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Mesenchymal stromal cells (MSCs), also known as mesenchymal stem cells, have been intensely investigated for clinical applications within the last decades. However, the majority of registered clinical trials applying MSC therapy for diverse human diseases have fallen short of expectations, despite the encouraging pre-clinical outcomes in varied animal disease models. This can be attributable to inconsistent criteria for MSCs identity across studies and their inherited heterogeneity. Nowadays, with the emergence of advanced biological techniques and substantial improvements in bio-engineered materials, strategies have been developed to overcome clinical challenges in MSC application. Here in this review, we will discuss the major challenges of MSC therapies in clinical application, the factors impacting the diversity of MSCs, the potential approaches that modify MSC products with the highest therapeutic potential, and finally the usage of MSCs for COVID-19 pandemic disease.

Mechanosensitive (MS) ion channels are a ubiquitous type of molecular force sensor sensing forces from the surrounding bilayer. The profound structural diversity in these channels suggests that the molecular mechanisms of force sensing follow unique structural blueprints. Here we determine the structures of plant and mammalian OSCA/TMEM63 proteins, allowing us to identify essential elements for mechanotransduction and propose roles for putative bound lipids in OSCA/TMEM63 mechanosensation. Briefly, the central cavity created by the dimer interface couples each subunit and modulates dimeric OSCA/TMEM63 channel mechanosensitivity through the modulating lipids while the cytosolic side of the pore is gated by a plug lipid that prevents the ion permeation. Our results suggest that the gating mechanism of OSCA/TMEM63 channels may combine structural aspects of the ‘lipid-gated’ mechanism of MscS and TRAAK channels and the calcium-induced gating mechanism of the TMEM16 family, which may provide insights into the structural rearrangements of TMEM16/TMC superfamilies. Mechanosensitive channels exhibit large structural variations. Here, the authors reveal that OSCA channels exhibit different oligomeric states and are gated/regulated by lipids at different locations in response to physical forces.

The transmembrane voltage gradient is a general physico-chemical cue that regulates diverse biological function through voltage-gated ion channels. How voltage sensing mediates ion flows remains unknown at the molecular level. Here, we report six conformations of the human Eag2 (hEag2) ranging from closed, pre-open, open, and pore dilation but non-conducting states captured by cryo-electron microscopy (cryo-EM). These multiple states illuminate dynamics of the selectivity filter and ion permeation pathway with delayed rectifier properties and Cole-Moore effect at the atomic level. Mechanistically, a short S4-S5 linker is coupled with the constrict sites to mediate voltage transducing in a non-domain-swapped configuration, resulting transitions for constrict sites of F464 and Q472 from gating to open state stabilizing for voltage energy transduction. Meanwhile, an additional potassium ion occupied at positions S6 confers the delayed rectifier property and Cole-Moore effects. These results provide insight into voltage transducing and potassium current across membrane, and shed light on the long-sought Cole-Moore effects. Human Eag2 is a voltage-gated potassium channel with unique delayed rectifying gating kinetics. Here, authors show how voltage opens the channel and illuminate a mechanism of delayed rectifier gating.

Understanding how the genome is organized into multi-level chromatin structures within cells and how these chromatin structures regulate gene transcription influencing animal development and human diseases has long been a major goal in genetics and cell biology. Recent evidence suggests that chromatin structure formation and remodeling is regulated not only by chromatin loop extrusion but also by phase-separated condensates. Here, we discuss recent findings on the mechanisms of chromatin organization mediated by phase separation, with a focus on the roles of phase-separated condensates in chromatin structural dysregulation in human diseases. Indeed, these mechanistic revelations herald promising therapeutic strategies targeting phase-separated condensates—leveraging their intrinsic biophysical susceptibilities to restore chromatin structure dysregulated by aberrant phase separation.

Neural stem cells (NSCs) are shielded from viral infection by interferon (IFN) defense. As individuals age, activation of NSC decreases with a significant decline of stemness marker Sex‐determining region Y box 2 (Sox2) while IFN signaling enhances (Kalamakis et al , 2019). Given that low‐level type‐I IFN under normal physiological conditions can promote dormant hematopoietic stem cell differentiation (Baldridge et al , 2010), whether there is an inner connection between IFN signaling and NSC function remains elusive. In this issue of EMBO Molecular Medicine , Carvajal Ibanez et al (2023) reveal that IFN‐β, a type‐I interferon, induces cell‐type‐specific interferon‐stimulated genes (ISGs) and regulates global protein synthesis by orchestrating mTOR1 activity and stem cell cycle that retain NSCs at the G 0 phase and repress Sox2 expression. As a consequence, NSCs exit the activation state and become inclined to differentiation. Graphical Abstract F. Wang and D. Pei discuss the study by Carvajal Ibanez et al (in this issue of EMBO Mol Med ) that investigates the connection between IFN signaling and neural stem cell functions.

