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Background and Purpose: Ageing is an important risk factor of non-alcoholic fatty liver disease (NAFLD). Here, we investigated whether the deficiency of nicotinamide adenine dinucleotide (NAD(+) ), a ubiquitous coenzyme, links ageing with NAFLD.Experimental Approach: Hepatic concentrations of NAD(+) , protein levels of nicotinamide phosphoribosyltransferase (NAMPT) and several other critical enzymes regulating NAD(+) biosynthesis, were compared in middle-aged and aged mice or patients. The influences of NAD(+) decline on the steatosis and steatohepatitis were evaluated in wild-type and H247A dominant-negative, enzymically-inactive NAMPT transgenic mice (DN-NAMPT) given normal or high-fat diet (HFD).Key Results: Hepatic NAD(+) level decreased in aged mice and humans. NAMPT-controlled NAD(+) salvage, but not de novo biosynthesis pathway, was compromised in liver of elderly mice and humans. Given normal chow, middle-age DN-NAMPT mice displayed systemic NAD(+) reduction and had moderate NAFLD phenotypes, including lipid accumulation, enhanced oxidative stress, triggered inflammation and impaired insulin sensitivity in liver. All these NAFLD phenotypes, especially release of pro-inflammatory factors, Kupffer cell accumulation, monocytes infiltration, NLRP3 inflammasome pathway and hepatic fibrosis (Masson's staining and α-SMA staining), deteriorated further under HFD challenge. Oral administration of nicotinamide riboside, a natural NAD(+) precursor, completely corrected these NAFLD phenotypes induced by NAD(+) deficiency alone or HFD, whereas adenovirus-mediated SIRT1 overexpression only partially rescued these phenotypes.Conclusions and Implications: These results provide the first evidence that ageing-associated NAD(+) deficiency is a critical risk factor for NAFLD, and suggest that supplementation with NAD(+) substrates may be a promising therapeutic strategy to prevent and treat NAFLD. [ABSTRACT FROM AUTHOR]

Adipokines play important roles in metabolic homeostasis and disease. We have recently identified a novel adipokine Metrnl, also known as Subfatin, for its high expression in subcutaneous fat. Here, we demonstrate a prodifferentiation action of Metrnl in white adipocytes. Adipocyte-specific knockout of Metrnl exacerbates insulin resistance induced by high-fat diet (HFD), whereas adipocyte-specific transgenic overexpression of Metrnl prevents insulin resistance induced by HFD or leptin deletion. Body weight and adipose content are not changed by adipocyte Metrnl. Consistently, no correlation is found between serum Metrnl level and BMI in humans. Metrnl promotes white adipocyte differentiation, expandability, and lipid metabolism and inhibits adipose inflammation to form functional fat, which contributes to its activity against insulin resistance. The insulin sensitization of Metrnl is blocked by PPARγ inhibitors or knockdown. However, Metrnl does not drive white adipose browning. Acute intravenous injection of recombinant Metrnl has no hypoglycemic effect, and 1-week intravenous administration of Metrnl is unable to rescue insulin resistance exacerbated by adipocyte Metrnl deficiency. Our results suggest adipocyte Metrnl controls insulin sensitivity at least via its local autocrine/paracrine action through the PPARγ pathway. Adipocyte Metrnl is an inherent insulin sensitizer and may become a therapeutic target for insulin resistance. [ABSTRACT FROM AUTHOR]