When taken together data suggest CRF plays a central role
When taken together, data suggest CRF plays a central role in linking the HPA axis, the eCB system, and the amygdala with anxiety (Hill et al., 2009, 2010a; Hillard et al., 2011). In elaborate studies in mice, Gray and colleagues (Gray et al., 2015) showed stress-associated increase in CRF concentration in the amygdala resulted in CRFR1 activation, an increase in FAAH activity, and thus decrease AEA levels. Overall, this cascade results in decreased AEA binding to CB1 receptors resulting in increased glutamate release, and increased activity of the basolateral amygdala resulting in increased expression of anxiety-like behaviors (Gray et al., 2015); this effect appeared to be independent of initial stress-related glucocorticoid increase. These data suggest one mechanism by which stress increases anxiety is via CRFR1 impacts on FAAH activity and AEA binding in the basolateral amygdala. Another recent study using a FAAH inhibitor in rats corroborates these findings (Natividad et al., 2017).
Given the relationships among the HPA axis, CRFR1, FAAH, and anxiety, we hypothesized that baseline cortisol and SNPs in CRFR1 and FAAH genes interact to influence state anxiety in humans (see Fig. 1). Here, we determined if baseline cortisol, FAAH, and CRFR1 SNPs are related to state anxiety levels, measured via the Beck Anxiety Inventory (BAI), in an aged, majority Hispanic, rural, community dwelling human population. We proposed a moderated mediation in that baseline cortisol mediates the relationship between FAAH SNP (rs324420) and state anxiety, and that effect is moderated by CRFR1 genotype. Specifically, we predict that FAAH A (AA and AC vs CC) and CRFR1 SNP minor Azithromycin Dihydrate (AA, TT, TT) will interact to predict low baseline cortisol and those individuals will have the lowest state anxiety scores. Additionally, for comparison with published data on other sample populations, we determined if baseline cortisol and any of the four SNPs are individually associated with anxiety scores, and if any of the four SNPs are related to baseline cortisol. To date, only one study, to our knowledge, has investigated the interactive effects of CRFR1 (rs110402; AA vs. GG and GA) and FAAH (rs324420; CC vs. AC and AA) genotype on anxiety-related markers in humans (Demers et al., 2016). Contrary to our predictions based on previous data (see above), using fMRI data and a moderated mediation analysis, Demers and colleagues found that individuals high in AEA signaling (FAAH AA or AC) with CRFR1 protective allele (AA vs. AG and GG) had blunted basolateral amygdala habituation and increased risk of anxiety disorders (via the DSM-IV criteria); they did not assess cortisol. Thus, it is possible that we could find results predicted by the literature outlined above, or, we may corroborate findings of Demers and colleagues and find the opposite relationship.
Discussion We found partial support for our prediction that FAAH A (AA and AC vs CC) and CRFR1 SNP minor alleles (AA, TT, TT), would interact to predict low baseline cortisol and low state anxiety scores. In CRFR1 minor carriers, the FAAH AA or AC (vs. CC) genotype was associated with higher cortisol and with lower anxiety. Additionally, in CRFR1 non-minors, those with FAAH AA or AC (vs. CC) showed decreased cortisol and higher anxiety. Based on data from this population, it seems the minor alleles of CRFR1 and the AA or AC genotype of FAAH are related to reduced anxiety, but, surprisingly, related to higher, and not lower, baseline cortisol. Additionally, among individuals with the protective CRFR1 minor combination, those with the FAAH CC genotype that confers risk had higher anxiety, but, those with the FAAH CC genotype and without the protective CRFR1 minor combination had lower anxiety. Thus, it seems the FAAH CC genotype only confers risk for anxiety in individuals who are also carriers of the CRFR1 minor combination. When dissecting our model overall, FAAH genotype was significantly associated with baseline cortisol, in that CC individuals had higher cortisol than did AA and AC individuals, which is in line with our initial predictions. But, FAAH genotype was not independently associated with anxiety, and baseline cortisol was negatively associated with anxiety score; as cortisol decreased, anxiety increased, which is contrary to our prediction. Lastly, contrary to other studies we did not find any independent relationships between any SNPs and baseline cortisol or anxiety score.