Enhanced Intestinal TGF-ß/SMAD-Dependent Signaling in Simian Immunodeficiency Virus Infected Rhesus Macaques.

Transforming growth factor-ß signaling (TGF-ß) maintains a balanced physiological function including cell growth, differentiation, and proliferation and regulation of immune system by modulating either SMAD2/3 and SMAD7 (SMAD-dependent) or SMAD-independent signaling pathways under normal conditions. Increased production of TGF-ß promotes immunosuppression in Human Immunodeficiency Virus (HIV)/Simian Immunodeficiency Virus (SIV) infection. However, the cellular source and downstream events of increased TGF-ß production that attributes to its pathological manifestations remain unknown. Here, we have shown increased production of TGF-ß in a majority of intestinal CD3-CD20-CD68+ cells from acute and chronically SIV infected rhesus macaques, which negatively correlated with the frequency of jejunum CD4+ T cells. No significant changes in intestinal TGF-ß receptor II expression were observed but increased production of the pSMAD2/3 protein and SMAD3 gene expression in jejunum tissues that were accompanied by a downregulation of SMAD7 protein and gene expression. Enhanced TGF-ß production by intestinal CD3-CD20-CD68+ cells and increased TGF-ß/SMAD-dependent signaling might be due to a disruption of a negative feedback loop mediated by SMAD7. This suggests that SIV infection impacts the SMAD-dependent signaling pathway of TGF-ß and provides a potential framework for further study to understand the role of viral factor(s) in modulating TGF-ß production and downregulating SMAD7 expression in SIV. Regulation of mucosal TGF-ß expression by therapeutic TGF-ß blockers may help to create effective antiviral mucosal immune responses.

Identification, Characterization, and Transcriptional Reprogramming of Epithelial Stem Cells and Intestinal Enteroids in Simian Immunodeficiency Virus Infected Rhesus Macaques.

Epithelial cell injury and impaired epithelial regeneration are considered key features in HIV pathogenesis and contribute to HIV-induced generalized immune activation. Understanding the molecular mechanisms underlying the disrupted epithelial regeneration might provide an alternative approach for the treatment of HIV-mediated enteropathy and immune activation. We have observed a significant increased presence of α defensin5+ (HD5) Paneth cells and proliferating Ki67+ epithelial cells as well as decreased expression of E-cadherin expression in epithelial cells during SIV infection. SIV infection did not significantly influence the frequency of LGR5+ stem cells, but the frequency of HD5+ cells was significantly higher compared to uninfected controls in jejunum. Our global transcriptomics analysis of enteroids provided novel information about highly significant changes in several important pathways like metabolic, TCA cycle, and oxidative phosphorylation, where the majority of the differentially expressed genes were downregulated in enteroids grown from chronically SIV-infected macaques compared to the SIV-uninfected controls. Despite the lack of significant reduction in LGR5+ stem cell population, the dysregulation of several intestinal stem cell niche factors including Notch, mTOR, AMPK and Wnt pathways as well as persistence of inflammatory cytokines and chemokines and loss of epithelial barrier function in enteroids further supports that SIV infection impacts on epithelial cell proliferation and intestinal homeostasis.