Commentary: FGF21 holds promises for treating obesity-related insulin resistance and hepatosteatosis

β-Klotho gene variation is associated with liver damage in children with NAFLD

BACKGROUND & AIM

Non-alcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease in adults and children. Along with obesity, diabetes and insulin resistance, genetic factors strongly impact on NAFLD development and progression. Dysregulated bile acid metabolism and the fibroblast growth factor 19 (FGF19) pathway play a pivotal role in NAFLD pathogenesis. However, the mechanism through which the FGF19 receptor system is associated with liver damage in NAFLD remains to be defined.

METHODS

We evaluated the impact of the rs17618244 G>A β-Klotho (KLB) variant on liver damage in 249 pediatric patients with biopsy-proven NAFLD and the association of this variant with the expression of hepatic and soluble KLB. In vitro models were established to investigate the role of the KLB mutant.

RESULTS

The KLB rs17618244 variant was associated with an increased risk of ballooning and lobular inflammation. KLB plasma levels were lower in carriers of the rs17618244 minor A allele and were associated with lobular inflammation, ballooning and fibrosis. In HepG2 and Huh7 hepatoma cell lines, exposure to free fatty acids caused a severe reduction of intracellular and secreted KLB. Finally, KLB downregulation obtained by the expression of a KLB mutant in HepG2 and Huh7 cells induced intracellular lipid accumulation and upregulation of p62, ACOX1, ACSL1, IL-1β and TNF-α gene expression.

CONCLUSION

In conclusion, we showed an association between the rs17618244 KLB variant, which leads to reduced KLB expression, and the severity of NAFLD in pediatric patients. We can speculate that the KLB protein may exert a protective role against lipotoxicity and inflammation in hepatocytes.

LAY SUMMARY

Genetic and environmental factors strongly impact on the pathogenesis and progression of non-alcoholic fatty liver disease (NAFLD). The FGF19/FGFR4/KLB pathway plays a pivotal role in the pathogenesis of NAFLD. The aim of the study was to investigate the impact of a genetic variant in the KLB gene on the severity of liver disease. Our data suggest that the KLB protein plays a protective role against lipotoxicity and inflammation in hepatocytes.

Fibroblast growth factor 21, fibroblast growth factor receptor 1, and β-Klotho expression in bovine growth hormone transgenic and growth hormone receptor knockout mice

OBJECTIVE

Although growth hormone (GH) and fibroblast growth factor 21 (FGF21) have a reported relationship, FGF21 and its receptor, fibroblast growth factor receptor 1 (FGFR1) and cofactor β-Klotho (KLB), have not been analyzed in chronic states of altered GH action. The objective of this study was to quantify circulating FGF21 and tissue specific expression of Fgf21, Fgfr1, and Klb in mice with modified GH action. Based on previous studies, we hypothesized that bovine GH transgenic (bGH) mice will be FGF21 resistant and GH receptor knockout (GHR-/-) mice will have normal FGF21 action.

DESIGN

Seven-month-old male bGH mice (n=9) and wild type (WT) controls (n=10), and GHR-/- mice (n=8) and WT controls (n=8) were used for all measurements. Body composition was determined before dissection, and tissue weights were measured at the time of dissection. Serum FGF21 levels were evaluated by ELISA. Expression of Fgf21, Fgfr1, and Klb mRNA in white adipose tissue (AT), brown AT, and liver were evaluated by reverse transcription quantitative PCR.

RESULTS

As expected, bGH mice had increased body weight (p=3.70E^-8) but decreased percent fat mass (p=4.87E^-4). Likewise, GHR-/- mice had decreased body weight (p=1.78E^-10) but increased percent fat mass (p=1.52E^-9), due to increased size of the subcutaneous AT depot when normalized to body weight (p=1.60E^-10). Serum FGF21 levels were significantly elevated in bGH mice (p=0.041) and unchanged in GHR-/- mice (p=0.88). Expression of Fgf21, Fgfr1, and Klb mRNA in white AT and liver were downregulated or unchanged in both bGH and GHR-/- mice. The only exception was Fgf21 expression in brown AT of GHR-/-, which trended toward increased expression (p=0.075).

CONCLUSIONS

In accordance with our hypothesis, we provide evidence that circulating FGF21 is increased in bGH animals, but remains unchanged in GHR-/- mice. Downregulation or no change in Fgf21, Fgfr1, and Klb expression are seen in white AT, brown AT, and liver of bGH and GHR-/- mice when compared to their respective controls, except for an increase in brown AT Fgf21 expression in GHR-/- mice, which could suggest a possible link to increased thermogenic potential in these mice. Overall, these results suggest possible modulation of FGF21 by GH resulting in FGF21 resistance or changes in FGF21 levels due to GH induced changes in liver size or kidney function.

Additive protection by LDR and FGF21 treatment against diabetic nephropathy in type 2 diabetes model

The onset of diabetic nephropathy (DN) is associated with both systemic and renal changes. Fibroblast growth factor (FGF)-21 prevents diabetic complications mainly by improving systemic metabolism. In addition, low-dose radiation (LDR) protects mice from DN directly by preventing renal oxidative stress and inflammation. In the present study, we tried to define whether the combination of FGF21 and LDR could further prevent DN by blocking its systemic and renal pathogeneses. To this end, type 2 diabetes was induced by feeding a high-fat diet for 12 wk followed by a single dose injection of streptozotocin. Diabetic mice were exposed to 50 mGy LDR every other day for 4 wk with and without 1.5 mg/kg FGF21 daily for 8 wk. The changes in systemic parameters, including blood glucose levels, lipid profiles, and insulin resistance, as well as renal pathology, were examined. Diabetic mice exhibited renal dysfunction and pathological abnormalities, all of which were prevented significantly by LDR and/or FGF21; the best effects were observed in the group that received the combination treatment. Our studies revealed that the additive renal protection conferred by the combined treatment against diabetes-induced renal fibrosis, inflammation, and oxidative damage was associated with the systemic improvement of hyperglycemia, hyperlipidemia, and insulin resistance. These results suggest that the combination treatment with LDR and FGF21 prevented DN more efficiently than did either treatment alone. The mechanism behind these protective effects could be attributed to the suppression of both systemic and renal pathways.

Role of histone deacetylase 9 in regulating adipogenic differentiation and high fat diet-induced metabolic disease

Adipose tissue serves as both a storage site for excess calories and as an endocrine organ, secreting hormones such as adiponectin that promote metabolic homeostasis. In obesity, adipose tissue expands primarily by hypertrophy (enlargement of existing adipocytes) rather than hyperplasia (generation of new adipocytes via adipogenic differentiation of preadipocytes). Progressive adipocyte hypertrophy leads to inflammation, insulin resistance, dyslipidemia, and ectopic lipid deposition, the hallmark characteristics of metabolic disease. We demonstrate that during chronic high fat feeding in mice, adipogenic differentiation is impaired due to the actions of histone deacetylase 9 (HDAC9), a member of the class II family of HDACs. Mechanistically, upregulated HDAC9 expression blocks the adipogenic differentiation program during chronic high fat feeding, leading to accumulation of improperly differentiated adipocytes with diminished expression of adiponectin. These adipocytes are inefficient at storing lipid, resulting in ectopic lipid deposition in the liver. HDAC9 gene deletion prevents the detrimental effects of chronic high fat feeding on adipogenic differentiation, increases adiponectin expression, and enhances energy expenditure by promoting beige adipogenesis, thus leading to reduced body mass and improved metabolic homeostasis. HDAC9 is therefore emerging as a critical regulator of adipose tissue health and a novel therapeutic target for obesity-related disease.