Major depressive disorder (MDD) is more prevalent in HIV type 1 than in noninfected individuals1,2 and, in particular, in women.3 Prevalent rates for depressive disorders can vary depending on the use of illicit substances.4 Moreover, a positive correlation between depression and HIV disease progression has been demonstrated.5 Depression can also be associated with the progression of cognitive impairment.6 These considerations underscore the importance of characterizing the molecular mechanisms that underlie HIV-mediated depression.
Clinical studies of mood disorder patients have provided evidence for neuronal atrophy/loss in limbic brain structures. For instance, brain imaging and postmortem studies have demonstrated a reduction in the volume7 and atrophy of neurons in limbic brain regions implicated in MDD.8,9 These data correlate with decreased levels of neurotrophic factors in MDD patients and, in particular, brain-derived neurotrophic factor (BDNF) in both the hippocampus10 and serum.11,12 BDNF is a secreted neurotrophic factor that is critical for numerous aspects of synaptic plasticity in the adult central nervous system, including hippocampal neurogenesis.13 Most importantly, BDNF produces antidepressant responses in animal models of depression.14 Thus, it has been widely accepted that alterations in BDNF expression and/or signaling contribute to depressive symptoms. However, there is much less evidence relating BDNF signaling to depressive symptoms in the presence of HIV.
HIV promotes a reduction in BDNF levels, but HIV-infected individuals may exhibit depression irrespective of their levels of BDNF.15,16 Conversely, BDNF fosters neuronal plasticity by binding to a receptor complex formed by TrkB, the tyrosine kinase receptor (coded by NTRK2), and a low-affinity receptor, p75NTR.17 Given the physiological role of these receptors in the trophic activity of BDNF, we investigated possible associations of single-nucleotide polymorphisms (SNPs) in these genes with depression susceptibility in HIV-positive subjects. To our knowledge, there are no HIV-control studies exploring the relevance of SNPs in genes encoding for BDNF receptors in depression. Because the incidence of MDD in women is greater than men,18 we examined the frequency of these SNPs in the Women’s Interagency HIV Study (WIHS) cohort and analyzed their distributions as functions of self-reported depression status and race.
MATERIALS AND METHODS
Genomic DNA samples were obtained from WIHS. The cohort is representative of women with HIV in the United States, mirroring the epidemic among women ethnically, sociodemographically, and by risk group categories.19 Women were enrolled at 6 consortium sites nationally: Bronx/Manhattan and Brooklyn in New York City, Los Angeles, San Francisco, Chicago, and Washington, DC. Samples comprised 321 HIV-negative and 1109 HIV-positive African Americans (non-Hispanic), and 50 HIV-negative and 256 HIV-positive Caucasians (non-Hispanic), with a mean age of 50.6 years for Caucasians and 50 years for African Americans. Both cohorts were followed up between years 1994 and 2007. Center for Epidemiologic Study Depression Scale (CES-D) cutoff scores of 16 (see Ref. 20) were used to characterize subjects as “depressed” (CES-D ≥ 16) or not (CES-D < 16). Educational level, employment status, and history of illicit drugs (self-reported) did not interfere with CES-D scores. All WIHS participants signed consent forms at the beginning of the study that explicitly included language related to ancillary studies such as this one. All participants were assigned a unique identifier number for anonymity on all data sheets and laboratory requests. The study was approved by the Georgetown University Institutional Review Board. All key research personnel have certification for protection of human subjects as mandated by the Institutional Review Board.
Single-Nucleotide Polymorphisms Genotyping
Genomic DNA was extracted from blood samples using the QIAamp DNA Blood Mini Kit (Qiagen Inc, Valencia, CA). rs56164415, rs1212171, and rs2072446 genotyping were performed using a TaqMan 5-exonuclease allelic discrimination assay according to the instructions provided by the manufacturer (Applied Biosystems, Foster City, CA). The ABI 7900 (Applied Biosystems) multiplex real-time polymerase chain reaction machine was used for this analysis. Genotyping success rate was 98.4%, and no deviation from Hardy–Weinberg was noted.
Associations between CES-D depression status and allele frequencies were estimated using the χ2 test. P < 0.05 was considered to be statistically significant individually for each inference (no multiple comparisons corrections were employed after the Fisher least significance difference approach). Logistic regression was carried out to obtain estimates of the shared variability between depression status and genotype. All analyses were done in SPSS v 20.x (IBM Inc, Armonk, NY).
