Manipulating PP2Acα-ASK-JNK signaling to favor apoptotic over necroptotic hepatocyte fate reduces the extent of necrosis and fibrosis upon acute liver injury.

In the widely used Carbon tetrachloride (CCl4)-induced acute liver injury (ALI) mouse model, hepatocytes are known to die from programmed cell death (PCD) processes including apoptosis and necroptosis. Both in vivo and in vitro experiments showed that CCl4 treatment could induce both apoptosis and necroptosis. Treatment of mice with the apoptosis inducer SMAC mimetic reduced necroptosis, led to less pronounced liver damage, and improved overall liver function. By LC-MS/MS, we found that PP2Acα expression was increased in ALI mice liver, and we confirmed its high expression in subacute hepatitis patients. We observed that ALI severity (including aggravated fibrogenesis) was significantly alleviated in hepatocyte-specific PP2Acα conditional knockout (PP2Acα cKO) mice. Furthermore, the relative extent of apoptosis over necroptosis was increased in the PP2Acα cKO ALI mice. Pursuing the idea that biasing the type of PCD towards apoptosis may reduce liver damage, we found that treatment of PP2Acα cKO ALI mice with the apoptosis inhibitor z-Vad-fmk increased the extent of necroptosis and caused severer damage. Mechanistically, disruption of PP2Acα prevents the dephosphorylation of pASK1(Ser967), thereby preventing the sustained activation of JNK. Inhibition of PP2Acα prevents CCl4-induced liver injury and fibrogenesis by disrupting ASK/JNK pathway mediated PCD signaling, ultimately improving liver function by biasing hepatocytes towards an apoptotic rather than necroptotic cell fate. Thus, targeting PP2A and/or ASK1 to favor apoptotic over necroptotic hepatocyte fate may represent an attractive therapeutic strategy for treating ALI.

Paired assessment of liver telomere lengths in hepatocellular cancer is a reliable predictor of disease persistence.

In the present study, we used a small series of highly defined patients, where we had matched timed peripheral blood samples (PBS), as well as paired liver biopsies obtained during collection of blood samples from patients with diagnosed hepatocellular carcinoma (HCC) and compared the correlation between the changes of telomere lengths in these defined samples. Patients included had either HCC alone or in conjunction with either pre-existing hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. PCR-based assay incorporating primers to the telomeric hexamer repeats to polymerize and detect telomeric DNA was used. The average telomere length for each independent assessment was measured by seeing the differences in the intensity of the sample's telomere signal (T) to the signal from a single-copy gene (S-, ß-globin) to estimate the standard ratio. Our results provide the first convincing evidence that PBS may be utilized to assay telomere shortening as a predictor for disease persistence in HCC resulting after HBV or HCV infection, but not in non-infectious cause-stimulated HCC. These findings provide incipient opportunity to develop telomere length assessment as a biomarker tool for prediction of HCC in patients with HBV or HCV infection, as well as to gauge responses to chemotherapy and other treatment modalities.

PP2Acα positively regulates the termination of liver regeneration in mice through the AKT/GSK3ß/Cyclin D1 pathway.

BACKGROUND & AIMS: Liver injury triggers a highly organized and ordered liver regeneration (LR) process. Once regeneration is complete, a stop signal ensures that the regenerated liver is an appropriate functional size. The inhibitors and stop signals that regulate LR are unknown, and only limited information is available about these mechanisms. METHODS: A 70% partial hepatectomy (PH) was performed in hepatocyte-specific PP2Acα-deleted (PP2Acα(-/-)) and control (PP2Acα(+/+)) mice. LR was estimated by liver weight, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and cell proliferation, and the related cellular signals were analyzed. RESULTS: We found that the catalytic subunit of PP2A was markedly upregulated during the late stage of LR. PP2Acα(-/-) mice showed prolonged LR termination, an increased liver size compared to the original mass and lower levels of serum ALT and AST compared with control mice. In these mice, cyclin D1 protein levels, but not mRNA levels, were increased. Mechanistically, AKT activated by the loss of PP2Acα inhibited glycogen synthase kinase 3ß (GSK3ß) activity, which led to the accumulation of cyclin D1 protein and accelerated hepatocyte proliferation at the termination stage. Treatment with the PI3K inhibitor wortmannin at the termination stage was sufficient to inhibit cyclin D1 accumulation and hepatocyte proliferation. CONCLUSIONS: PP2Acα plays an essential role in the proper termination of LR via the AKT/GSK3ß/Cyclin D1 pathway. Our findings enrich the understanding of the molecular mechanism that controls the termination of LR and provides a potential therapeutic target for treating liver injury.