Mechanisms Controlling Stem Cell Differentiation

Abstract

Mesenchymal stem cells are multipotent cells that can differentiate into many cell types. However, the molecular mechanism controlling this process remains unclear. We utilized rat dental follicle stem cells (rDFSCs) and human adipose derived stem cells (hASCs) to study the mechanisms controlling osteogenesis and adipogenesis. Elevations in the intracellular Ca²⁺ concentration are a phenomenon commonly observed during stem cell differentiation but cease after the process is complete. The Transient Receptor Potential Melastatin 4 (TRPM4) is an ion channel that controls Ca²⁺ signals in excitable and non-excitable cells. However, there are no studies on TRPM4 in stem cells. In another study, we investigate the mechanism by which arginine vasopressin (AVP), a neuropeptide hormone secreted mostly from the posterior pituitary gland increased Ca²⁺ signals and inhibited adipogenesis in hASCs.

The overall goal of our studies is to investigate the effect of TRPM4 and AVP on stem cell differentiation and Ca²⁺ signaling. First, we identified TRPM4 gene expression and its characteristics such as Ca²⁺-activated, voltage dependent and monovalent conducting properties in rDFSCs. Molecular suppression of TRPM4 transformed the normal agonist-induced first and secondary phases of Ca²⁺ signals into a gradual and sustained increase which enhanced osteogenesis but inhibited adipogenesis in rDFSCs. Next, we examined TRPM4’s impact on Ca²⁺ signals and adipogenesis in hASCs, which is a more suitable stem cell type for adipogenic studies. Suppression of the TRPM4 diminished the histamine-induced Ca²⁺ signals mainly via H1 receptors. The increases in intracellular Ca²⁺ were due to influx via voltage-dependent Ca²⁺ channels of the L-type (Ca_v1.2) and release from the endoplasmic reticulum (ER). Lastly, we determined the role of AVP on adipogenesis in hASCs. These cells were responsive to AVP stimulation by increasing intracellular Ca²⁺ via V1a receptors, Gq-proteins and the PLC-IP3 pathway. Both Ca²⁺ release from the ER and influx from the extracellular space contribute to the Ca²⁺ signals. AVP supplementation to the differentiation media decreased the number of adipocytes during adipogenesis. The effect of AVP on adipocyte formation was reversed by the V1a receptor blocker V2255. In conclusion, TRPM4 and AVP control Ca²⁺ signals which affect stem cell differentiation.