FAAH, but not MAGL, inhibition modulates acute TLR3‐induced neuroimmune signaling in the rat, independent of sex

Lisa E. Flannery, Rebecca J. Henry, Daniel M. Kerr, David P. Finn, Michelle Roche

Toll-like receptor (TLR)3 is a key component of the innate immune response to viral infection. The present study firstly examined whether sex differences exist in TLR3-induced inflammatory, endocrine, and sickness responses. The data revealed that TLR3-induced expression of interferon- or NFkB-inducible genes (IFN-α/β, IP-10, or TNF-α), either peripherally (spleen) or centrally (hypothalamus), did not differ between male and female rats, with the exception of TLR3-induced IFN-α expression in the spleen of female, but not male, rats 8 hr post TLR3 activation. Furthermore, TLR3 activation increased plasma corticosterone levels, induced fever, and reduced locomotor activity and body weight - effects independent of sex. Thus, the acute-phase inflammatory, endocrine, and sickness responses to TLR3 activation exhibit minimal sex-related differences. A further aim of this study was to examine whether enhancing endocannabinoid tone - namely, 2-arachidonylglycerol (2-AG) or N-arachidonoylethanolamine (AEA), exhibited similar effects on TLR3-induced inflammatory responses in male versus female rats. Systemic administration of the monoacylglycerol lipase (MAGL) inhibitor MJN110 and subsequent increases in 2-AG levels did not alter the TLR3-induced increase in IP-10, IRF7, or TNF-α expression in the spleen or the hypothalamus of male or female rats. In contrast, the fatty acid amide hydrolase (FAAH) inhibitor URB597 increased levels of AEA and related N-acylethanolamines, an effect associated with the attenuation of TLR3-induced inflammatory responses in the hypothalamus, but not the spleen, of male and female rats. These data support a role for FAAH, but not MAGL, substrates in the modulation of TLR3-induced neuroinflammatory responses, effects independent of sex.