Association of Allelic Polymorphisms and Depressive Symptoms in HIV-Positive and -Negative Subjects
To examine associations between depressive symptoms and allele distributions of rs1212171 (TrkB), rs2072446 (p75NTR), and rs56164415 (BDNF) polymorphisms, we first estimated them in the HIV-negative cohort. Because of their different genetic backgrounds, African American and white groups were analyzed independently. There were no significant associations between rs1212171, rs2072446, or rs56164415 allele distribution and depressive symptoms in the HIV-negative subjects of either race (all P > 0.3; data not shown).
We then examined allelic distribution of rs1212171, rs2072446, and r56164415 in HIV-positive subjects. The χ2 test revealed significant differences in allelic distribution of rs1212171 between those classified as having versus not having depressive symptoms, in white non-Hispanic subjects (P = 0.013) and African American non-Hispanic (P = 0.011) subjects (Table 1). No associations between rs2072446 (p75NTR) or rs56164415 (BDNF) and depressive symptoms were detected in HIV-positive individuals of either race (all P > 0.12; data not shown).
Assessment of Contribution of rs1212171, rs2072446, and rs56164415 to Depressive Symptoms in HIV-Positive Subjects
To assess the importance of BDNF, TrkB, and p75NTR SNPs in depressive symptomatology among HIV-positive women in our cohort, we obtained Nagelkerke’s generalized coefficient of determination (NR2) through logistic regressions of each allele on depressive symptoms (CES-D < 16 or CES-D ≥ 16) first separately by race and then collapsed over race. As expected from the χ2 test results, rs1212171 had a statistically significant association with the absence of depressive symptoms in HIV-positive subjects (Table 2) by race (both P ≤ 0.015) and collapsed across race (data not shown). The NR2 values were 0.008 and 0.044 for African Americans and Caucasians, respectively, suggesting that the presence of this mutation explains 0.8% and 4.4% of the variability, respectively, in the absence of depressive symptoms (CES-D < 16) among HIV-positive women.
BDNF, through its tyrosine kinase receptor TrkB, evokes antidepressant responses in animal models of depression.14 In addition, low levels of BDNF in humans have been associated with mood-related behaviors.21 Thus, many investigators have implicated BDNF in the pathogenesis of depression, suggesting that BDNF could be explored as an avenue for the treatment of clinical depression. HIV and its glycoprotein gp120 have been shown to decrease the expression of BDNF in both human16 and rat brains,22 suggesting that reduced BDNF levels could have a role in HIV-mediated depression. However, studies on the relationship between BDNF SNPs and MDD23 have been inconclusive. Moreover, little is known about SNPs in the TrkB (rs1212171) and p75NTR (rs2072446) genes, which encode for 2 receptors essential for all neurotrophic properties of BDNF. The data presented here show significant differences in allelic distribution of rs1212171 in HIV-infected white and African American non-Hispanic women without depression. As shown in Table 1, the frequency of allele C is about equal to that of allele T in HIV-positive subjects with depressive symptoms but allele C is far more prevalent than allele T in HIV-positive individuals without depressive symptoms. Although not significant, this same pattern was observed in the HIV-negative individuals of both races (data not shown). Thus, it seems that lower likelihood of T alleles and greater likelihood of C alleles may have a positive effect against depressive symptoms.
SNP variations in genes can reveal genetic influences in diseases and genetic markers to predict response to drugs and adverse drug reactions. Such variations may also contribute to differences in susceptibilities to comorbidities such as MDD in individuals with different ethnic backgrounds. The BDNF gene exhibits several SNPs, the most frequent are dinucleotide repeat polymorphisms in the promoter region, including a common G to A polymorphism (rs6265), which leads to a change of valine to methionine at position 196 of the BDNF gene.24 In previous studies, we have analyzed this SNP and found no association between rs6265 and BDNF serum levels in HIV-positive women.15 Here, we present that there is also no association between another SNP, rs56164415, which is located near the 5′ end of the BDNF gene, and depressive symptoms in a large cohort. These results suggest that these 2 SNPs are unlikely candidates for protection against depressive symptomatology in HIV-positive women.
