Biology subjects

Sitikov, A.

Publications and source records attributed to Sitikov, A..

3 recordsLinked to original sources

bioRxiv2024

Critical role of Gα12 and Gα13 proteins in TGF-β-induced myofibroblast differentiation.

Myofibroblast differentiation, characterized by accumulation of cytoskeletal and extracellular matrix proteins by fibroblasts, is a key process in wound healing and pathogenesis of tissue fibrosis. Transforming growth factor-{beta} (TGF-{beta}) is the most powerful known driver of myofibroblast differentiation. TGF-{beta} signals through transmembrane receptor serine/threonine kinases that phosphorylate Smad transcription factors (Smad2/3) leading to activation of transcription of target genes. Heterotrimeric G proteins mediate a distinct signaling from seven-transmembrane G protein coupled receptors, not commonly linked to Smad activation. We asked if G protein signaling plays any role in TGF-{beta}-induced myofibroblast differentiation, using primary cultured human lung fibroblasts. Activation of Gs by cholera toxin blocked TGF-{beta}-induced myofibroblast differentiation without affecting Smad2/3 phosphorylation. Inhibition of Gi by pertussis toxin, or siRNA-mediated combined knockdown of Gq and G11 had no significant effect on TGF-{beta}-induced myofibroblast differentiation. A combined knockdown of G12 and G13 resulted in a drastic inhibition of TGF-{beta}-stimulated expression of myofibroblast marker proteins (collagen-1, fibronectin, smooth-muscle -actin), with siG12 being significantly more potent than siG13. Mechanistically, a combined knockdown of G12 and G13 resulted in a substantially reduced phosphorylation of Smad2 and Smad3 in response to TGF-{beta}, which was accompanied by a significant decrease in the expression of TGF{beta} receptors (TGFBR1, TGFBR2) and of Smad3 under siG12/13 conditions. In conclusion, our study uncovers a novel role of G12/13 proteins in the control of TGF-{beta} signaling and myofibroblast differentiation.

cell biology↗

bioRxiv2023

Anoctamin-1 is induced by TGF-beta and contributes to lung myofibroblast differentiation

Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by progressive scarring of the lungs and resulting in deterioration in lung function. Transforming growth factor-beta (TGF-{beta}) is one of the most established drivers of fibrotic processes. TGF-{beta} promotes transformation of tissue fibroblasts to myofibroblasts, a key finding in the pathogenesis of pulmonary fibrosis. We report here that TGF-{beta} robustly upregulates the expression of the calcium-activated chloride channel Anoctamin-1 (ANO1) in human lung fibroblasts (HLF) at mRNA and protein levels. ANO1 is readily detected in fibrotic areas of IPF lungs in the same area with smooth muscle alpha-actin (SMA)-positive myofibroblasts. TGF-{beta}-induced myofibroblast differentiation (determined by the expression of SMA, collagen-1 and fibronectin) is significantly inhibited by a specific ANO1 inhibitor, T16Ainh-A01, or by siRNA-mediated ANO1 knockdown. T16Ainh-A01 and ANO1 siRNA attenuate pro-fibrotic TGF-{beta} signaling, including activation of RhoA pathway and AKT, without affecting initial Smad2 phosphorylation. Mechanistically, TGF-{beta} treatment of HLF results in a significant increase in intracellular chloride levels, which is prevented by T16Ainh-A01 or by ANO1 knockdown. The downstream mechanism involves the chloride-sensing "with-no-lysine (K)" kinase (WNK1). WNK1 siRNA significantly attenuates TGF-{beta}-induced myofibroblast differentiation and signaling (RhoA pathway and AKT), whereas the WNK1 kinase inhibitor WNK463 is largely ineffective. Together, these data demonstrate that (i) ANO1 is a TGF-{beta}-inducible chloride channel that contributes to increased intracellular chloride concentration in response to TGF-{beta}; and (ii) ANO1 mediates TGF-{beta}-induced myofibroblast differentiation and fibrotic signaling in a manner dependent on WNK1 protein, but independent of WNK1 kinase activity. NEW & NOTEWORTHYThis study describes a novel mechanism of differentiation of human lung fibroblasts (HLF) to myofibroblasts - the key process in the pathogenesis of pulmonary fibrosis. TGF-{beta} drives the expression of calcium-activated chloride channel anoctmin-1 (ANO1) leading to an increase in intracellular levels of chloride. The latter recruits chloride-sensitive With-No-Lysine (K) kinase (WNK1) to activate pro-fibrotic RhoA and AKT signaling pathways, possibly through activation of mammalian target of rapamycin complex-2 (mTORC2), altogether promoting myofibroblast differentiation.

cell biology↗

bioRxiv2023

A Novel HIF-2α/ARNT Signaling Pathway Protects Against Microvascular Dysfunction and heart failure After Myocardial Infarction

Myocardial infarction (MI) significantly compromises the integrity of the cardiac microvascular endothelial barrier, leading to enhanced leakage and inflammation that contribute to the progression of heart failure. While HIF2 is highly expressed in cardiac endothelial cells (ECs) under hypoxic conditions, its role in regulating microvascular endothelial barrier function during MI is not well understood. In this study, we utilized mice with a cardiac-specific deletion of HIF2, generated through an inducible Cre (Cdh5Cre-ERT2) recombinase system. These mice exhibited no apparent phenotype under normal conditions. However, following left anterior descending (LAD) artery ligation-induced MI, they showed increased mortality associated with enhanced cardiac vascular leakage, inflammation, worsened cardiac function, and exacerbated heart remodeling. These outcomes suggest a protective role for endothelial HIF2 in response to cardiac ischemia. Parallel investigations in human cardiac microvascular endothelial cells (CMVECs) revealed that loss of ecHif2 led to diminished endothelial barrier function, characterized by reduced tight-junction protein levels and increased cell death, along with elevated expression of IL6 and other inflammatory markers. These effects were substantially reversed by overexpressing ARNT, a critical dimerization partner for HIF2 during hypoxia. Additionally, ARNT deletion also led to increased CMVEC permeability. Interestingly, ARNT, rather than HIF2 itself, directly binds to the IL6 promoter to suppress IL6 expression. Our findings demonstrate the critical role of endothelial HIF2 in response to MI and identify the HIF2/ARNT axis as a transcriptional repressor, offering novel insights for developing therapeutic strategies against heart failure following MI.

cell biology↗