Differential expression and localization of 12/15 lipoxygenases in adipose tissue in human obese subjects

Abstract

Adipose tissue inflammation in obesity is a major factor leading to cardiovascular disease and type 2 diabetes.12/15 lipoxygenases (ALOX) play an important role in the generation of inflammatory mediators, insulin resistance and downstream immune activation in animal models of obesity. However, the expression and roles of 12/15ALOX isoforms, and their cellular sources in human subcutaneous (sc) and omental (om) fat in obesity is unknown. The objective of this study was to examine the gene expression and localization of ALOX isoforms and relevant downstream cytokines in subcutaneous (sc) and omental (om) adipose tissue in obese humans. Paired biopsies of sc and om fat were obtained during bariatric surgeries from 24 morbidly obese patients. Gene and protein expression for ALOX15a, ALOX15b and ALOX 12 were measured by real-time PCR and western blotting in adipocytes and stromal vascular fractions (SVF) from om and sc adipose tissue along with the mRNA expression of the downstream cytokines IL-12a, IL-12b, IL-6, IFNγ and the chemokine CXCL10. In a paired analysis, all ALOX isoforms, IL-6, IL-12a and CXCL10 were significantly higher in om vs. sc fat. ALOX15a mRNA and protein expression was found exclusively in om fat. All of the ALOX isoforms were expressed solely in the SVF. Further fractionation of the SVF in CD34+ and CD34-cells indicated that ALOX15a is predominantly expressed in the CD34+ fraction including vascular and progenitor cells, while ALOX15B is mostly expressed in the CD34-cells containing various leucocytes and myeloid cells. This result was confirmed by immunohistochemistry showing exclusive localization of ALOX15a in the om fat and predominantly in the vasculature and non-adipocyte cells. Our finding is identifying selective expression of ALOX15a in human om but not sc fat. This is a study showing a major inflammatory gene exclusively expressed in visceral fat in humans.

Adipose Tissue 12/15 Lipoxygenase Pathway in Human Obesity and Diabetes

“…Mice with a targeted deletion of 12-/15-LO in adipose tissue are protected from IR and pancreatic islet inflammation, suggesting a key role of AT 12-/15-LO for the onset of IR in obesity (12). We previously reported that ALOX 12, ALOX 15A and ALOX 15B have a depot-and cell-specific expression in human AT that differs from that of animal models of obesity (6), which emphasizes the importance of findings validation in humans (1).…”

“…These procedures were described previously (6). Results were normalized to 18S RNA and data were expressed as 1/⌬ cycle threshold.…”

“…A recent paper described the presence and diversity of both the pro-and antiinflammatory lipid mediators derived from the lipoxygenase pathway in sc and perivascular fat in humans (5). We have previously demonstrated that in obese humans, ALOX 12, ALOX 15a, and ALOX 15b are more highly expressed in omental (OM) than in sc adipose tissue (AT) (6). Little is known about the upstream activators of the 12/15 ALOX enzymes in human AT.…”

The 5-lipoxygenase/leukotriene pathway in obesity, insulin resistance, and fatty liver disease

“…In-vitro studies have shown that addition of 12-lipoxygenase and 15-lipoxygenase products to adipocytes induces inflammatory adipokine secretion and impairs insulin action [25]. Finally, Dobrian et al [42], working with subcutaneous and omental tissues from morbidly obese patients, have elegantly demonstrated that 12/15-lipoxygenase is predominantly expressed in visceral fat in which it correlates with increased mRNA levels of IL-6, IL-12, interferon-g, and CXCL10.…”

15(S)-HETE-induced angiogenesis in adipose tissue is mediated through activation of PI3K/Akt/mTOR signaling pathway

“…Obesity resulting from expansion of adipose tissue is associated with low-grade inflammation, and lipoxygenase enzymes have been linked to inflammatory changes leading to the development of obesity (Ye 2009;Cole et al 2012;Dobrian et al 2010). Adipocytes express ; studies indicate overexpression of 15-LOX gene in adipocytes isolated from obese rats when compared with lean rats (Sears et al 2009;Chanez et al 2002).…”