AdipoRon enhances healthspan in middle‐aged obese mice: striking alleviation of myosteatosis and muscle degenerative markers

Abstract

Background Obesity among older adults has increased tremendously. Obesity accelerates ageing and predisposes to age‐related conditions and diseases, such as loss of endurance capacity, insulin resistance and features of the metabolic syndrome. Namely, ectopic lipids play a key role in the development of nonalcoholic fatty liver disease (NAFLD) and myosteatosis, two severe burdens of ageing and metabolic diseases. Adiponectin (ApN) is a hormone, mainly secreted by adipocytes, which exerts insulin‐sensitizing and fat‐burning properties in several tissues including the liver and the muscle. Its overexpression also increases lifespan in mice. In this study, we investigated whether an ApN receptor agonist, AdipoRon (AR), could slow muscle dysfunction, myosteatosis and degenerative muscle markers in middle‐aged obese mice. The effects on myosteatosis were compared with those on NAFLD. Methods Three groups of mice were studied up to 62 weeks of age: One group received normal diet (ND), another, high‐fat diet (HFD); and the last, HFD combined with AR given orally for almost 1 year. An additional group of young mice under an ND was used. Treadmill tests and micro‐computed tomography (CT) were carried out in vivo. Histological, biochemical and molecular analyses were performed on tissues ex vivo. Bodipy staining was used to assess intramyocellular lipid (IMCL) and lipid droplet morphology. Results AR did not markedly alter diet‐induced obesity. Yet, this treatment rescued exercise endurance in obese mice (up to 2.4‐fold, P < 0.05), an event that preceded the improvement of insulin sensitivity. Dorsal muscles and liver densities, measured by CT, were reduced in obese mice (−42% and −109%, respectively, P < 0.0001), suggesting fatty infiltration. This reduction tended to be attenuated by AR. Accordingly, AR significantly mitigated steatosis and cellular ballooning at liver histology, thereby decreasing the NALFD activity score (−30%, P < 0.05). AR also strikingly reversed IMCL accumulation either due to ageing in oxidative fibres (types 1/2a, soleus) or to HFD in glycolytic ones (types 2x/2b, extensor digitorum longus) (−50% to −85%, P < 0.05 or less). Size of subsarcolemmal lipid droplets, known to be associated with adverse metabolic outcomes, was reduced as well. Alleviation of myosteatosis resulted from improved mitochondrial function and lipid oxidation. Meanwhile, AR halved aged‐related accumulation of dysfunctional proteins identified as tubular aggregates and cylindrical spirals by electron microscopy (P < 0.05). Conclusions Long‐term AdipoRon treatment promotes ‘healthy ageing’ in obese middle‐aged mice by enhancing endurance and protecting skeletal muscle and liver against the adverse metabolic and degenerative effects of ageing and caloric excess.

RORα–GABP–TFAM axis alleviates myosteatosis with fatty atrophy through reinforcement of mitochondrial capacity

“…37 Recently, efforts to enhance muscle function have focused on improving muscle quality, rather than muscle mass, which is determined by various factors including muscle fibre composition, intramuscular fat, muscle aerobic capacity and muscle fibrosis. 38,39 In the present study, administration of the RORα activator, JC1-40, reduced intramuscular lipids and restored mitochondrial function in GA muscle in a myosteatosis mouse model, which indicates that RORα activators have potential as therapeutic agents for ameliorating myosteatosis. Furthermore, JC1-40 administration significantly reduced lipid accumulation and inflammation in the liver, leading to improvement of NAFLD in a mouse model of HFD-induced NAFLD.…”

The Adiponectin Receptor Agonist, ALY688: A Promising Therapeutic for Fibrosis in the Dystrophic Muscle

“…ELISA assays allowed us to specifically detect and quantify HNE (Abcam), Myogenin, Myh7, UTRN (all from Antibodies Online, Atlanta, GA, USA), the active and phosphorylated forms of AMP-activated protein kinase (AMPK), receptor-interacting protein RIP) family of threonine/serine kinases, Smad2, p65 subunit of nuclear factor-kappa B (NF-κB) (all from Cell Signaling Technology) as well as TNFα, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and active transforming growth factor-β (TGF-β) (all from MyBiosource, San Diego, CA, USA) ( Table S3 ; [ 20 , 21 , 29 , 30 ]). Kits were based on colorimetric methods and were carried out following manufacturer’s instructions.…”

Histological Methods to Assess Skeletal Muscle Degeneration and Regeneration in Duchenne Muscular Dystrophy

“…Complementary to other recommended techniques such as mitochondrial enzymatic activity assay, bioenergetic assessments, WB, RT-qPCR or mitochondrial respirometry [137], assessing the quantity, appearance and functionality of mitochondria with histological procedures is also possible. For quantification and assessment of morphological abnormalities, transmission electron microscopy (TEM) is recommended [138,139], as general quantification by IHC or IF with antibodies to mitochondrial proteins such as cytochrome C oxidase (COX) or TOM20, although possible [140][141][142], is less precise due to the size of these organelles.…”