PPARγ antagonists induce aromatase transcription in adipose tissue cultures

Aromatase is the rate-limiting enzyme in the biosynthesis of estrogens and a key risk factor for hormone receptor-positive breast cancer. In postmenopausal women, estrogens synthesized in adipose tissue promotes the growth of estrogen receptor positive breast cancers. Activation of peroxisome proliferator-activated receptor gamma (PPARγ) in adipose stromal cells (ASCs) leads to decreased expression of aromatase and differentiation of ASCs into adipocytes. Environmental chemicals can act as antagonists of PPARγ and disrupt its function. This study aimed to test the hypothesis that PPARγ antagonists can promote breast cancer by stimulating aromatase expression in human adipose tissue. Primary cells and explants from human adipose tissue as well as A41hWAT, C3H10T1/2, and H295R cell lines were used to investigate PPARγ antagonist-stimulated effects on adipogenesis, aromatase expression, and estrogen biosynthesis. Selected antagonists inhibited adipocyte differentiation, preventing the adipogenesis-associated downregulation of aromatase. NMR spectroscopy confirmed direct interaction between the potent antagonist DEHPA and PPARγ, inhibiting agonist binding. Short-term exposure of ASCs to PPARγ antagonists upregulated aromatase only in differentiated cells, and a similar effect could be observed in human breast adipose tissue explants. Overexpression of PPARG with or without agonist treatment reduced aromatase expression in ASCs. The data suggest that environmental PPARγ antagonists regulate aromatase expression in adipose tissue through two mechanisms. The first is indirect and involves inhibition of adipogenesis, while the second occurs more acutely.

Full activation of thermogenesis in brown adipocytes requires Basigin action

Exploring mechanisms responsible for brown adipose tissue's (BAT) high metabolic activity is crucial to exploit its energy-dissipating ability for therapeutic purposes. Basigin (Bsg), a multifunctional highly glycosylated transmembrane protein, was recently proposed as one of the 98 critical markers allowing to distinguish 'white' and 'brown' adipocytes, yet its function in thermogenic brown adipocytes is unknown. Here, we report that Bsg is negatively associated with obesity in mice. By contrast, Bsg expression increased in the mature adipocyte fraction of BAT upon cold acclimation. Additionally, Bsg levels were highly induced during brown adipocyte maturation in vitro and were further increased upon β-adrenergic stimulation in a HIF-1α-dependent manner. siRNA-mediated Bsg gene silencing in cultured brown adipocytes did not impact adipogenesis nor mitochondrial function. However, a significant decrease in mitochondrial respiration, lipolysis and Ucp1 transcription was observed in adipocytes lacking Bsg, when activated by norepinephrine. Furthermore, using gas chromatography/mass spectrometry-time-of-flight analysis to assess the composition of cellular metabolites, we demonstrate that brown adipocytes lacking Bsg have lower levels of intracellular lactate and acetoacetate. Bsg was additionally required to regulate intracellular AcAc and tricarboxylic acid cycle intermediate levels in NE-stimulated adipocytes. Our study highlights the critical role of Bsg in active brown adipocytes, possibly by controlling cellular metabolism.

Dynamic interplay between AfadinS1795 phosphorylation and diet regulates glucose homeostasis in obese mice

KEY POINTS

Afadin is a ubiquitously expressed scaffold protein with a recently discovered role in insulin signalling and glucose metabolism. Insulin-stimulated phosphorylation of Afadin at S1795 occurs in insulin-responsive tissues such as adipose tissue, muscle, liver, pancreas and heart. Afadin abundance and Afadin^S1795 phosphorylation are dynamically regulated in metabolic tissues during diet-induced obesity progression. Genetic silencing of Afadin^S1795 phosphorylation improves glucose homeostasis in the early stages of diet-induced metabolic dysregulation. Afadin^S1795 phosphorylation contributes to the early development of obesity-related complications in mice.

