Interleukin-2 Suppression by 2-Arachidonyl Glycerol Is Mediated through Peroxisome Proliferator-Activated Receptor γ Independently of Cannabinoid Receptors 1 and 2

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Abstract
2-Arachidonyl glycerol (2-AG) is an endogenous arachidonic acid derivative that binds cannabinoid receptors CB1 and CB2 and is hence termed an endocannabinoid. 2-AG also modulates a variety of immunological responses, including expression of the autocrine/paracrine T cell growth factor interleukin (IL)-2. The objective of the present studies was to determine the mechanism responsible for IL-2 suppression by 2-AG. Because of the labile properties of 2-AG, 2-AG ether, a nonhydrolyzable analog of 2-AG, was also used. Both 2-AG and 2-AG ether suppressed IL-2 expression independently of CB1 and CB2, as demonstrated in leukocytes derived from CB1/CB2-null mice. Moreover, we demonstrated that both 2-AG and 2-AG ether treatment activated peroxisome proliferator-activated receptor γ (PPARγ), as evidenced by forced differentiation of 3T3-L1 cells into adipocytes, induction of aP2 mRNA levels, and activation of a PPARγ-specific luciferase reporter in transiently transfected 3T3-L1 cells. Consequently, the putative role of PPARγ in IL-2 suppression by 2-AG and 2-AG ether was examined in Jurkat T cells. Concordant with PPARγ involvement, the PPARγ-specific antagonist 2-chloro-5-nitro-N-(4-pyridyl)-benzamide (T0070907) blocked 2-AG- and 2-AG ether-mediated IL-2 suppression. Likewise, 2-AG suppressed the transcriptional activity of two transcription factors crucial for IL-2 expression, nuclear factor of activated T cells and nuclear factor κB, in the absence but not in the presence of T0070907. 2-AG treatment also induced PPARγ binding to a PPAR response element in activated Jurkat T cells. Together, the aforementioned studies identify PPARγ as a novel intracellular target of 2-AG, which mediates the suppression of IL-2 by 2-AG in a manner that is independent of CB1 and/or CB2.