Opposing roles of HDAC6 in liver regeneration and hepatocarcinogenesis

HDAC6 deficiency aggravates ductular reactions through aggresome-mediated hepatocyte apoptosis

Ductular reactions (DRs) contribute significantly to the occurrence and development of liver disease. While histone deacetylase 6 (HDAC6) is known to regulate injury repair in multiple tissues, its exact role in DRs remains unclear. This study examined the role and underlying mechanism of HDAC6 in DRs using an HDAC6 knockout (HDAC6-/y) male mouse model. Wild type and HDAC6-deficient male mice were administered 3,5 diethoxicarbonyl-1,4 dihydrocollidine (DDC) to induce DRs. The impact of HDAC6 inhibition on aggresome formation was assessed in vitro using AML-12 hepatocytes exposed to H2O2 and treated with tubastatin A (TSA), a selective HDAC6 inhibitor. Fluorescence immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to quantify protein and gene expression levels, respectively. Immunohistochemical and qRT-PCR analyses revealed that HDAC6 deficiency exacerbated DRs and fibrosis, accompanied by increased expression of transforming growth factor β (TGF-β) and activation of the Notch signaling pathway. Additionally, genetic knockout or pharmacological inhibition of HDAC6 promoted hepatocyte apoptosis in vivo and in vitro, as evidenced by elevated caspase3, caspase9, and p53 expression. Furthermore, TSA treatment induced the formation of aggresomes in H2O2-exposed AML-12 hepatocytes, which were encased by vimentin filaments. These findings demonstrate that HDAC6 deficiency promotes DRs and liver fibrosis through the formation of intracellular aggregates, ultimately leading to hepatocyte apoptosis.

Histone Deacetylase 6 Inhibitor 5-Phenylcarbamoylpentyl Selenocyanide (SelSA) Suppresses Hepatocellular Carcinoma by Downregulating Phosphorylation of the Extracellular Signal-Regulated Kinase 1/2 Pathway

Histone deacetylase 6 (HDAC6) enzyme plays a crucial role in a variety of cellular processes related to cancer, and inhibition of HDAC6 is emerging as an effective strategy for cancer treatment. Although several hydroxamate-based HDAC6 inhibitors showed promising anticancer activities, the intrinsic defects such as poor selectivity, stability, and pharmacokinetics limited their application. In this study, a potent selenocyanide-bearing HDAC6 inhibitor, 5-phenylcarbamoylpentyl selenocyanide (SelSA), was evaluated for its antihepatocellular carcinoma (HCC) activity and further explored for its antitumor mechanisms. In vitro studies demonstrated that SelSA exhibited excellent antiproliferative activity against three HCC cells HepG2 (2.3 ± 0.29 μM), Huh7 (0.83 ± 0.48 μM), and LM3 (2.6 ± 0.24 μM). Further studies indicated that SelSA could downregulate the expression of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, inhibit the growth, invasion, and migration of Huh7 cells, and promote their apoptosis. Moreover, SelSA significantly suppressed tumor growth in Huh7 xenograft mouse models. Our findings suggest that SelSA could be a potential therapeutic agent for HCC.

Histone deacetylase 6 deficiency protects the liver against ischemia/reperfusion injury by activating PI3K/AKT/mTOR signaling

