RESUMO
BACKGROUND: Ischemia-reperfusion injury (IRI) causes significant morbidity in liver transplantation among other medical conditions. IRI following liver transplantation contributes to poor outcomes and early graft loss. Histone/protein deacetylases (HDACs) regulate diverse cellular processes, play a role in mediating tissue responses to IRI, and may represent a novel therapeutic target in preventing IRI in liver transplantation. METHODS: Using a previously described standardized model of murine liver warm IRI, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were assessed at 24 and 48 h after reperfusion to determine the effect of different HDAC inhibitors. RESULTS: Broad HDAC inhibition with trichostatin-A (TSA) was protective against hepatocellular damage (Pâ <â 0.01 for AST and Pâ <â 0.05 for ALT). Although HDAC class I inhibition with MS-275 provided statistically insignificant benefit, tubastatin-A (TubA), an HDAC6 inhibitor with additional activity against HDAC10, provided significant protection against liver IRI (Pâ <â 0.01 for AST and Pâ <â 0.001 for ALT). Surprisingly genetic deletion of HDAC6 or -10 did not replicate the protective effects of HDAC6 inhibition with TubA, whereas treatment with an HDAC6 BUZ-domain inhibitor, LakZnFD, eliminated the protective effect of TubA treatment in liver ischemia (Pâ <â 0.01 for AST and Pâ <â 0.01 for ALT). CONCLUSIONS: Our findings suggest TubA, a class IIb HDAC inhibitor, can mitigate hepatic IRI in a manner distinct from previously described class I HDAC inhibition and requires the HDAC6 BUZ-domain activity. Our data corroborate previous findings that HDAC targets for therapeutic intervention of IRI may be tissue-specific, and identify HDAC6 inhibition as a possible target in the treatment of liver IRI.
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The importance of glucokinase (GK) in the regulation of insulin secretion has been highlighted by the phenotypes of individuals with activating and inactivating mutations in the glucokinase gene (GCK). Here we report 10 individuals with congenital hyperinsulinism (HI) caused by eight unique activating mutations of GCK. Six are novel and located near previously identified activating mutations sites. The first recognized episode of hypoglycemia in these patients occurred between birth and 24 years, and the severity of the phenotype was also variable. Mutant enzymes were expressed and purified for enzyme kinetics in vitro. Mutant enzymes had low glucose half-saturation concentration values and an increased enzyme activity index compared with wild-type GK. We performed functional evaluation of islets from the pancreata of three children with GCK-HI who required pancreatectomy. Basal insulin secretion in perifused GCK-HI islets was normal, and the response to glyburide was preserved. However, the threshold for glucose-stimulated insulin secretion in perifused glucokinase hyperinsulinism (GCK-HI) islets was decreased, and glucagon secretion was greatly suppressed. Our evaluation of novel GCK disease-associated mutations revealed that the detrimental effects of these mutations on glucose homeostasis can be attributed not only to a lowering of the glucose threshold of insulin secretion but also to a decreased counterregulatory glucagon secretory response. ARTICLE HIGHLIGHTS: Our evaluation of six novel and two previously published activating GCK mutations revealed that the detrimental effects of these mutations on glucose homeostasis can be attributed not only to a lowering of the glucose threshold of insulin secretion but also to a decreased counterregulatory glucagon secretory response. These studies provide insights into the pathophysiology of GCK-hyperinsulinism and the dual role of glucokinase in ß-cells and α-cells to regulate glucose homeostasis.
Assuntos
Hiperinsulinismo Congênito , Hiperinsulinismo , Criança , Humanos , Glucoquinase/genética , Glucagon , Hiperinsulinismo Congênito/genética , Hiperinsulinismo/genética , Glucose , Mutação , FenótipoRESUMO
Liver regeneration is a complex process that restores functional tissue after resection or injury, and it is accompanied by transient adenosine triphosphate depletion and metabolic stress in hepatic parenchymal cells. Heat shock protein 70 (Hsp70) functions as a chaperone during periods of cellular stress and induces the expression of several inflammatory cytokines identified as key players during early liver regeneration. We, therefore, hypothesized that Hsp70 is required for the initiation of regeneration. Investigations were carried out in a 70% partial hepatectomy mouse model with mice lacking inducible Hsp70 (Hsp70(-/-)). Liver regeneration was assessed postoperatively with the liver weight/body weight (LW/BW) ratio, and sera and tissues were collected for analysis. In addition, the expression of Hsp-related genes was assessed in a cohort of 23 human living donor liver transplantation donors. In mice, the absence of Hsp70 was associated with a reduced postoperative LW/BW ratio, Ki-67 staining, and tumor necrosis factor α (TNF-α) expression in comparison with wild-type mice. TNF-α expression was also reduced in livers from Hsp70(-/-) mice after induction with lipopolysaccharide (1 mg/kg). Clinically, the transcription of multiple Hsp genes (especially Hsp70 family members) was up-regulated after donor hepatectomy. Together, these results suggest that the early phase of successful liver regeneration requires the presence of Hsp70 to induce TNF-α. Further studies are required to determine whether Hsp70 contributes to liver regeneration as a chaperone by stabilizing specific interactions required for growth signaling or as a paracrine inflammatory signal, as can occur in models of shock.