• Tim B Koenen, Rinke Stienstra, Lambertus J van Tits, Leo A B Joosten, Jeroen F van Velzen, Anneke Hijmans, Jillis A Pol, J A van der Vliet, Mihai G Netea, Cees J Tack, Anton F H Stalenhoef, and Jacqueline de Graaf.
• Department of General Internal Medicine, Radboud University Nijmegen Medical Centre, Internal Postal Code 463, Geert Grooteplein 8, 6500 HB Nijmegen, The Netherlands. t.koenen@aig.umcn.nl
• Endocrinology. 2011 Oct 1; 152 (10): 3769-78.

AbstractThe immune competent abdominal adipose tissue, either stored viscerally [visceral adipose tissue (VAT)] or sc [sc adipose tissue (SAT)], has been identified as a source of IL-1β and IL-18. To become active, the proforms of these cytokines require processing by caspase-1, which itself is mediated by the inflammasome. In this descriptive study, we investigate the expression of inflammasome components and caspase-1 in human fat and determine whether caspase-1 activity contributes to the enhanced inflammatory status of VAT. Paired SAT and VAT biopsies from 10 overweight subjects (body mass index, 25-28 kg/m(2)) were used to study the cellular composition and the intrinsic inflammatory capacity of both adipose tissue depots. The percentage of CD8(+) T cells within the lymphocyte fraction was significantly higher in VAT compared with SAT (41.6 vs. 30.4%; P < 0.05). Adipose tissue cultures showed a higher release of IL-1β (10-fold; P < 0.05), IL-18 (3-fold; P < 0.05), and IL-6 and IL-8 (3-fold, P < 0.05; and 4-fold, P < 0.05, respectively) from VAT compared with SAT that was significantly reduced by inhibiting caspase-1 activity. In addition, caspase-1 activity was 3-fold (P < 0.05) higher in VAT compared with SAT, together with an increase in the protein levels of the inflammasome members apoptosis-associated speck-like protein containing a C-terminal caspase-recruitment domain (2-fold; P < 0.05) and nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (2-fold; nonsignificant). Finally, caspase-1 activity levels were positively correlated with the percentage of CD8(+) T cells present in adipose tissue. Our results show that caspase-1 and nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 inflammasome members are abundantly present in human VAT. The increased intrinsic caspase-1 activity in VAT represents a novel and specific inflammatory pathway that may determine the proinflammatory character of this specific depot.

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