Leptin Induces Proadipogenic and Proinflammatory Signaling in Adipocytes

Abstract

Background: Leptin is an adipokine with well-known effects on the central nervous system including the induction of energy expenditure and satiety. Leptin also has major relevance when activating immune cells and modulating inflammatory response. In obesity, increases in white adipose tissue accumulation and leptin levels are accompanied by hypothalamic resistance to leptin. Even though the adipose tissue is a leptin-rich environment, the local actions of leptin regarding adipogenesis were not thoroughly investigated until now. Here we evaluate the contributions of leptins direct signaling in preadipocytes and adipose tissue-derived stromal cells (ASCs) for adipogenesis.Methods: Adipocytes were differentiated from the murine lineage of preadipocytes 3T3-L1 or ASCs from subcutaneous and visceral (retroperitoneal) fat depots from C57Bl/6J mice. Differentiating cells were treated with leptin in addition to or in replacement of insulin. The advance of adipogenesis was assessed by the expression and secretion of adipogenesis-and lipogenesis-related proteins by Western blot and immunoenzimatic assays, and the accumulation of lipid droplets by fluorescence microscopy.Results: Leptin treatment in 3T3-L1 preadipocytes or ASCs increased the production of the adipogenesis-and lipogenesis-related proteins PLIN1, CAV-1, PPARγ, SREBP1C, and/or adiponectin at earlier stages of differentiation. In 3T3-L1 preadipocytes, we found that leptin induced lipid droplets' formation in an mTOR-dependent manner. Also, leptin induced a proinflammatory cytokine profile in 3T3-L1 and ASCs, modulating the production of TNF-α, IL-10, and IL-6. Since insulin is considered an essential factor for preadipocyte differentiation, we asked whether leptin would support adipogenesis in the absence of insulin. Importantly, leptin induced the formation of lipid droplets and the expression of adipogenesis-related proteins independently of insulin during the differentiation of 3T3-L1 cells and ASCs. Conclusions:Our results demonstrate that leptin induces intracellular signaling in preadipocytes and adipocytes promoting adipogenesis and modulating the secretion Palhinha et al.Leptin Induces Adipogenesis of inflammatory mediators. Also, leptin restores adipogenesis in the absence of insulin. These findings contribute to the understanding of the local signaling of leptin in precursor and mature adipose cells. The proadipogenic role of leptin unraveled here may be of especial relevance during obesity, when its central signaling is defective.

Egr1loss-of-function promotes beige adipocyte differentiation and activation specifically in inguinal subcutaneous white adipose tissue

“…The beige adipocyte marker Ucp1 was not expressed either in control or mutant cells. During white adipocyte differentiation, Lep, a late marker of white adipocyte differentiation [25,26], was significantly down-regulated in mutant mASC-Egr1 -/cells compared to controls, which is consistent with the reduced white adipocyte differentiation observed in Egr1 -/cells ( Fig. 4A).…”

Egr1 loss-of-function promotes beige adipocyte differentiation and activation specifically in inguinal subcutaneous white adipose tissue

“…The beige adipocyte marker Ucp1 was not expressed either in control or mutant cells. During white adipocyte differentiation, Lep, a late marker of white adipocyte differentiation 27,28 , was significantly down-regulated in mutant mASC-Egr1 -/cells compared to controls, which is consistent with the reduced white adipocyte differentiation observed in Egr1 −/− cells (Fig. 4A).…”

Linking gene expression and phenotypic changes in the developmental and evolutionary origins of osteosclerosis in the ribs of bowhead whales (Balaena mysticetus)

“…Conversely, expression of ON, a gene associated with mineral deposition (ON; Figure 2c) showed only a twofold decline and high copy numbers (>7000; showing large copy numbers (∼15,000; Table 3). Similarly, expression of LEP, a gene associated with lipogenesis, adipogenesis (Palhinha et al, 2019), and inhibition of bone formation (Ducy et al, 2000), underwent a 19-fold increase in expression after birth with adults displaying large copy numbers (∼10,000; Table 3).…”

“…After birth, expression of EZH2 , a gene known to inhibit osteogenic pathways while upregulating adipogenic pathways by regulating differentiation of osteoprogenitor/mesenchymal stem cells (Hemming et al, 2014; Wang, Jin, Lee, Su, & Ge, 2010), increased sevenfold with the ribs of the oldest sample showing large copy numbers (∼15,000; Table 3). Similarly, expression of LEP , a gene associated with lipogenesis, adipogenesis (Palhinha et al, 2019), and inhibition of bone formation (Ducy et al, 2000), underwent a 19‐fold increase in expression after birth with adults displaying large copy numbers (∼10,000; Table 3).…”