OSCA/TMEM63 channels, which have transporter-like architectures, are bona fide mechanosensitive (MS) ion channels that sense high-threshold mechanical forces in eukaryotic cells. The activation mechanism of these transporter-like channels is not fully understood. Here we report cryo-EM structures of a dimeric OSCA/TMEM63 pore mutant OSCA1.1-F516A with a sequentially extracellular dilated pore in a detergent environment. These structures suggest that the extracellular pore sequential dilation resembles a flower blooming and couples to a sequential contraction of each monomer subunit towards the dimer interface and subsequent extrusion of the dimer interface lipids. Interestingly, while OSCA1.1-F516A remains non-conducting in the native lipid environment, it can be directly activated by lyso-phosphatidylcholine (Lyso-PC) with reduced single-channel conductance. Structural analysis of OSCA1.1-F516A in lyso-PC-free and lyso-PC-containing lipid nanodiscs indicates that lyso-PC induces intracellular pore dilation by attracting the M6b to upward movement away from the intracellular side thus extending the intracellular pore. Further functional studies indicate that full activation of MS OSCA/TMEM63 dimeric channels by high-threshold mechanical force also involves the opening of both intercellular and extracellular pores. Our results provide the fundamental activation paradigm of the unique transporter-like MS OSCA/TMEM63 channels, which is likely applicable to functional branches of the TMEM63/TMEM16/TMC superfamilies. How mechanosensitive OSCA/TMEM63 channels are activated remains a mystery. Here, the authors reveal the landscapes of the activation process of OSCA/TMEM63 channels.

PIEZO channels transmit mechanical force signals to cells, allowing them to make critical decisions during development and in pathophysiological conditions. Their fast/slow inactivation modes have been implicated in mechanopathologies but remain poorly understood. Here, we report several near-atomic resolution cryo-EM structures of fast-inactivating wild-type human PIEZO1 (hPIEZO1) and its slow-inactivating channelopathy mutants with or without its auxiliary subunit MDFIC. Our results suggest that hPIEZO1 has a more flattened and extended architecture than curved mouse PIEZO1 (mPIEZO1). The multi-lipidated MDFIC subunits insert laterally into the hPIEZO1 pore module like mPIEZO1, resulting in a more curved and extended state. Interestingly, the high-resolution structures suggest that the pore lipids, which directly seal the central hydrophobic pore, may be involved in the rapid inactivation of hPIEZO1. While the severe hereditary erythrocytosis mutant R2456H significantly slows down the inactivation of hPIEZO1, the hPIEZO1-R2456H-MDFIC complex shows a more curved and contracted structure with an inner helix twist due to the broken link between the pore lipid and R2456H. These results suggest that the pore lipids may be involved in the mechanopathological rapid inactivation mechanism of PIEZO channels.

Channelrhodopsins are popular optogenetic tools in neuroscience, but remain poorly understood mechanistically. Here we report the cryo-EM structures of channelrhodopsin-2 (ChR2) from Chlamydomonas reinhardtii and H. catenoides kalium channelrhodopsin (KCR1). We show that ChR2 recruits an endogenous N-retinylidene-PE-like molecule to a previously unidentified lateral retinal binding pocket, exhibiting a reduced light response in HEK293 cells. In contrast, H. catenoides kalium channelrhodopsin (KCR1) binds an endogenous retinal in its canonical retinal binding pocket under identical condition. However, exogenous ATR reduces the photocurrent magnitude of wild type KCR1 and also inhibits its leaky mutant C110T. Our results uncover diverse retinal chromophores with distinct binding patterns for channelrhodopsins in mammalian cells, which may further inspire next generation optogenetics for complex tasks such as cell fate control. It is known that channelrhodopsins use all-trans retinal as chromophore for light activation. Here, the authors find that different channelrhodopsins utilize various forms of retinal in mammalian cells, which could inspire next-generation optogenetic tools.

We recently derived mouse expanded potential stem cells (EPSCs) from individual blastomeres by inhibiting the critical molecular pathways that predispose their differentiation. EPSCs had enriched molecular signatures of blastomeres and possessed developmental potency for all embryonic and extra-embryonic cell lineages. Here, we report the derivation of porcine EPSCs, which express key pluripotency genes, are genetically stable, permit genome editing, differentiate to derivatives of the three germ layers in chimeras and produce primordial germ cell-like cells in vitro. Under similar conditions, human embryonic stem cells and induced pluripotent stem cells can be converted, or somatic cells directly reprogrammed, to EPSCs that display the molecular and functional attributes reminiscent of porcine EPSCs. Importantly, trophoblast stem-cell-like cells can be generated from both human and porcine EPSCs. Our pathway-inhibition paradigm thus opens an avenue for generating mammalian pluripotent stem cells, and EPSCs present a unique cellular platform for translational research in biotechnology and regenerative medicine. Gao, Nowak-Imialek, Chen et al. generate porcine and human stem cells that possess expanded developmental potency for both embryonic and extra-embryonic cell lineages.

Neurogenesis, a highly orchestrated process, entails the transition from a pluripotent to neural state and involves neural progenitor cells (NPCs) and neuronal/glial subtypes. However, the precise epigenetic mechanisms underlying fate decision remain poorly understood. Here, we delete KDM6s (JMJD3 and/or UTX), the H3K27me3 demethylases, in human embryonic stem cells (hESCs) and show that their deletion does not impede NPC generation from hESCs. However, KDM6-deficient NPCs exhibit poor proliferation and a failure to differentiate into neurons and glia. Mechanistically, both JMJD3 and UTX are found to be enriched in gene loci essential for neural development in hNPCs, and KDM6 impairment leads to H3K27me3 accumulation and blockade of DNA accessibility at these genes. Interestingly, forced expression of neuron-specific chromatin remodelling BAF (nBAF) rescues the neuron/glia defect in KDM6-deficient NPCs despite H3K27me3 accumulation. Our findings uncover the differential requirement of KDM6s in specifying NPCs and neurons/glia and highlight the contribution of individual epigenetic regulators in fate decisions in a human development model. Neurogenesis is an ordered transition from pluriptotent cells to neural precursor cells (NPCs) to neurons. Here the authors show that loss of the lysine demethylases JMJD3 and UTX leads reduced DNA accessibility at neurogenesis loci in human NPCs, and that the chromatin remodeller BAF can rescue differentiation defects.