Liver transplantation (LT) is the only effective method to treat end-stage liver disease. Hepatic ischemia-reperfusion injury (IRI) continues to limit the prognosis of patients receiving LT. Histone deacetylase 6 (HDAC6) is a unique HDAC member involved in inflammation and apoptosis. However, its role and mechanism in hepatic IRI have not yet been reported. We examined HDAC6 levels in liver tissue from LT patients, mice challenged with liver IRI, and hepatocytes subjected to hypoxia/reoxygenation (H/R). In addition, HDAC6 global-knockout (HDAC6-KO) mice, adeno-associated virus-mediated liver-specific HDAC6 overexpressing (HDAC6-LTG) mice, and their corresponding controls were used to construct hepatic IRI models. Hepatic histology, inflammatory responses, and apoptosis were detected to assess liver injury. The molecular mechanisms of HDAC6 in hepatic IRI were explored in vivo and in vitro. Moreover, the HDAC6-selective inhibitor tubastatin A was used to detect the therapeutic effect of HDAC6 on liver IRI. Together, our results showed that HDAC6 expression was significantly upregulated in liver tissue from LT patients, mice subjected to hepatic I/R surgery, and hepatocytes challenged by hypoxia/reoxygenation (H/R) treatment. Compared with control mice, HDAC6 deficiency mitigated liver IRI by inhibiting inflammatory responses and apoptosis, whereas HDAC6-LTG mice displayed the opposite phenotype. Further molecular experiments show that HDAC6 bound to and deacetylated AKT and HDAC6 deficiency improved liver IRI by activating PI3K/AKT/mTOR signaling. In conclusion, HDAC6 is a key mediator of hepatic IRI that functions to promote inflammation and apoptosis via PI3K/AKT/mTOR signaling. Targeting hepatic HDAC6 inhibition may be a promising approach to attenuate liver IRI.

HDAC6 preserves BNIP3 expression and mitochondrial integrity by deacetylating p53 at lysine 320

HDAC6 has been reported as a deacetylase of p53 at multiple lysine residues, associated with the canonical functions of p53, such as apoptosis and tumor suppression. We have previously reported that p53 acetylation at the lysine 320 site accumulates due to the genetic ablation of HDAC6 in mice liver. However, the biological processes affected by K320 acetylation of p53 are yet to be elucidated. In this study, we demonstrate that K320 acetylation of p53 is regulated by HDAC6 deacetylase activity. HDAC6 knockout mouse brains exhibit a significant accumulation of K320 acetylated p53 compared to other tissues. The level of K320 acetylation of p53 inversely correlates with the level of BNIP3, a direct target of p53 and essential for mitophagy. Notably, overexpressing the deacetylation mimic K320R mutant p53 restored BNIP3 expression in HDAC6 knockout MEFs. Furthermore, we observed that neurons are particularly susceptible to the genetic ablation of HDAC6, impacting BNIP3 expression, which inversely correlates with the accumulation of abnormal mitochondria characterized by swollen cristae. Our findings suggest that HDAC6 plays a crucial role in maintaining BNIP3 expression by deacetylating p53 at the K320 site, which is linked to the structural integrity of mitochondria.

Revamping the innate or innate-like immune cell-based therapy for hepatocellular carcinoma: new mechanistic insights and advanced opportunities

A cancerous tumour termed hepatocellular carcinoma (HCC) is characterized by inflammation and subsequently followed by end-stage liver disease and necrosis of the liver. The liver's continuous exposure to microorganisms and toxic molecules affects the immune response because normal tissue requires some immune tolerance to be safeguarded from damage. Several innate immune cells are involved in this process of immune system activation which includes dendritic cells, macrophages, and natural killer cells. The liver is an immunologic organ with vast quantities of innate and innate-like immune cells subjected to several antigens (bacteria, fungal or viral) through the gut-liver axis. Tumour-induced immune system engagement may be encouraged or suppressed through innate immunological systems, which are recognized promoters of liver disease development in pre-HCC conditions such as fibrosis or cirrhosis, ultimately resulting in HCC. Immune-based treatments containing several classes of drugs have transformed the treatment of several types of cancers in recent times. The effectiveness of such immunotherapies relies on intricate interactions between lymphocytes, tumour cells, and neighbouring cells. Even though immunotherapy therapy has already reported to possess potential effect to treat HCC, a clear understanding of the crosstalk between innate and adaptive immune cell pathways still need to be clearly understood for better exploitation of the same. The identification of predictive biomarkers, understanding the progression of the disease, and the invention of more efficient combinational treatments are the major challenges in HCC immunotherapy. The functions and therapeutic significance of innate immune cells, which have been widely implicated in HCC, in addition to the interplay between innate and adaptive immune responses during the pathogenesis, have been explored in the current review.