Significant lethality following liver resection in A20 heterozygous knockout mice uncovers a key role for A20 in liver regeneration

Abstract

Hepatic expression of A20, including in hepatocytes, increases in response to injury, inflammation and resection. This increase likely serves a hepatoprotective purpose. The characteristic unfettered liver inflammation and necrosis in A20 knockout mice established physiologic upregulation of A20 as integral to the anti-inflammatory and anti-apoptotic armamentarium of hepatocytes. However, the implication of physiologic upregulation of A20 in modulating hepatocytes' proliferative responses following liver resection remains controversial. To resolve the impact of A20 on hepatocyte proliferation and the liver's regenerative capacity, we examined whether decreased A20 expression, as in A20 heterozygous knockout mice, affects outcome following two-third partial hepatectomy. A20 heterozygous mice do not demonstrate a striking liver phenotype, indicating that their A20 expression levels are still sufficient to contain inflammation and cell death at baseline. However, usually benign partial hepatectomy provoked a staggering lethality (440%) in these mice, uncovering an unsuspected phenotype. Heightened lethality in A20 heterozygous mice following partial hepatectomy resulted from impaired hepatocyte proliferation due to heightened levels of cyclin-dependent kinase inhibitor, p21, and deficient upregulation of cyclins D1, E and A, in the context of worsened liver steatosis. A20 heterozygous knockout minimally affected baseline liver transcriptome, mostly circadian rhythm genes. Nevertheless, this caused differential expression of 41000 genes post hepatectomy, hindering lipid metabolism, bile acid biosynthesis, insulin signaling and cell cycle, all critical cellular processes for liver regeneration. These results demonstrate that mere reduction of A20 levels causes worse outcome post hepatectomy than full knockout of bona fide liver pro-regenerative players such as IL-6, clearly ascertaining A20's primordial role in enabling liver regeneration. Clinical implications of these data are of utmost importance as they caution safety of extensive hepatectomy for donation or tumor in carriers of A20/TNFAIP3 single nucleotide polymorphisms alleles that decrease A20 expression or function, and prompt the development of A20-based liver proregenerative therapies. Humans and mice restore their liver mass within 2 weeks of surgical, viral or toxic parenchymal loss via compensatory regrowth, referred to as liver regeneration (LR). 1,2 Adequate LR is contingent upon maintaining a minimum healthy residual liver mass without which hepatocyte proliferation is stunned, resulting in hepatic failure. In liver transplantation (mainly living donor liver transplantation), 'small-for-size' syndrome illustrates this outcome. 3 Incremental 78% and 87% hepatectomy in mice reproduces this syndrome, causing 50% and 100% lethality, respectively. 4 Despite considerable knowledge characterizing the molecular basis of LR, better understanding of this process's shortcomings in the face of extensive resection and/or damage is required for uncovering therapie...

A novel glucagon‐like peptide 1/glucagon receptor dual agonist improves steatohepatitis and liver regeneration in mice

“…An early and transient increase of proinflammatory cytokines is necessary for the exit of hepatocytes from G 0 , (40) but sustained proinflammatory signaling impairs liver regeneration. (41) We show that mice fed the MCD diet lack the priming phase of liver regeneration manifested by the absence of elevations in plasma cytokines and activation of the stress kinases (signal transducer and activator of transcription 3 and JNK) in the liver during the early phases after PH. However, M1G49 mice retained cytokine-mediated priming signaling that likely led to the liver regeneration observed 2 weeks after PH, a time in which humans and mice have already restored liver mass.…”

“…Inflammation controls cell fate during liver regeneration, and in this context, it has dual and opposite effects. An early and transient increase of proinflammatory cytokines is necessary for the exit of hepatocytes from G 0 , but sustained proinflammatory signaling impairs liver regeneration . We show that mice fed the MCD diet lack the priming phase of liver regeneration manifested by the absence of elevations in plasma cytokines and activation of the stress kinases (signal transducer and activator of transcription 3 and JNK) in the liver during the early phases after PH.…”

A20 prevents chronic liver inflammation and cancer by protecting hepatocytes from death

“…10, 11 Interestingly, A20 has been identified as a susceptibility locus for multiple immunopathologies, 12 including autoimmune hepatitis. 13 Using A20 heterozygous mice, or mice that transiently overexpress an A20 cDNA, A20 in liver has been shown to be contributing to liver regeneration after partial hepatectomy 14, 15, 16, 17 and acute toxic hepatitis 18 through combined anti-apoptotic, anti-inflammatory and pro-proliferative functions. 19 …”

A20 Haploinsufficiency Aggravates Transplant Arteriosclerosis in Mouse Vascular Allografts

“…Similarly, mRNA levels of NF-κB dependent VCAM-1 and ICAM-1, 2 molecules that enable vascular adhesion and transmigration of mononuclear cells that are a major source of proinflammatory cytokines (14, 20), were significantly higher in HET vs. WT aortic allografts (Fig. 2C, p<0.05, and p<0.01, respectively).…”

“…At baseline, HET mice are phenotypically indistinguishable from their wild type (WT) littermates(13). However, these mice do uncover a distinct phenotype when subjected to certain procedures such as liver resection(14). We hypothesized that partial loss of A20 may negatively impact TA incidence and severity.…”