Rabbit Anti-Human HDAC4 monoclonal antibody, clone 25I5M20

Liver fibrosis is widely perceived as a host defense mechanism that aids tissue repair following liver injury. Excessive fibrogenesis, however, serves to disrupt normal liver structure and precedes such irrevocable human pathologies as cirrhosis and hepatocellular carcinoma. Activation of hepatic stellate cells (HSCs) is a hallmark event during liver fibrosis. In the present study we investigated the mechanism by which the lysine deacetylase SIRT1 regulates HSC activation. We report here that SIRT1 levels were decreased in the liver in different mouse models and in cultured HSCs undergoing activation. SIRT1 down-regulation paralleled HDAC4 up-regulation. HDAC4 was recruited to the SIRT1 promoter during HSC activation and removed acetylated histones H3 and H4 from the SIRT1 promoter leading to SIRT1 trans-repression. HDAC4 silencing restored SIRT1 expression and attenuated HSC activation in SIRT1-dependent manner. More important, selective deletion of SIRT1 in HSCs exacerbated CCl4-induced liver fibrosis in mice. Mechanistically, SIRT1 deacetylated PPAR gamma to block HSC activation. Together, our data reveal an HDAC4-SIRT1-PPAR gamma axis that contributes to the regulation of HSC activation and liver fibrosis.

Matrix metalloproteinase-13 (MMP-13) plays a predominant role in endochondral bone formation and bone remodeling. Parathyroid hormone (PTH) stimulates the expression of MMP-13 via Runx2, a bone transcription factor in rat osteoblastic cells (UMR106-01), and histone deacetylase 4 (HDAC4) acts as a corepressor of Runx2. Moreover, microRNAs (miRNAs) play an important role in regulating genes posttranscriptionally. Here, we hypothesized that PTH upregulates the miRNAs targeting HDAC4, which could lead to increased Runx2 activity and MMP-13 expression in rat osteoblastic cells. We identified several miRNAs that putatively target rat HDAC4 using bioinformatics tools. miR-873-3p was significantly upregulated by PTH in rat osteoblasts. miR-873-3p overexpression downregulated HDAC4 protein expression, increased Runx2 binding at the MMP-13 promoter, and increased MMP-13 messenger RNA expression in UMR106-01 cells. A luciferase reporter assay identified the direct targeting of miR-873-3p at the 3 '-untranslated region of HDAC4. Thus, miR-873-3p targeted HDAC4 and relieved the corepressor effect of HDAC4 on Runx2 for MMP-13 expression in rat osteoblasts. This study advances our knowledge of posttranscriptional gene regulation occurring in bone and bone-related diseases and clarifies the role of miRNAs as diagnostic biomarkers.