Hyperpolarization by Optogenetic Activation of NpHR Channels Promotes Osteogenic Differentiation of Human Dental Follicle Stem Cells

Background: Membrane potential represents one of the fundamental physiological characteristics of cells, playing a critical role in cellular function. Studies have shown that membrane hyperpolarization positively regulates the osteogenic differentiation of mesenchymal stem cells. Optogenetic technology based on the Natronomonas pharaonis halorhodopsin (NpHR) light-activated channel can induce membrane hyperpolarization through optical methods. Given the working principle of optogenetic technology, this study aimed to investigate whether optogenetic activation of NpHR channels could induce membrane hyperpolarization in human dental follicle stem cells (hDFCs)—mesenchymal stem cells derived from dental follicle tissue—to regulate their osteogenic differentiation. Methods: hDFCs were isolated and cultured. Engineered hDFCs expressing the NpHR channels were constructed through lentiviral transduction. Patch clamps were performed to observe the effects of optogenetic activation of NpHR channels on membrane potentials of hDFCs. Single-cell Ca2+ imaging were performed to observe the effects of membrane hyperpolarization via modulation of extracellular K+ concentration ([K+]e) on the intracellular Ca2+ levels of hDFCs. Cell viability assay, transwell chamber assay, wound healing assay, osteogenic differentiation induction, alizarin red staining, alkaline phosphatase (ALP) staining, real-time reverse transcriptase polymerase chain reaction (RT-qPCR) and Western blot (WB) were performed to observe the effects of optogenetic activation of NpHR channels on proliferation, migration, and osteogenic differentiation of NpHR-hDFCs. Results: Reversing membrane hyperpolarization via modulation of extracellular K+ concentration ([K+]e) was shown to suppress osteogenic differentiation of hDFCs, whereas promoting membrane hyperpolarization via opening ATP-sensitive K+ channels was shown to enhance osteogenic differentiation of hDFCs. Hyperpolarizing cells by decreasing [K+]e increased intracellular Ca2+ levels of hDFCs. Optogenetic activation of NpHR channels by an optogenetic system induced membrane hyperpolarization and significantly enhanced the proliferation, migration, and osteogenic differentiation abilities of NpHR-hDFCs. Conclusions: Hyperpolarization by optogenetic activation of NpHR channels can promote hDFCs’ proliferation, migration, and osteogenic differentiation abilities.