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Dysregulation of neural stem cells (NSCs) is associated with several neurodevelopmental disorders, including epilepsy and autism spectrum disorder. The mammalian target of rapamycin (mTOR) integrates the intracellular signals to control cell growth, nutrient metabolism, and protein translation. mTOR regulates many functions in the development of the brain, such as proliferation, differentiation, migration, and dendrite formation. In addition, mTOR is important in synaptic formation and plasticity. Abnormalities in mTOR activity is linked with severe deficits in nervous system development, including tumors, autism, and seizures. Dissecting the wide-ranging roles of mTOR activity during critical periods in development will greatly expand our understanding of neurogenesis.

Single-cell proteomics confidently quantifies cellular heterogeneity, however quantification of post-translational modifications, such as those deposited on histone proteins, remains elusive. Here, we develop a robust mass spectrometry-based method for the unbiased analysis of single-cell histone post-translational modifications (sc-hPTM). sc-hPTM identifies both single- and combinatorial histone post-translational modifications (67 peptidoforms in total), which includes nearly all frequently studied histone post-translational modifications with comparable reproducibility to traditional bulk experiments. As a proof of concept, we treat cells with sodium butyrate, a histone deacetylase inhibitor, and demonstrate that our method can i) distinguish between treated and untreated cells, ii) identify sub-populations of cells with heterogeneous response to the treatment, and iii) reveal differential co-regulation of histone post-translational modifications in the context of drug treatment. The sc-hPTM method enables comprehensive investigation of chromatin heterogeneity at single-cell resolution and provides a further understanding of the histone code. Chromatin structure is regulated by chemical modifications of histone proteins, but measuring these at single-cell resolution has been challenging. Here, the authors develop a mass spectrometry-based method to profile histone modifications in individual cells, revealing chromatin heterogeneity and differential co-regulation.

To determine whether rapamycin affects HLA-B27-mediated gut inflammation in experimental spondyloarthritis (SpA). HLA-B27/human β -microglobulin transgenic (B27-Tg) rats with gut inflammation were treated with rapamycin (1.5 mg/kg intraperitoneally, 3 times a week) or vehicle for 5 weeks. Healthy age-matched wild type (WT) rats were treated in parallel. Gut inflammation was evaluated via stool scoring and histological assessment. Transcriptome and microbiome analyses were performed on colon tissue and cecal luminal contents, respectively. Bulk immune cells were isolated from the colonic lamina propria of B27-Tg and WT animals, treated with rapamycin , and pro-inflammatory cytokine expression was measured using qPCR. Rapamycin treatment reduced stool and colon histological scores in B27-Tg rats compared to vehicle-treated B27-Tg controls. Transcriptome analysis revealed that rapamycin reduced expression of key pro-inflammatory cytokines like , , , , and in B27-Tg colon tissue compared to vehicle-treated B27-Tg controls. treatment of bulk immune cells isolated from B27-Tg rat colon with rapamycin reduced expression of , , and compared to vehicle-treated cells. Rapamycin treatment decreased the abundance of cecum microbiota associated with inflammation in B27-Tg rats. Rapamycin also altered the gut microbiome in WT rats, without associated changes in the tissue transcriptome. Our study demonstrates that rapamycin treatment substantially reduces HLA-B27-mediated gut inflammation in experimental SpA. Results from this pre-clinical model suggest further evaluation of rapamycin as a therapeutic strategy in HLA-B27 associated diseases is warranted.

HLA-B27 is a major risk factor for spondyloarthritis (SpA), yet the underlying mechanisms remain unclear. HLA-B27 misfolding-induced IL-23, which is mediated by endoplasmic reticulum (ER) stress has been hypothesized to drive SpA pathogenesis. Expression of HLA-B27 and human β 2 m (hβ 2 m) in rats (HLA-B27-Tg) recapitulates key SpA features including gut inflammation. Here we determined whether deleting the transcription factor CHOP ( Ddit3− /−), which mediates ER-stress induced IL-23, affects gut inflammation in HLA-B27-Tg animals. ER stress-mediated Il23a overexpression was abolished in CHOP-deficient macrophages. Although CHOP-deficiency also reduced Il23a expression in immune cells isolated from the colon of B27+ rats, Il17a levels were not affected, and gut inflammation was not reduced. Rather, transcriptome analysis revealed increased expression of pro-inflammatory genes, including Il1a , Ifng and Tnf in HLA-B27-Tg colon tissue in the absence of CHOP, which was accompanied by higher histological Z-scores. RNAScope localized Il17a mRNA to the lamina propria of the HLA-B27-Tg rats and revealed similar co-localization with Cd3e (CD3) in the presence and absence of CHOP. This demonstrates that CHOP-deficiency does not improve, but rather exacerbates gut inflammation in HLA-B27-Tg rats, indicating that HLA-B27 is not promoting gut disease through ER stress-induced IL-23. Hence, CHOP may protect rats from more severe HLA-B27-induced gut inflammation.