Basal mTORC2 activity and expression of its components display diurnal variation in mouse perivascular adipose tissue.

In adipose tissue mTOR complex 2 (mTORC2) contributes to the regulation of glucose/lipid metabolism and inflammatory molecule expression. Both processes display diurnal variations during the course of the day. RICTOR and mSIN1 are unique and essential components of mTORC2, which is activated by growth factors including insulin. To assess whether mTORC2 components display diurnal variations, we analyzed steady state mRNA expression levels of Rictor, mSin1, and mTor in various adipose tissues during a 24 h period. Diurnally regulated expression of Rictor was detected in brown adipose tissues displaying highest mRNA expression levels at the beginning of the 12 h light period (zeitgeber time 2, ZT2). Gene expression patterns of mSin1 and mTor displayed a similar diurnal regulation as Rictor in PVAT while smaller changes were detected for these genes in aorta during the course of the day. Basal mTORC2 activity was measured by phosphorylation of protein kinase C (PKC) α at serine 657 was higher at ZT14 as compared with ZT2 in PVAT. In line, gene expression of inflammatory molecules nitric oxide synthase 2 and tumor necrosis factor α was lower at ZT 14 compared to ZT2. Our findings provide evidence for a diurnal regulation of expression of mTORC2 components and activity. Hence, mTORC2 is possibly an integral part of diurnally regulated signaling pathways in PVAT and possibly in other adipose tissues.

Hypoxia potentiates tumor necrosis factor-α induced expression of inducible nitric oxide synthase and cyclooxygenase-2 in white and brown adipocytes.

Obesity involves hypoxic adipose tissue and low-grade chronic inflammation. We investigated the impact of hypoxia on inflammatory response to TNF-α in white and brown adipocytes. In response to TNF-α, the expression of the inducible enzymes iNOS and COX-2 was prominently and selectively potentiated during hypoxia while only moderately under normoxia. Levels of their products, nitrite and prostaglandinE2 were elevated accordingly. NS398, a selective COX-2 inhibitor, reduced nitrite levels. The expression of PGC-1α, a transcriptional co-activator involved in mitochondrial biogenesis, and PPARγ, a transcription factor involved in adipocyte homeostasis, was reduced by TNF-α during hypoxia. These results suggest that hypoxia potentiates the inflammatory response by TNF-α in both white and brown adipocytes and downregulates the transcription factors involved in adipocyte function.

Rictor in perivascular adipose tissue controls vascular function by regulating inflammatory molecule expression.

OBJECTIVE: Perivascular adipose tissue (PVAT) wraps blood vessels and modulates vasoreactivity by secretion of vasoactive molecules. Mammalian target of rapamycin complex 2 (mTORC2) has been shown to control inflammation and is expressed in adipose tissue. In this study, we investigated whether adipose-specific deletion of rictor and thereby inactivation of mTORC2 in PVAT may modulate vascular function by increasing inflammation in PVAT. APPROACH AND RESULTS: Rictor, an essential mTORC2 component, was deleted specifically in mouse adipose tissue (rictor(ad-/-)). Phosphorylation of mTORC2 downstream target Akt at Serine 473 was reduced in PVAT from rictor(ad-/-) mice but unaffected in aortic tissue. Ex vivo functional analysis of thoracic aortae revealed increased contractions and impaired dilation in rings with PVAT from rictor(ad-/-) mice. Adipose rictor knockout increased gene expression and protein release of interleukin-6, macrophage inflammatory protein-1α, and tumor necrosis factor-α in PVAT as shown by quantitative real-time polymerase chain reaction and Bioplex analysis for the cytokines in the conditioned media, respectively. Moreover, gene and protein expression of inducible nitric oxide synthase was upregulated without affecting macrophage infiltration in PVAT from rictor(ad-/-) mice. Inhibition of inducible nitric oxide synthase normalized vascular reactivity in aortic rings from rictor(ad-/-) mice with no effect in rictor(fl/fl) mice. Interestingly, in perivascular and epididymal adipose depots, high-fat diet feeding induced downregulation of rictor gene expression. CONCLUSIONS: Here, we identify mTORC2 as a critical regulator of PVAT-directed protection of normal vascular tone. Modulation of mTORC2 activity in adipose tissue may be a potential therapeutic approach for inflammation-related vascular damage.