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- Materials and methods
- Supporting Information
The FK506 binding protein 51 or FKBP5 has been implicated in the regulation of glucocorticoid receptor (GR) sensitivity, and genetic variants in this gene have been associated with mood and anxiety disorders. GR resistance and associated stress hormone dysregulation are among the most robust biological findings in major depression, the extent of which may be moderated by FKBP5 polymorphisms. FKBP5 mRNA expression in peripheral blood cells (baseline and following in vivo GR stimulation with 1.5 mg dexamethasone p.o.) was analyzed together with plasma cortisol, ACTH, dexamethasone levels and the FKBP5 polymorphism rs1360780 in 68 depressed patients and 87 healthy controls. We observed a significant (P = 0.02) interaction between disease status and FKBP5 risk allele carrier status (minor allele T) on GR-stimulated FKBP5 mRNA expression. Patients carrying the risk T allele, but not the CC genotype, showed a reduced induction of FKBP5 mRNA. This FKBP5 polymorphism by disease status interaction was paralleled by the extent of plasma cortisol and ACTH suppression following dexamethasone administration, with a reduced suppression only observed in depressed patients carrying the T allele. Only depressed patients carrying the FKBP5 rs1360780 risk allele showed significant GR resistance compared with healthy controls, as measured by dexamethasone-induced FKBP5 mRNA induction in peripheral blood cells and suppression of plasma cortisol and ACTH concentrations. This finding suggests that endocrine alterations in depressed patients are determined by genetic variants and may allow identification of specific subgroups.
The FK506 binding protein 51 or FKBP5 was first described in a complex with the steroid hormone receptors 20 years ago (Sanchez 1990; Smith et al. 1990), and has emerged as one as the key players in stress-related phenotypes (Binder 2009). FKBP5 is a heat shock protein 90 (HSP90) co-chaperone which modifies steroid receptor hormone sensitivity, and interacts with the glucocorticoid receptor (GR), the progesterone receptor (PR) and the androgen receptor (AR) (Storer et al. 2011). FKBP5 is a negative regulator of GR function; when bound to the receptor complex, cortisol binds with lower affinity and the nuclear translocation of the receptor is less efficient. GR activation induces FKBP5 mRNA and protein expression and this provides an ultra-short feedback loop for GR sensitivity (Binder 2009, Jaaskelainen et al. 2011; Reynolds et al. 1999). Polymorphisms in FKBP5 have been shown to be associated with an altered induction of FKBP5 mRNA with GR activation (Binder et al. 2004) and by that interfere with the negative feedback of the stress hormone system. Individuals carrying the alleles associated with a higher induction have also been shown to have a more prolonged cortisol response to psychological stressors (Ising et al. 2008; Luijk et al. 2010), indicative of GR resistance. This altered responsiveness to stress seems to predispose to psychiatric disorders, and a number of studies have shown association of these FKBP5 polymorphisms with an increased susceptibility to major depression (Lavebratt et al. 2010; Lekman et al. 2008; Zimmermann et al. 2011; Zobel et al. 2010), bipolar disorder (Willour et al. 2008) and posttraumatic stress disorder (PTSD) (Appel et al. 2011; Binder et al. 2008; Mehta et al. 2011; Sarapas et al. 2011; Xie et al. 2010) as well as an increased suicide risk (Brent et al. 2010; Roy et al. 2012; Supriyanto et al. 2010), especially in interaction with exposure to early trauma.
In fact, a dysregulation of the stress hormone is one of the most robust biological findings in stress-related psychiatric disorders, including major depression and PTSD with changes in GR sensitivity being often reported (Binder 2009; de Kloet et al. 2005; Heim & Nemeroff 2001; Holsboer 2000; Pariante & Miller 2001). A decrease in GR sensitivity has been shown at multiple levels in patients with major depression, whereas an increase in sensitivity has been reported in patients with PTSD (Holsboer 2000; Pariante & Miller 2001; Yehuda et al. 2004) in some but not all studies.