ABSTRACT

Obesity is associated with systemic insulin resistance and numerous metabolic disorders. Yet, the mechanisms underlying impaired insulin action during obesity remain to be fully elucidated. Afadin is a multifunctional scaffold protein with the ability to modulate insulin action through its phosphorylation at S1795 in adipocytes. In the present study, we report that insulin-stimulated Afadin^S1795 phosphorylation is not restricted to adipose tissues, but is a common signalling event in insulin-responsive tissues including muscle, liver, pancreas and heart. Furthermore, a dynamic regulation of Afadin abundance occurred during diet-induced obesity progression, while its phosphorylation was progressively attenuated. To investigate the role of Afadin^S1795 phosphorylation in the regulation of whole-body metabolic homeostasis, we generated a phospho-defective mouse model (Afadin SA) in which the Afadin phosphorylation site was silenced (S1795A) at the whole-body level using CRISPR-Cas9-mediated gene editing. Metabolic characterization of these mice under basal physiological conditions or during a high-fat diet (HFD) challenge revealed that preventing Afadin^S1795 phosphorylation improved insulin sensitivity and glucose tolerance and increased liver glycogen storage in the early stage of diet-induced metabolic dysregulation, without affecting body weight. Together, our findings reveal that Afadin^S1795 phosphorylation in metabolic tissues is critical during obesity progression and contributes to promote systemic insulin resistance and glucose intolerance in the early phase of diet-induced obesity.

The P2X7 Receptor Stimulates IL-6 Release from Pancreatic Stellate Cells and Tocilizumab Prevents Activation of STAT3 in Pancreatic Cancer Cells

Pancreatic stellate cells (PSCs) are important pancreatic fibrogenic cells that interact with pancreatic cancer cells to promote the progression of pancreatic ductal adenocarcinoma (PDAC). In the tumor microenvironment (TME), several factors such as cytokines and nucleotides contribute to this interplay. Our aim was to investigate whether there is an interaction between IL-6 and nucleotide signaling, in particular, that mediated by the ATP-sensing P2X7 receptor (P2X7R). Using human cell lines of PSCs and cancer cells, as well as primary PSCs from mice, we show that ATP is released from both PSCs and cancer cells in response to mechanical and metabolic cues that may occur in the TME, and thus activate the P2X7R. Functional studies using P2X7R agonists and inhibitors show that the receptor is involved in PSC proliferation, collagen secretion and IL-6 secretion and it promotes cancer cell migration in a human PSC-cancer cell co-culture. Moreover, conditioned media from P2X7R-stimulated PSCs activated the JAK/STAT3 signaling pathway in cancer cells. The monoclonal antibody inhibiting the IL-6 receptor, Tocilizumab, inhibited this signaling. In conclusion, we show an important mechanism between PSC-cancer cell interaction involving ATP and IL-6, activating P2X7 and IL-6 receptors, respectively, both potential therapeutic targets in PDAC.

Insulin-induced serine 22 phosphorylation of retinoid X receptor alpha is dispensable for adipogenesis in brown adipocytes

Insulin action initiates a series of phosphorylation events regulating cellular differentiation, growth and metabolism. We have previously discovered, in a mass spectrometry-based phosphoproteomic study, that insulin/IGF-1 signalling induces phosphorylation of retinoid x receptor alpha (RXRα) at S22 in mouse brown pre-adipocytes. Here, we show that insulin induces the phosphorylation of RXRα at S22 in both brown precursor and mature adipocytes through a pathway involving ERK, downstream of IRS-1 and −2. We also found that RXRα S22 phosphorylation is promoted by insulin and upon re-feeding in brown adipose tissue in vivo, and that insulin-stimulated S22 phosphorylation of RXRα is dampened by diet-induced obesity. We used Rxra knockout cells re-expressing wild type (WT) or S22A non-phosphorylatable forms of RXRα to further characterize the role of S22 in brown adipocytes. Knockout of Rxra in brown pre-adipocytes resulted in decreased lipid accumulation and adipogenic gene expression during differentiation, and re-expression of RxraWT alleviated these effects. However, we observed no significant difference in cells re-expressing the RxraS22A mutant as compared with the cells re-expressing RxraWT. Furthermore, comparison of gene expression during adipogenesis in the WT and S22A re-expressing cells by RNA sequencing revealed similar transcriptomic profiles. Thus, our data propose a dispensable role for RXRα S22 phosphorylation in adipogenesis and transcription in differentiating brown pre-adipocytes.