Periprostatic Adipose Tissue Displays a Chronic Hypoxic State that Limits Its Expandability

White adipose tissue accumulates at various sites throughout the body, some adipose tissue depots exist near organs whose function they influence in a paracrine manner. Prostate gland is surrounded by a poorly characterized adipose depot called periprostatic adipose tissue (PPAT), which plays emerging roles in prostate-related disorders. Unlike all other adipose depots, PPAT secretes proinflammatory cytokines even in lean individuals and does not increase in volume during obesity. These unique features remain unexplained because of the poor structural and functional characterization of this tissue. This study characterized the structural organization of PPAT in patients compared with abdominopelvic adipose tissue (APAT), an extraperitoneal adipose depot, the accumulation of which is correlated to body mass index. Confocal microscopy followed by three-dimensional reconstructions showed a sparse vascular network in PPAT when compared with that in APAT, suggesting that this tissue is hypoxic. Unbiased comparisons of PPAT and APAT transcriptomes found that most differentially expressed genes were related to the hypoxia response. High levels of the hypoxia-inducible factor 2α confirmed the presence of an adaptive response to hypoxia in PPAT. This chronic hypoxic state was associated with inflammation and fibrosis, which were not further up-regulated by obesity. This fibrosis and inflammation explain the failure of PPAT to expand in obesity and open new mechanistic avenues to explain its role in prostate-related disorders, including cancer.

Adipocyte Exosomes Promote Melanoma Aggressiveness through Fatty Acid Oxidation: A Novel Mechanism Linking Obesity and Cancer

Malignant progression results from a dynamic cross-talk between stromal and cancer cells. Recent evidence suggests that this cross-talk is mediated to a significant extent by exosomes, nanovesicles secreted by most cell types and which allow the transfer of proteins, lipids, and nucleic acids between cells. Adipocytes are a major component of several tumor microenvironments, including that of invasive melanoma, where cells have migrated to the adipocyte-rich hypodermic layer of the skin. We show that adipocytes secrete exosomes in abundance, which are then taken up by tumor cells, leading to increased migration and invasion. Using mass spectrometry, we analyzed the proteome of adipocyte exosomes. Interestingly, these vesicles carry proteins implicated in fatty acid oxidation (FAO), a feature highly specific to adipocyte exosomes. We further show that, in the presence of adipocyte exosomes, FAO is increased in melanoma cells. Inhibition of this metabolic pathway completely abrogates the exosome-mediated increase in migration. Moreover, in obese mice and humans, both the number of exosomes secreted by adipocytes as well as their effect on FAO-dependent cell migration are amplified. These observations might in part explain why obese melanoma patients have a poorer prognosis than their nonobese counterparts. Cancer Res; 76(14); 4051-7. ©2016 AACR.