Project description:In mammalian cells, endoplasmic reticulum (ER) passively releases Ca2+ under steady state, but channels involved remain elusive. Here, we report that TMEM41B, an ER-resident membrane protein critical for autophagy, lipid metabolism, and viral infection, functions as an ER Ca2+ release channel. Biochemically, purified recombinant TMEM41B forms a concentration-dependent Ca2+ channel in single-channel electrophysiology assays. Cellularly, TMEM41B deficiency causes ER Ca2+ overload, while overexpression of TMEM41B depletes ER Ca2+. Immunologically, ER Ca2+ overload leads to upregulation of IL-2 and IL-7 receptors in naive T cells, which in turn increases basal signaling of JAK-STAT, AKT-mTOR, and MAPK pathways. This dysregulation drives TMEM41B-deficient naive T cells into a metabolically activated yet immunologically naive state. ER Ca2+ overload also downregulates CD5, lowering the activation threshold of TMEM41B-deficient T cells and leading to heightened T cell responses during infections. In summary, we identify TMEM41B as a concentration-dependent ER Ca2+ release channel, revealing an unexpected role of ER Ca2+ in naive T cell quiescence and responsiveness.
Project description:Cellular quiescence is a reversible and tightly regulated stem cell function that is essential for healthy aging. However, the control elements of tissue-specific renewal, quiescence, and aging remain poorly understood. Using melanocyte stem cells (McSCs) to model and test the regulation of tissue-specific quiescence, we find that stem cell quiescence is neither a singular nor static process. McSCs display remarkable heterogeneity, with a fraction expressing the immune checkpoint protein PD-L1. Differential gene expression profiling identifies tissue-specific control of this immune privilege, specifically during melanocyte stem cell dormancy. In vitro quiescence assays confirm that inducing quiescence is sufficient to drive PD-L1 expression in melanoblasts and PD-L1 subsequently regulates aspects of melanoblast cell cycling. In vivo, a portion of McSCs appear to leverage this immune checkpoint as a key aspect of their dynamics during the dormant stage of the hair cycle. With age, this dynamic becomes unbalanced, tipping towards a higher proportion of PD-L1-expressing McSCs and a more deeply quiescent McSC pool. Collectively, these findings demonstrate that immune checkpoint expression is a physiological attribute of McSC quiescence and offer PD-L1-expressing quiescent stem cells as molecular targets for potential reactivation in regenerative and gerontological medicine.
Project description:The normal aging process is a complex phenomenon associated with physiological alterations in the function of cells and organs over time. Although an attractive candidate for mediating transcriptional dysregulation, the contribution of epigenetic dysregulation to these progressive changes in cellular function remains unclear. In this study, we employed the genome-wide HELP assay to define patterns of cytosine methylation throughout the rat genome, and the LUMA assay to measure global levels of DNA methylation in the same samples. We studied both liver and visceral adipose tissue, and demonstrated significant differences in DNA methylation with age at >5% of sites analyzed. Furthermore, we showed that epigenetic dysregulation with age is a highly tissue-dependent phenomenon. The most distinctive loci were located at intergenic sequences and conserved non-coding elements, and not at promoters nor at CG-dinucleotide dense loci. Finally, we demonstrated that changes in methylation occur consistently near genes that are involved in metabolism and metabolic regulation, implicating their potential role in the pathogenesis of age-related diseases. We conclude that different patterns of epigenetic dysregulation occur in each tissue over time and may cause some of the physiological changes associated with normal aging. Direct comparison of DNA methylation in 18 samples belonging to four groups: young liver (n=6), young adipose tissue (n=4), old liver (n=5), old adipose tissue (n=3), isolated from F344*BN rats (young at ~3 months, old at ~18 months). Each microarray consists of a two-color comparison of a methylation-sensitive representation of the genome (HpaII) with an internal methylation-insensitive control/reference (MspI).