HSP90 activity is required for MLKL oligomerisation and membrane translocation and the induction of necroptotic cell death.

Necroptosis is a caspase-independent form of regulated cell death that has been implicated in the development of a range of inflammatory, autoimmune and neurodegenerative diseases. The pseudokinase, Mixed Lineage Kinase Domain-Like (MLKL), is the most terminal known obligatory effector in the necroptosis pathway, and is activated following phosphorylation by Receptor Interacting Protein Kinase-3 (RIPK3). Activated MLKL translocates to membranes, leading to membrane destabilisation and subsequent cell death. However, the molecular interactions governing the processes downstream of RIPK3 activation remain poorly defined. Using a phenotypic screen, we identified seven heat-shock protein 90 (HSP90) inhibitors that inhibited necroptosis in both wild-type fibroblasts and fibroblasts expressing an activated mutant of MLKL. We observed a modest reduction in MLKL protein levels in human and murine cells following HSP90 inhibition, which was only apparent after 15 h of treatment. The delayed reduction in MLKL protein abundance was unlikely to completely account for defective necroptosis, and, consistent with this, we also found inhibition of HSP90 blocked membrane translocation of activated MLKL. Together, these findings implicate HSP90 as a modulator of necroptosis at the level of MLKL, a function that complements HSP90's previously demonstrated modulation of the upstream necroptosis effector kinases, RIPK1 and RIPK3.

Engineering a multimodal nerve conduit for repair of injured peripheral nerve.

Injury to nerve tissue in the peripheral nervous system (PNS) results in long-term impairment of limb function, dysaesthesia and pain, often with associated psychological effects. Whilst minor injuries can be left to regenerate without intervention and short gaps up to 2 cm can be sutured, larger or more severe injuries commonly require autogenous nerve grafts harvested from elsewhere in the body (usually sensory nerves). Functional recovery is often suboptimal and associated with loss of sensation from the tissue innervated by the harvested nerve. The challenges that persist with nerve repair have resulted in development of nerve guides or conduits from non-neural biological tissues and various polymers to improve the prognosis for the repair of damaged nerves in the PNS. This study describes the design and fabrication of a multimodal controlled pore size nerve regeneration conduit using polylactic acid (PLA) and (PLA):poly(lactic-co-glycolic) acid (PLGA) fibers within a neurotrophin-enriched alginate hydrogel. The nerve repair conduit design consists of two types of PLGA fibers selected specifically for promotion of axonal outgrowth and Schwann cell growth (75:25 for axons; 85:15 for Schwann cells). These aligned fibers are contained within the lumen of a knitted PLA sheath coated with electrospun PLA nanofibers to control pore size. The PLGA guidance fibers within the nerve repair conduit lumen are supported within an alginate hydrogel impregnated with neurotrophic factors (NT-3 or BDNF with LIF, SMDF and MGF-1) to provide neuroprotection, stimulation of axonal growth and Schwann cell migration. The conduit was used to promote repair of transected sciatic nerve in rats over a period of 4 weeks. Over this period, it was observed that over-grooming and self-mutilation (autotomy) of the limb implanted with the conduit was significantly reduced in rats implanted with the full-configuration conduit compared to rats implanted with conduits containing only an alginate hydrogel. This indicates return of some feeling to the limb via the fully-configured conduit. Immunohistochemical analysis of the implanted conduits removed from the rats after the four-week implantation period confirmed the presence of myelinated axons within the conduit and distal to the site of implantation, further supporting that the conduit promoted nerve repair over this period of time. This study describes the design considerations and fabrication of a novel multicomponent, multimodal bio-engineered synthetic conduit for peripheral nerve repair.

Upregulation of lymphotoxin beta expression in liver progenitor (oval) cells in chronic hepatitis C.

BACKGROUND: Bipotent liver progenitor (oval) cells with the ability to differentiate into hepatocytes and biliary epithelium have recently been identified in human subjects with hepatitis C. Animal studies suggest that members of the tumour necrosis factor family, including lymphotoxin beta (LT-beta), regulate oval cell proliferation in liver disease, but its role in human liver disease is unclear. AIMS: This study seeks to establish a role for LT-beta in hepatitis C related liver injury and to provide evidence that its increased expression is related to the presence of oval cells. METHODS: Liver biopsy specimens were obtained from patients with chronic hepatitis C virus (HCV) infection (n=20). Control liver samples (n=5) were obtained from liver resection or transplant surgery. LT-beta expression in liver biopsy specimens was studied using quantitative real time polymerase chain reaction and immunohistochemistry. RESULTS: LT-beta mRNA levels were similar in control and HCV liver in the absence of fibrosis. In subjects with portal fibrosis, LT-beta mRNA levels were elevated 2.2-fold over control liver levels (p=0.04). In subjects with bridging fibrosis, LT-beta mRNA levels increased 4.4-fold over control liver levels (p=0.02). LT-beta mRNA levels in subjects with established cirrhosis were increased 3.3-fold compared with controls and 2.6-fold compared with mild liver damage (p=0.02). Immunohistochemical analysis established that LT-beta was expressed by oval cells, inflammatory cells, and small portal hepatocytes. CONCLUSIONS: In chronic HCV infection, LT-beta expression is observed in multiple hepatic cell types, including oval cells. LT-beta expression is significantly increased when fibrosis or cirrhosis is present, suggesting a role for LT-beta in the pathogenesis of chronic hepatitis C and a possible role in oval cell mediated liver regeneration.

Oval cell numbers in human chronic liver diseases are directly related to disease severity.

The risk of developing hepatocellular carcinoma is significantly increased in patients with genetic hemochromatosis, alcoholic liver disease, or chronic hepatitis C infection. The precise mechanisms underlying the development of hepatocellular carcinoma in these conditions are not well understood. Stem cells within the liver, termed oval cells, are involved in the pathogenesis of hepatocellular carcinoma in animal models and may be important in the development of hepatocellular carcinoma in human chronic liver diseases. The aims of this study were to determine whether oval cells could be detected in the liver of patients with genetic hemochromatosis, alcoholic liver disease, or chronic hepatitis C, and whether there is a relationship between the severity of the liver disease and the number of oval cells. Oval cells were detected using histology and immunohistochemistry in liver biopsies from patients with genetic hemochromatosis, alcoholic liver disease, or chronic hepatitis C. Oval cells were not observed in normal liver controls. Oval cell numbers increased significantly with the progression of disease severity from mild to severe in each of the diseases studied. We conclude that oval cells are frequently found in subjects with genetic hemochromatosis, alcoholic liver disease, or chronic hepatitis C. There is an association between severity of liver disease and increase in the number of oval cells consistent with the hypothesis that oval cell proliferation is associated with increased risk for development of hepatocellular carcinoma in chronic liver disease.