Gene expression profiles in Atlantic salmon adipose-derived stromo-vascular fraction during differentiation into adipocytes

Abstract

BackgroundExcessive fat deposition is one of the largest problems faced by salmon aquaculture industries, leading to production losses due to high volume of adipose tissue offal. In addition, increased lipid accumulation may impose considerable stress on adipocytes leading to adipocyte activation and production and secretion of inflammatory mediators, as observed in mammals.ResultsMicroarray and qPCR analyses were performed to follow transcriptome changes during adipogenesis in the primary culture of adipose stromo-vascular fraction (aSVF) of Atlantic salmon. Cellular heterogeneity decreased by confluence as evidenced by the down-regulation of markers of osteo/chondrogenic, myogenic, immune and vasculature lineages. Transgelin (TAGLN), a marker of the multipotent pericyte, was prominently expressed around confluence while adipogenic PPARγ was up-regulated already in subconfluent cells. Proliferative activity and subsequent cell cycle arrest were reflected in the fluctuations of pro- and anti-mitotic regulators. Marked regulation of genes involved in lipid and glucose metabolism and pathways producing NADPH and glycerol-3-phosphate (G3P) was seen during the terminal differentiation, also characterised by diverse stress responses. Activation of the glutathione and thioredoxin antioxidant systems and changes in the iron metabolism suggested the need for protection against oxidative stress. Signs of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) occured in parallel with the increased lipid droplet (LD) formation and production of secretory proteins (adipsin, visfatin). The UPR markers XBP1 and ATF6 were induced together with genes involved in ubiquitin-proteasome and lysosomal proteolysis. Concurrently, translation was suppressed as evidenced by the down-regulation of genes encoding elongation factors and components of the ribosomal machinery. Notably, expression changes of a panel of genes that belong to different immune pathways were seen throughout adipogenesis. The induction of AP1 (Jun, Fos), which is a master regulator of stress responses, culminated by the end of adipogenesis, concurrent with the maximal observed lipid deposition.ConclusionsOur data point to an intimate relationship between metabolic regulation and immune responses in white adipocytes of a cold-blooded vertebrate. Stress imposed on adipocytes by LD formation and expansion is prominently reflected in the ER compartment and the activated UPR response could have an important role at visceral obesity in fish.

FOSL2 promotes leptin gene expression in human and mouse adipocytes

“…Stimulation of human adipocytes with dexamethasone increased both LEP and FOSL2 expression. A study on gene expression profiles in Atlantic salmon adipose-derived stromal-vascular fraction during differentiation into adipocytes reports the upregulation of AP-1 factors (c-Jun, c-Fos, JunB1, JunB2, and JunD), with a peak at the end of adipogenesis when the lipid load was the highest and genes involved in ER stress and ROS stress were also upregulated (53). Similarly, stress through serum deprivation was reported to upregulate leptin in multipotent mesenchymal stromal cells (54).…”

Exposure to lipopolysaccharide induces immune genes in cultured preadipocytes of Atlantic salmon

“…LPS treated cells stimulated expression of genes that showed co-ordinated up-regulation in the course of adipocyte differentiation, previously described by Todorcevic et al [2] (Fig. 5).…”

“…The aSVF cultures developed as previously described [2,21] and reached confluence by day 4. ICC analyses performed two days later detected very weak expression of adipocyte markers leptin and PPARg (not shown) while PPARa was seen in almost all cells (Fig.…”

“…Isolation and cultivation of aSVF cells were performed as described elsewhere [2]. In brief, fish were anesthetized with metacain (MS-222), bleeded and killed by a blow to the head.…”

“…In the basal state mammalian adipocytes produce chemokines, proand anti-inflammatory cytokines, complement components and adipokines. Our microarray profiling of adipogenesis in culture of the adipose tissue-derived stromo-vascular fraction (aSVF) of Atlantic salmon revealed regulation of a large number of immune-related genes during early (determination) and late (terminal differentiation) phases [2]. In addition to immune functions, some of these genes can be involved in the maintenance of homeostasis through modulation of proliferation and apoptosis, differentiation and metabolic functions.…”