Hepatic Deficiency of Augmenter of Liver Regeneration Predisposes to Nonalcoholic Steatohepatitis and Fibrosis

Abstract

Background and Aims The augmenter of liver regeneration (ALR) protein is critical for lipid homeostasis and mitochondrial function. We investigated high‐fat/high‐carbohydrate (HF/HC) diet–induced nonalcoholic fatty liver disease (NAFLD) in wild‐type (WT), hepatocyte‐specific ALR‐knockout (ALR‐H‐KO), and ALR‐heterozygous (ALR‐H‐HET) mice. ALR was measured in serum of human nonalcoholic steatohepatitis (NASH) and NASH‐induced cirrhosis (serum and liver). Approach and Results HF/HC feeding decreased ALR expression in all groups of mice. The otherwise normal ALR‐H‐HET mice gained more weight and steatosis than WT mice when challenged metabolically with the HF/HC diet; ALR‐H‐KO mice gained the least weight and had the least steatosis. These findings were consistent with correspondingly increased triglycerides and cholesterol and altered expression of carnitine palmitoyltransferase 1a, sterol regulatory element‐binding protein, acetyl coenzyme A carboxylase, and fatty acid synthase. All HF/HC‐fed mice developed insulin resistance, the magnitude being lower in ALR‐H‐KO mice. HF/HC‐fed ALR‐H‐HET mice were more resistant to glucose challenge than WT or ALR‐H‐KO mice. The frequency of tumor necrosis factor alpha–producing, interleukin 6 (IL6)–producing, and IL17‐producing cells was greater in ALR‐H‐KO than ALR‐H‐HET and lowest in WT mice. HF/HC feeding did not increase their number in ALR‐H‐KO mice, and the increase in ALR‐H‐HET was greater than that in WT mice except for IL17 cells. Cluster of differentiation 25–positive (CD25+) forkhead box P3–positive CD4+ regulatory T‐cell frequency was lower in ALR‐H‐HET than WT mice and further reduced in ALR‐H‐KO mice; HF/HC reduced regulatory T‐cell frequency only in WT mice. HF/HC‐fed ALR‐H‐HET, but not WT, mice developed fibrosis; and ALR‐H‐KO mice progressed to cirrhosis. White adipose tissue of HF/HC‐fed ALR‐deficient mice developed strong inflammation, indicating bidirectional interactions with the liver. Hepatic and serum ALR levels were significantly reduced in patients with NASH‐cirrhosis. Serum ALR was also significantly lower in patients with NASH. Conclusions Hepatic ALR deficiency may be a critical predisposing factor for aggressive NAFLD progression.

Reply

“…In earlier publications, using an overexpression approach ("gain-of-function") of the mainly mitochondrial 23-kDa ALR, a reduction in hepatic fibrosis and ischemia reperfusion injury (IRI) in steatotic livers was shown. (2) Expression of cytosolic 15-kDa ALR reduced severity of liver injury in a methionine-choline-deficient NASH mouse model. (2) Furthermore, it was shown that cytosolic 15-kDa ALR, different from exogenously applied 15-kDa ALR, diminished triacylglycerol levels and lipoapotosis in vitro by attenuating endoplasmatic stress, increasing lipolytic and decreasing lipogenic gene expression.…”

“…(2) Expression of cytosolic 15-kDa ALR reduced severity of liver injury in a methionine-choline-deficient NASH mouse model. (2) Furthermore, it was shown that cytosolic 15-kDa ALR, different from exogenously applied 15-kDa ALR, diminished triacylglycerol levels and lipoapotosis in vitro by attenuating endoplasmatic stress, increasing lipolytic and decreasing lipogenic gene expression. (3) Additionally, treatment with exogenous ALR reduced hepatic IRI in mice by reducing neutrophil infiltration through less hepatocytic chemokine expression.…”

“…carbohydrate mouse models, they demonstrated an involvement of ALR in lipid metabolism, oxidative stress, and inflammatory response leading to fibrosis. However, ALR is expressed in three isoforms (15, 21, 23 kDa), (2) and their specific roles in this "loss-of-function" strategy is not addressed. In earlier publications, using an overexpression approach ("gain-of-function") of the mainly mitochondrial 23-kDa ALR, a reduction in hepatic fibrosis and ischemia reperfusion injury (IRI) in steatotic livers was shown.…”

“…This was addressed earlier, demonstrating reduced hepatic ALR mRNA levels in patients with steatosis and even more with NASH. (2,3) ALR is regulated, among others, by forkhead box A2 (FOXA2; hepatocyte nuclear factor 3β), which translocates from the nucleus to the cytosol upon treatment with free fatty acids, and whose expression correlates with ALR expression in NAFLD patients. (3) Nuclear factor erythroid 2related factor 2 (Nrf2), another ALR-regulating transcription factor, (2) was shown to attenuate liver steatosis and therefore it is likely that FOXA2 and Nrf2 diminished endogenous ALR levels in hepatic steatosis/NASH.…”

“…(2,3) ALR is regulated, among others, by forkhead box A2 (FOXA2; hepatocyte nuclear factor 3β), which translocates from the nucleus to the cytosol upon treatment with free fatty acids, and whose expression correlates with ALR expression in NAFLD patients. (3) Nuclear factor erythroid 2related factor 2 (Nrf2), another ALR-regulating transcription factor, (2) was shown to attenuate liver steatosis and therefore it is likely that FOXA2 and Nrf2 diminished endogenous ALR levels in hepatic steatosis/NASH. However, the conclusion that ALR deficiency may be a major determinant of accelerated progression of NASH to end-stage liver disease, that is, cirrhosis, is not supported by enhanced ALR levels in patients with cirrhosis (2) or by clinical characterization of patients with mutations in the growth factor erv1-like (GFER) gene (encoding for ALR) showing almost no distinctive feature regarding hepatic function (2) and therefore should to be taken with caution.…”