We have recently shown that FKBP5 genotype maybe associated with biologically distinct subtypes of PTSD. In fact, only carriers of the risk alleles showed the previously described GR supersensitivity after administration of a low dose of dexamethasone, a specific agonist of the GR (Binder et al. 2008; Mehta et al. 2011). This finding was paralleled by genotype-specific gene expression changes with PTSD. In this study, we wanted to test if such FKBP5-dependent differences in GR sensitivity would also be observed in patients with major depression and could thus provide a possibility to stratify patients with depression according to biological differences. To this aim, we compared FKBP5 gene expression differences in whole blood and plasma cortisol and ACTH concentrations in healthy controls and depressed patients before and 3 h after ingestion of 1.5 mg dexamethasone in dependence of the FKBP5 single-nucleotide polymorphism (SNP) rs1360780.
- Top of page
- Materials and methods
- Supporting Information
Using an in vivo GR stimulation with dexamethasone, we found evidence that FKBP5 rs1360780 genotype status may define neuroendocrinologically distinct subtypes of major depression. The often reported impaired GR sensitivity in major depression (Holsboer 2000; Pariante & Miller 2001; Vreeburg et al. 2009) was observed only in patients carrying the FKBP5 risk allele, i.e. the minor rs1360780 T allele. This was seen using both FKBP5 mRNA induction in peripheral blood cells as well as plasma cortisol levels as a read out of GR function. These findings might explain why a perturbed HPA axis is not consistently found in patients suffering from major depression (Anacker et al. 2011; Carpenter et al. 2009; Menke et al. 2012) and supports the notion that patients with depression are different regarding underlying causal mechanisms.
While we observed genotype-dependent differences after GR stimulation, we did not observe such differences at baseline. This is in line with animal studies where transgenic mice lacking the FKBP5 gene did not exhibit significant alterations in exploratory behavior or endocrine measurements at baseline, but only after exposure to acute or chronic stressors (Hartmann et al. 2012; Touma et al. 2011).
After stimulation with dexamethasone, we observed differences in both FKBP5 mRNA induction as well as the suppression of plasma cortisol levels, both in the direction that depressed FKBP5 rs1360780 T-allele carriers, but not carriers of the protective CC genotype display GR resistance as compared with healthy controls. FKBP5 mRNA is induced by stress, including restrained stress and food deprivation in a number of tissues, including peripheral blood cells and brain and glucocorticoids mediate this effect (Menke et al. 2012,b; Scharf et al. 2011). In fact, FKBP5 mRNA induction has been proposed as a bioassay for an individual's sensitivity to glucocorticoids (Vermeer et al. 2004) and indeed, in genome-wide gene expression experiments, we could show that reduced FKBP5 mRNA induction by dexamethasone is among the 19 transcripts that most robustly predict depression status in a case/control study (Menke et al. 2012).
The fact that FKBP5 risk alleles are associated with GR resistance has been reported in a number of different studies with healthy individuals. After exposure to a psychosocial stressor, an insufficient recovery of cortisol activation was seen in a sample of healthy individuals carrying the rs1360780 risk genotype (Ising et al. 2008). Healthy volunteers with the same genotype also showed impaired dexamethasone suppression (Touma et al. 2011). On the other hand, the FKBP5 rs1360780 risk allele was associated with a reduced cortisol area under the curve sampled over 1 day in a cohort of elderly individuals (Velders et al. 2011), suggesting that there may be differential effects of the FKBP5 genotype on baseline vs. stimulated endocrine parameters. In contrast to previous studies (Binder et al. 2004, 2008; Touma et al. 2011) we did not observe genotype-dependent differences in either FKBP5 mRNA expression or cortisol levels after dexamethasone stimulation in the control group per se. This may be related to differences in the timing (11 pm vs. 6 pm) and dosage (1.5 vs. 0.5 mg) of dexamethasone administration. More detailed time and dose-response curves, possibly using ex vivo experiments, will be necessary to better characterize the effects of the FKBP5 genotype on dexamethasone-induced FKBP5 mRNA induction and cortisol suppression. In addition, differential effects of dexamethasone and the endogenous corticosteroids induced by stress exposure will need to be explored as they may have different effects on GR receptor activation.
