Study On The Role And Mechanism Of Senescent Immune Cells In Brown Adipose Tissue Aging

Background:Non-shivering thermogenesis mediated by brown adipose tissue(BAT)plays an important role in maintaining energy homeostasis.With increasing age,BAT gradually becomes senescent characterized by decreased thermogenesis capacity and impaired sympathetic innervation,and contributes to metabolic dysfunction.Senescent immune cells have been reported to drive comprehensive aging of body;however,their role in BAT aging remained unclear.Objective:To identify a population of senescent immune cells which are correlated with BAT aging,explore the effect of these senescent immune cells in BAT aging,clarify the specific regulatory mechanism,and further evaluate the effects of immunoregulatory compound on BAT aging and systemic energy metabolism.Methods:We analyzed single cell RNA sequencing database of BAT from young and old rats,and identified a population of senescent immune cells which were correlated with BAT aging.We next evaluated the infiltration levels of these senescent immune cells in BAT of mice at different ages by immunoblots,flow cytometry and immunofluorescence.We then established adoptive transferring of senescent immune cells and bone marrow chimeric mouse models to clarify the origin of these senescent immune cells,and evaluated the effects of senescent immune cells transplantation on BAT thermogenesis and sympathetic innervation by immunoblots,immunofluorescence,q PCR,indirect calorimetry analysis and cold exposure experiments.We further performed RNA sequencing and RNA immunoprecipitation and deep sequencing to screen and identify the target genes of senescent immune cells,and dissected the specific mechanism for regulating thermogenesis and sympathetic innervation by utilizing AAV-mediated overexpression or knockdown of the target gene.We finally validated the effects of immunoregulatory compound treatment on BAT aging and energy metabolism targeting senescent immune cells.Results:We identified that S100A8~+immune cells were bone marrow-derived proinflammatory and senescent immune cells,and infiltrated BAT of rats and mice with age.Adoptive transferred S100A8~+senescent immune cells preferentially infiltrated BAT,secreted abundant S100A8 protein and reduced thermogenesis capacity and sympathetic innervation of BAT in mice.Mechanistically,S100A8 protein interacted with TLR4 on mature brown adipocytes,activated p38 signaling pathway and reduced RBM3 levels.RBM3 mediated the suppression effects of S100A8 on sympathetic innervation and resultant impaired thermogenesis by stabilizing m RNA of axon guidance-related genes.The immunoregulatory compound paquinimod treatment prevented S100A8protein binding to TLR4,reduced BAT infiltration of senescent immune cells,delayed the BAT aging and improved systemic energy metabolism.Conclusion:With increasing age,bone marrow derived S100A8~+senescent immune cells infiltrated brown adipose tissue,forming immune cell-adipocyte-neuron cell crosstalk,manipulating sympathetic innervation and thus driving brown adipose aging.Therapeutics targeting senescent immune cells provide an avenue to combat BAT aging and age-related metabolic disorder.