Parathyroid Hormone Receptor-1 Signaling Aggravates Hepatic Fibrosis through Upregulating cAMP Response Element Binding Protein-Like 2 (human)
Background & Aims  Parathyroid hormone receptor-1 (PTH1R) is a class B G protein-coupled receptor central to skeletal development, bone turnover, and calcium homeostasis. However, the role of PTH1R signaling in liver fibrosis is largely unknown. Here, the role of PTH1R signaling in the activation of hepatic stellate cells (HSCs) and hepatic fibrosis was examined.    Approach & Results  PTH1R was highly expressed in activated HSCs and fibrotic liver by using human liver specimens or carbon tetrachloride (CCl4)-treated or methionine and choline-deficient diet (MCD)-fed C57/BL6 mice. The mRNA level of hepatic PTH1R was positively correlated to a-smooth muscle actin (a-SMA) in patients with liver cirrhosis. Mice with HSCs-specific PTH1R deletion were protected from CCl4, MCD, or western diet plus low-dose CCl4-induced liver fibrosis. Conversely, parathyroid hormone (PTH) aggravated liver fibrosis in CCl4-treated mice. Mouse primary HSCs and LX2 cell lines were used for in vitro experiments. Molecular analyses by luciferase reporter assays and chromatin-immunoprecipitation assays in combination with mRNA sequencing in HSCs revealed that cAMP response element-binding protein-like 2 (Crebl2), a novel regulator in HSCs treated by PTH that interacted with Mothers against decapentaplegic homolog 3 (SMAD3) and increased the transcription of transforming growth factor ß (TGFß) in activating HSCs and collagen deposition. In agreement, HSCs-specific Crebl2 deletion ameliorated PTH-induced liver fibrosis in CCl4-treated mice.     Conclusions  In both mouse and human models, we found that PTH1R was highly expressed in activated HSCs and fibrotic liver. PTH1R signaling regulated collagen production in the HSCs via Crebl2/SMAD3/TGFß regulatory circuits. Blockade of PTH1R signaling in HSCs might help mitigate the development of liver fibrosis. Overall design: Comparative gene expression profiling analysis of RNA-seq data for mice with or without PTH