Because BDNF regulates synaptic plasticity through its TrkB receptor, we investigated whether genetic variations in this gene may be associated with self-reported depression. Our study focused on a SNP in the 5′UTR of the TrkB gene. SNPs in this promoter region are more likely to be associated with general stability of the RNA transcript rather than regulation of alternative splicing. In addition, the NTRK2 gene contains putative target sites for microRNAs.25 MicroRNAs are noncoding RNAs that function as inhibitors of mRNA translation.26 Thus, this SNP may alter microRNA target sites in the nontranslated regions of NTRK2. Our results suggest that haplotype distribution of the TrkB SNP differs significantly in HIV-positive women with and without self-reported depression, independent of race. Specifically, our data indicate that subjects with depressive symptoms are characterized by approximately equal distribution of C and T alleles, whereas individuals without depressive symptoms carry C alleles in far greater proportions than the T allele. Moreover, the relationship between rs1212171 and a lack of depression symptoms in HIV-positive females is statistically significant, for both non-Hispanic Caucasians (4.4% shared variability) and African American (0.8% shared variability).
We also examined the association between self-reported depression and rs2072446, a Ser205Leu missense polymorphism in the p75 NTR. This SNP has been suggested to exert a protective effect against the development of MDD in a cohort of female Japanese subjects.27 Our data suggest no association between this SNP and depressive symptoms in either HIV-positive or -negative women. However, the genetic background of our samples differs from those used in previous studies, as does our definition of depressed, which was not based on a clinical diagnosis of MDD. Thus, our results cannot speak to the role of the Leu205 allele in MDD. In addition, among HIV-positive individuals, those with major neurological problems exhibit higher amounts of pro-BDNF than those without neurological impairments.16 Pro-BDNF is the larger glycosylated BDNF precursor that evokes p75NTR-mediated neuronal atrophy and death.28 These phenomena are particularly noticeable when the activation of p75NTR is not balanced by a concomitant stimulation of TrkB29 or by an altered mBDNF/proBDNF ratio, both of which are observed in HIV-positive subjects.16 Thus, a functional p75NTR in HIV subjects would compromise synaptic connections and neuronal survival.
In conclusion, we have identified a genetic variant of NTRK2 in Caucasians and African Americans with an association with the absence of depression in HIV-positive women. The clinical significance of this finding with respect to the expression of TrkB protein remains to be fully characterized. C to T mutation in the 5′UTR may affect methylation that is crucial for RNA transcription. In addition, NTRK2 encodes for a truncated TrkB that may act as a dominant negative isoform.30 Thus, additional studies are warranted to determine the influence of this SNP on RNA transcription/stability. Moreover, we have used samples from women only, and studies should be extended to men as well.
1. Castellon SA, Hardy DJ, Hinkin CH, et al.. Components of depression in HIV-1
infection: their differential relationship to neurocognitive performance. J Clin Exp Neuropsychol. 2006;28:420–437.
2. Owe-Larsson B, Sall L, Salamon E, et al.. HIV infection and psychiatric illness. Afr J Psychiatry (Johasnnesbg). 2009;12:115–128.
3. Morrison MF, Petitto JM, Ten Have T, et al.. Depressive and anxiety disorders in women with HIV infection. Am J Psychiatry. 2002;159:789–796.
4. Goggin K, Engelson ES, Rabkin JG, et al.. The relationship of mood, endocrine, and sexual disorders in human immunodeficiency virus positive (HIV+) women: an exploratory study. Psychosom Med. 1998;60:11–16.
5. Ickovics JR, Hamburger ME, Vlahov D, et al.. Mortality, CD4 cell count decline, and depressive symptoms among HIV-seropositive women: longitudinal analysis from the HIV Epidemiology Research Study. JAMA. 2001;285:1466–1474.
6. Wojna V, Nath A. Challenges to the diagnosis and management of HIV dementia. AIDS Read. 2006;16:615–616, 621–614, 626, 629–632.
7. Drevets WC, Price JL, Furey ML. Brain structural and functional abnormalities in mood disorders: implications for neurocircuitry models of depression. Brain Struct Funct. 2008;213:93–118.
