Activin receptor ALK4 promotes adipose tissue hyperplasia by suppressing differentiation of adipocyte precursors

Cellular Senescence and Extracellular Vesicles in the Pathogenesis and Treatment of Obesity-A Narrative Review

This narrative review explores the pathophysiology of obesity, cellular senescence, and exosome release. When exposed to excessive nutrients, adipocytes develop mitochondrial dysfunction and generate reactive oxygen species with DNA damage. This triggers adipocyte hypertrophy and hypoxia, inhibition of adiponectin secretion and adipogenesis, increased endoplasmic reticulum stress and maladaptive unfolded protein response, metaflammation, and polarization of macrophages. Such feed-forward cycles are not resolved by antioxidant systems, heat shock response pathways, or DNA repair mechanisms, resulting in transmissible cellular senescence via autocrine, paracrine, and endocrine signaling. Senescence can thus affect preadipocytes, mature adipocytes, tissue macrophages and lymphocytes, hepatocytes, vascular endothelium, pancreatic β cells, myocytes, hypothalamic nuclei, and renal podocytes. The senescence-associated secretory phenotype is closely related to visceral adipose tissue expansion and metaflammation; inhibition of SIRT-1, adiponectin, and autophagy; and increased release of exosomes, exosomal micro-RNAs, pro-inflammatory adipokines, and saturated free fatty acids. The resulting hypernefemia, insulin resistance, and diminished fatty acid β-oxidation lead to lipotoxicity and progressive obesity, metabolic syndrome, and physical and cognitive functional decline. Weight cycling is related to continuing immunosenescence and exposure to palmitate. Cellular senescence, exosome release, and the transmissible senescence-associated secretory phenotype contribute to obesity and metabolic syndrome. Targeted therapies have interrelated and synergistic effects on cellular senescence, obesity, and premature aging.

Human ACVR1C missense variants that correlate with altered body fat distribution produce metabolic alterations of graded severity in knock-in mutant mice

BACKGROUND & AIMS

Genome-wide studies have identified three missense variants in the human gene ACVR1C, encoding the TGF-β superfamily receptor ALK7, that correlate with altered waist-to-hip ratio adjusted for body mass index (WHR/BMI), a measure of body fat distribution.

METHODS

To move from correlation to causation and understand the effects of these variants on fat accumulation and adipose tissue function, we introduced each of the variants in the mouse Acvr1c locus and investigated metabolic phenotypes in comparison with a null mutation.

RESULTS

Mice carrying the I195T variant showed resistance to high fat diet (HFD)-induced obesity, increased catecholamine-induced adipose tissue lipolysis and impaired ALK7 signaling, phenocopying the null mutants. Mice with the I482V variant displayed an intermediate phenotype, with partial resistance to HFD-induced obesity, reduction in subcutaneous, but not visceral, fat mass, decreased systemic lipolysis and reduced ALK7 signaling. Surprisingly, mice carrying the N150H variant were metabolically indistinguishable from wild type under HFD, although ALK7 signaling was reduced at low ligand concentrations.

CONCLUSION

Together, these results validate ALK7 as an attractive drug target in human obesity and suggest a lower threshold for ALK7 function in humans compared to mice.

lpla (lipoprotein lipase a) is a marker of early adipogenesis rather than late adipogenesis in grass carp (Ctenopharyngodon idellus)

Lipoprotein lipase (LPL) functions as a marker of adipocyte differentiation in mammals, but little is known about its role in fish adipogenesis. The aim of this research is to investigate the function of Lpl in adipocyte differentiation in fish. In this paper, we isolated and characterized lipoprotein lipase a (lpla) and lipoprotein lipase b (lplb) from grass carp (Ctenopharyngodon idellus). The complete coding sequence of lpla and lplb was 1524 bp and 1503 bp in length, coding for 507 amino acids and 500 amino acids, respectively. Both lpla and lplb mRNA were expressed in a great number of tissues. During adipogenesis, the level of lpla mRNA reached its maximum at day 2 and then dropped gradually, while the level of lplb mRNA had no significant changes, indicating that lpla and lplb may have different function in the differentiation of grass carp adipocyte. Furthermore, inhibition of lpla by inhibitor of LPL(GSK264220A) at early time points most clearly reduced adipogenesis, whereas these effects were less pronounced at later stages, suggesting that lpla predominantly affects early adipogenesis rather than late adipogenesis. Based on these findings, it can be inferred that lpla and lplb in grass carp may have distinct roles in the differentiation of grass carp adipocyte, and lpla may play an important role in the early adipogenesis rather than late adipogenesis in grass carp.