Role of Spexin in White Adipose Tissue Thermogenesis under Basal and Cold-Stimulated Conditions.

Spexin (SPX) is a novel adipokine that plays an emerging role in metabolic diseases due to its involvement in carbohydrate homeostasis, weight loss, appetite control, and gastrointestinal movement, among others. In obese patients, SPX plasma levels are reduced. Little is known about the relationship between SPX and white adipose tissue (WAT) thermogenesis. Therefore, the aim of the present study was to evaluate the role of SPX in this process. C57BL/6J male mice were treated or not with SPX for ten days. On day 3, mice were randomly divided into two groups: one kept at room temperature and the other kept at cold temperature (4 °C). Caloric intake and body weight were recorded daily. At the end of the protocol, plasma, abdominal (epididymal), subcutaneous (inguinal), and brown AT (EAT, IAT, and BAT, respectively) depots were collected for measurements. We found that SPX treatment reduced Uncoupling protein 1 levels in WAT under both basal and cold conditions. SPX also reduced cox8b and pgc1α mRNA levels and mitochondrial DNA, principally in IAT. SPX did not modulate the number of beige precursors. SPX decreased spx levels in IAT depots and galr2 in WAT depots. No differences were observed in the BAT depots. In conclusion, we showed, for the first time, that SPX treatment in vivo reduced the thermogenic process in subcutaneous and abdominal AT, being more evident under cold stimulation.

Role of glucocorticoid receptor (GR) in white adipose tissue beiging.

AIM: Glucocorticoids (GCs) play a crucial role in energy homeostasis including white adipose tissue function; however, chronic GC excess is detrimental to mammals' health. White hypertrophic adiposity is a main factor for neuroendocrine-metabolic dysfunctions in monosodium L-glutamate (MSG)-damaged hypercorticosteronemic rat. Nevertheless, little is known about the receptor path in endogenous GC impact on white adipose tissue-resident precursor cells to bring them into beige lineage. Thus, our aim was to explore whether transient/chronic endogenous hypercorticosteronemia affects browning capacity in white adipose tissue pads from MSG rats during development. MAIN METHODS: Control and MSG male rats aged 30 and 90 days were 7-day exposed to cold conditions in order to stimulate wet white epidydimal adipose tissue (wEAT) beiging capacity. This procedure was also replicated in adrenalectomized rats. KEY FINDINGS: Data indicated that whereas epidydimal white adipose tissue pads from prepubertal hypercorticosteronemic rats retained full expression of GR/MR genes resulting in a drastic reduction in wEAT beiging capacity, conversely, chronic hypercorticosteronemic adult MSG rats developed down-regulation of corticoid genes (and reduced GR cytosolic mediators) in wEAT pads and consequently partially restored local beiging capacity. Finally, wEAT pads from adrenalectomized rats revealed up-regulation of GR gene accompanied by full local beiging capacity. SIGNIFICANCE: This study strongly supports a GR-dependent inhibitory effect of GC excess on white adipose tissue browning, an issue strongly supporting a key role of GR in the non-shivering thermogenic process. As a consequence, normalizing the GC milieu could be a relevant factor to handle dysmetabolism in white hyperadipose phenotypes.