8. Krishnan V, Nestler EJ. The molecular neurobiology of depression. Nature. 2008;455:894–902.
9. Miguel-Hidalgo JJ, Rajkowska G. Morphological brain changes in depression: can antidepressants reverse them? CNS Drugs. 2002;16:361–372.
10. Chen B, Dowlatshahi D, MacQueen GM, et al.. Increased hippocampal BDNF
immunoreactivity in subjects treated with antidepressant medication. Biol Psychiatry. 2001;50:260–265.
11. Shimizu E, Hashimoto K, Okamura N, et al.. Alterations of serum levels of brain-derived neurotrophic factor (BDNF
) in depressed patients with or without antidepressants. Biol Psychiatry. 2003;54:70–75.
12. Karege F, Perret G, Bondolfi G, et al.. Decreased serum brain-derived neurotrophic factor levels in major depressed patients. Psychiatry Res. 2002;109:143–148.
13. Cotman CW, Berchtold NC. Exercise: a behavioral intervention to enhance brain health and plasticity. Trends Neurosci. 2002;25:295–301.
14. Duman RS, Voleti B. Signaling pathways underlying the pathophysiology and treatment of depression: novel mechanisms for rapid-acting agents. Trends Neurosci. 2012;35:47–56.
15. Avdoshina V, Garzino-Demo A, Bachis A, et al.. HIV-1
decreases the levels of neurotrophins in human lymphocytes. AIDS. 2011;25:1126–1128.
16. Bachis A, Avdoshina V, Zecca L, et al.. Human immunodeficiency virus type 1 alters brain-derived neurotrophic factor processing in neurons. J Neurosci. 2012;32:9477–9484.
17. Chao MV. Neurotrophins and their receptors: a convergence point for many signalling pathways. Nat Rev Neurosci. 2003;4:299–309.
18. Gilchrist G, Blazquez A, Torrens M. Psychiatric, behavioural and social risk factors for HIV infection among female drug users. AIDS Behav. 2011;15:1834–1843.
19. Bacon MC, von Wyl V, Alden C, et al.. The Women's Interagency HIV Study: an observational cohort brings clinical sciences to the bench. Clin Diagn Lab Immunol. 2005;12:1013–1019.
20. Radloff LS. The CES-D scale. Appl Psychol Meas. 1977;1:385–401.
21. Post RM. Role of BDNF
in bipolar and unipolar disorder: clinical and theoretical implications. J Psychiatr Res. 2007;41:979–990.
22. Nosheny RL, Bachis A, Acquas E, et al.. Human immunodeficiency virus type 1 glycoprotein gp120 reduces the levels of brain-derived neurotrophic factor in vivo: potential implication for neuronal cell death. Eur J Neurosci. 2004;20:2857–2864.
23. Kocabas NA, Antonijevic I, Faghel C, et al.. Brain-derived neurotrophic factor gene polymorphisms: influence on treatment response phenotypes of major depressive disorder. Int Clin Psychopharmacol. 2011;26:1–10.
24. Cargill M, Altshuler D, Ireland J, et al.. Characterization of single-nucleotide polymorphisms in coding regions of human genes. Nat Genet. 1999;22:231–238.
25. Maussion G, Yang J, Yerko V, et al.. Regulation of a truncated form of tropomyosin-related kinase B (TrkB) by Hsa-miR-185* in frontal cortex of suicide completers. PLoS One. 2012;7:e39301.
26. Bartel DP. MicroRNAs: target recognition and regulatory functions. Cell. 2009;136:215–233.
27. Fujii T, Yamamoto N, Hori H, et al.. Support for association between the Ser205Leu polymorphism of p75(NTR) and major depressive disorder. J Hum Genet. 2011;56:806–809.
28. Teng HK, Teng KK, Lee R, et al.. ProBDNF induces neuronal apoptosis via activation of a receptor complex of p75NTR and sortilin. J Neurosci. 2005;25:5455–5463.
29. Yang J, Siao CJ, Nagappan G, et al.. Neuronal release of proBDNF. Nat Neurosci. 2009;12:113–115.
30. Dorsey SG, Renn CL, Carim-Todd L, et al.. In vivo restoration of physiological levels of truncated TrkB.T1 receptor rescues neuronal cell death in a trisomic mouse model. Neuron. 2006;51:21–28.