Stem-cell therapy is showing great potential in regenerative medicine for their inherent ability to self-renew and differentiate. Biochemical and genetic methods and 3D materials/structures have been developed and making great progress in controlling the development and differentiation of stem cells. One of the major remaining concerns is the invasion of those technologies. In this study, we demonstrate an all-optical and noninvasive approach to precisely induce the differentiation of adipose-derived stem cells (ADSCs) and cerebellar granule neuron progenitor (GNP) cells. We show that the single-time fast-flash of photostimulation by a tightly-focused femtosecond laser, without any optogenetics, can activate endogenous signaling pathways for stem-cell differentiation directly by multiphoton excitation. The significant upregulation of differentiation regulator RUNX2 and Osterix in ADSCs 7 days after photostimulation indicates the osteogenic differentiation of ADSCs. The differentiation was finally confirmed by Alizarin red staining 28 days after photostimulation. The differentiation of GNP cells in vitro and in vivo can also be induced by this method. This noninvasive optical technology hence provides an encouraging advance to activation of signaling pathways in cells and alternative to classic biochemical methods for stem-cell differentiation. This result also provides an optical choice with promising potential for clinical regenerative applications.
Store-operated calcium (SOC) channels, regulated by intracellular Ca<sup>2+</sup> store, are the essential pathway of calcium signaling and participate in a wide variety of cellular activities such as gene expression, secretion and immune response<sup>1</sup>. However, our understanding and regulation of SOC channels are mainly based on pharmacological methods. Considering the unique advantages of optical control, optogenetic control of SOC channels has been developed<sup>2</sup>. However, the process of genetic engineering to express exogenous light-sensitive protein is complicated, which arouses concerns about ethic difficulties in some research of animal and applications in human. In this report, we demonstrate rapid, robust and reproducible two-photon activation of endogenous SOC channels by femtosecond laser without optogenetics. We present that the short-duration two-photon scanning on subcellular microregion induces slow Ca<sup>2+</sup> influx from extracellular medium, which can be eliminated by removing extracellular Ca2+. Block of SOC channels using various pharmacological inhibitors or knockdown of SOC channels by RNA interference reduce the probability of two-photon activated Ca<sup>2+</sup> influx. On the contrary, overexpression of SOC channels can increase the probability of Ca<sup>2+</sup> influx by two-photon scanning. These results collectively indicate Ca<sup>2+</sup> influx through two-photon activated SOC channels. Different from classical pathway of SOC entry activated by Ca<sup>2+</sup> store depletion, STIM1, the sensor protein of Ca<sup>2+</sup> level in endoplasmic reticulum, does not show any aggregation or migration in this two-photon activated Ca<sup>2+</sup> influx, which rules out the possibility of intracellular Ca<sup>2+ </sup>store depletion. Thereby, we propose this all-optical method of two-photon activation of SOC channels is of great potential to be widely applied in the research of cell calcium signaling and related biological research.