Biology and pathological implications of brown adipose tissue: promises and caveats for the control of obesity and its associated complications.

The discovery of metabolically active brown adipose tissue (BAT) in adult humans has fuelled the research of diverse aspects of this previously neglected tissue. BAT is solely present in mammals and its clearest physiological role is non-shivering thermogenesis, owing to the capacity of brown adipocytes to dissipate metabolic energy as heat. Recently, a number of other possible functions have been proposed, including direct regulation of glucose and lipid homeostasis and the secretion of a number of factors with diverse regulatory actions. Herein, we review recent advances in general biological knowledge of BAT and discuss the possible implications of this tissue in human metabolic health. In particular, we confront the claimed thermogenic potential of BAT for human energy balance and body mass regulation, mostly based on animal studies, with the most recent quantifications of human BAT.

Effects of alpha-lipoic acid on chemerin secretion in 3T3-L1 and human adipocytes.

Chemerin is a novel adipokine associated with obesity and insulin resistance. α-Lipoic acid (α-LA) has shown beneficial properties on diabetes and obesity. The aim of this study was to examine the effects of α-LA on chemerin production in adipocytes in absence or presence of TNF-α, insulin and AICAR. The potential signaling pathways involved in α-LA effects on chemerin were also analyzed. α-LA actions on chemerin were tested in differentiated 3T3-L1 adipocytes and in some cases in human subcutaneous and omental adipocytes. Chemerin mRNA levels were measured by RT-PCR and the amount of chemerin secreted to culture media was determined by ELISA. α-LA induced a concentration-dependent inhibition on both chemerin secretion and mRNA levels in 3T3-L1 adipocytes. The AMPK activator AICAR and the PI3K inhibitor LY294002 dramatically abrogated both chemerin secretion and gene expression, and further potentiated the inhibitory effect of α-LA on chemerin secretion. Insulin was able to partially reverse the inhibitory action of α-LA on chemerin secretion. α-LA also reduced basal chemerin secretion in both subcutaneous and omental adipocytes from overweight/obese subjects. Moreover, α-LA was able to abolish the stimulatory effects of the pro-inflammatory cytokine TNF-α on chemerin secretion. Our data demonstrated the ability of α-LA to inhibit chemerin production, an adipokine associated to obesity and metabolic syndrome, suggesting that the reduction of chemerin could contribute to the antiobesity/antidiabetic properties described for α-LA.

AGPAT2 deficiency impairs adipogenic differentiation in primary cultured preadipocytes in a non-autophagy or apoptosis dependent mechanism.

AIMS: Mutations in 1-acylglycerol-3-phosphate O-acyltransferase 2 (AGPAT2) result in lipodystrophy, insulin resistance and diabetes. Autophagy is required for normal adipogenesis and adipose tissue development. The aim of this study was to determine whether impaired autophagy or excessive cell death underlie the adipogenic inability of Agpat2(-/-) mice preadipocytes. METHODS: Preadipocytes were isolated from interscapular brown adipose tissue (BAT) of Agpat2(-/-) and Agpat2(+/+) newborn mice and cultured/differentiated in vitro. Intracellular lipids were quantified by oil red O staining. Cell death was assessed by lactate dehydrogenase (LDH) activity. Apoptosis and autophagy regulatory factors were determined at the mRNA and protein level with Real-time PCR, immunoblot and immunofluorescence. RESULTS: Adipogenically induced Agpat2(-/-) preadipocytes had fewer lipid-loaded cells and lower levels of adipocyte markers than wild type preadipocytes. Before adipogenic differentiation, autophagy-related proteins (ATGs) ATG3, ATG5-ATG12 complex, ATG7 and LC3II were increased but autophagic flux was reduced, as suggested by increased p62 levels, in Agpat2(-/-) preadipocytes. Adipogenic induction increased LDH levels in the culture media in Agpat2(-/-) preadipocytes but no differences were observed in the activation of Caspase 3 or in markers of autophagic flux. CONCLUSIONS: AGPAT2 is required for in vitro adipogenesis of mouse preadipocytes. Autophagy defects or apoptosis are not involved in the adipogenic failure of Agpat2(-/-) preadipocytes.