Opposite to the findings presented here, we had previously reported that depressed patients carrying the FKBP5 risk alleles displayed a less resistant GR, as indicated by the more pronounced cortisol suppression after dexamethasone (Binder et al. 2004). In this previous sample, the dexamethasone suppression test was administered within the first 10 days of in-patient treatment, while in this study, the test was administered within the first 5 days of in-patient treatment and on average on day 3 after in-patient admission. As the same FKBP5 genotype has also been shown to be associated with better antidepressant treatment response (Binder et al. 2004; Lekman et al. 2008) and response to antidepressant treatment is associated with a normalization of GR function (Binder et al. 2009; Ising et al. 2007), we speculate that the difference in GR sensitivity in depressed patients carrying the risk allele is likely dependent on the timing after in-patient admission. Even if the difference in treatment duration between the two studies is not very large, the effect of antidepressants on GR mRNA levels has been shown to occur as early as 2.5 h after treatment (Heiske et al. 2003).
Finally, when investigating the effects of FKBP5 genotype on low-dose dexamethasone suppression in patients with PTSD, we observed an enhanced GR sensitivity in PTSD patients with the FKBP5 risk genotypes (Mehta et al. 2011), an effect opposite to the one observed among depressed patients in the sample reported here. This may be related to methodological differences in the suppression test – low dose vs. higher dose of dexamethasone, but could also be related to epigenetic effects of trauma exposure or type of disease on FKBP5 DNA methylation. In fact, exposure to glucocorticoids has been shown to lead to a demethylation of specific CpG dinucleotides flanking enhancer glucocorticoid response elements within the fkbp5 locus in mice, both in peripheral blood cells as well as neuronal and pituitary tissue (Lee et al. 2010, 2011; Yang et al. 2012). One might thus speculate that a different trauma history, i.e. different lifetime exposure to glucocorticoids, could lead to epigenetic differences in the FKBP5 locus and thus differential genotype effects (Klengel et al. 2013). A limitation of our study is the absence of data on previous trauma exposure, so that we could not consider any possible gene × environment interactions impacting the endocrine and molecular phenotypes. Another limitation is that we enrolled only Caucasians in our study. However, the effects of FKBP5 polymorphisms on other endocrine parameters and gene × environment interactions have been observed in both African-American as well as Caucasian samples (Appel et al. 2011; Binder et al. 2004, 2008; Ising et al. 2008; Klengel et al. 2013; White et al. 2012; Xie et al. 2010; Zimmermann et al. 2011), and we have identified rs1360780 as a potential causal polymorphism, leading to differences in chromatin conformation, suggesting that these effects should be observed across different ethnicities (Klengel et al. 2013).
Clinical variables such as bipolar depression, recurrent depression or suicide attempts might also impact the HPA axis (Lok et al. 2012; Manenschijn et al. 2012; Mcgirr et al. 2011) and could thus confound the interaction result. The only FKBP5 genotype-dependent clinical difference was an increase in previous suicide attempts in risk allele carriers. However, this did not confound the observed interactions on endocrine and molecular measures.
In summary, FKBP5 polymorphisms seem to impact the extent of HPA-axis dysregulation in patients with major depression. While divergent results on the direction of the effects in controls, depressed patients and patients with PTSD have been reported, all studies indicate that the FKBP5 genotype, possibly in interaction with a stressor or trauma exposure, is associated with different patterns of neuroendocrine dysregulation in stress-related psychiatric disorders. Larger, independent studies characterizing the timecourse of these interactions and possible influences of epigenetic factors are needed for a better understanding of this phenomenon.