high [Ca(2+)]i enhanced adipocyte accumulation, which suggested that increases in [Ca(2+)]o caused by bone resorption may accelerate adipocyte accumulation in aging and diabetic patients. In this study, we used primary mouse BMSCs to investigate the mechanisms by which high [Ca(2+)]o and high [Ca(2+)]i may enhance adipocyte accumulation. In the process of adipocyte accumulation, two important keys are adipocyte differentiation and the proliferation of BMSCs, which have the potential to differentiate into adipocytes. Use of MTT assay and real-time RT-PCR revealed that high [Ca(2+)]i (ionomycin)-dependent adipocyte accumulation is caused by enhanced proliferation of BMSCs but not enhanced differentiation into adipocytes. Using fura-2 fluorescence-based approaches, we showed that high [Ca(2+)]o (addition of CaCl2) leads to increases in [Ca(2+)]i. Flow cytometric methods revealed that high [Ca(2+)]o suppressed the phosphorylation of ERK independently of intracellular Ca(2+). The inhibition of ERK by U0126 and PD0325901 enhanced the differentiation of BMSCs into adipocytes. These data suggest that increased extracellular Ca(2+) provides the differentiation of BMSCs into adipocytes by the suppression of ERK activity independently of increased intracellular Ca(2+), which results in BMSC proliferation.