Androgen Receptor Gene CAG Repeat Length Varies and Affects Semen Quality in an Ethnic-Specific Fashion in Young Men from Russia

Abstract

Male infertility is a multi-factorial and multi-genetic disorder, and the prevalence of male infertility in the world is estimated at 5–35%. The search for the causes of male infertility allowed for identifying a number of genetic factors including a single X-linked gene of the androgen receptor (AR), and some of its alleles are assumed to negatively affect male fertility. Our aim was (1) to study the variability of the length of CAG repeats of the AR gene and possible associations in the AR CAG genetic variants with semen quality and reproductive hormone levels in a population-based cohort of men and (2) to estimate distributions of AR CAG repeat alleles and associations with semen parameters in different ethnic subgroups. The cohort of 1324 young male volunteers of different ethnicities (median age 23.0 years) was recruited from the general population of five cities of the Russian Federation, regardless of their fertility status. Semen quality (sperm concentration, motility and morphology), reproductive hormone levels (testosterone, estradiol, LH, FSH and inhibin B) and trinucleotide (CAG) n repeat polymorphism in exon 1 of the AR gene were evaluated. The semen samples were analyzed according to the WHO laboratory manual (WHO, 2010), serum hormones were measured by enzyme immunoassay, and the AR CAG repeat length was analyzed by direct sequencing of leukocyte DNA. The median AR CAG repeat length in men of our multi-ethnic population was 23 (range 6–39). In the entire study population, a significant difference (p ≤ 0.05) was found in the frequency distribution and the mean values for the CAG repeat length between the groups with normal (23.2 ± 3.3) and impaired semen quality (23.9 ± 3.2). Additionally, we demonstrated that the total sperm count, sperm concentration, progressive motility and normal morphology were lower in the category of long CAG repeats (CAG ≥ 25) compared with those in the category of short CAG repeats (CAG ≤ 19); however, hormonal parameters did not differ between the long and short CAG categories, with the exception of estradiol. Significant differences were observed in the AR CAG repeat length between the most common ethnic cohorts of Slavs (Caucasians), Buryats (Asians), and Yakuts (Asians). The Buryats and Yakuts had a higher number of CAG repeats than the Slavs (medians: Slavs—23; Buryats—24; Yakuts—25). The range of alleles differed among ethnicities, with the Slavs having the largest range (7–36 repeats, 24 alleles total), the Yakuts having the smallest range (18–32 repeats, 14 alleles total) and the Buryats having the middle range (11–39 repeats, 20 alleles total). The longer CAG repeats were associated with an impaired semen quality within the Slavic (CAG ≥ 25) and Buryat (CAG ≥ 28) groups, but this effect was not found in Yakuts. Hormonal parameters did not differ between the three CAG repeat categories in men of all ethnic groups. This is the largest Russian study of the distribution of AR CAG repeats and the search for association between length of AR CAG repeat tract and impaired spermatogenesis in men from the general population. Our results confirmed the association of longer CAG repeats with a risk of impaired semen quality, but this association can be modified by ethnic origin. Identification of the number of AR CAG repeats can be an effective tool to assess the risk of male subfertility and the control of androgen hormone therapy of reproductive diseases.

Effects of cigarette smoking on semen quality, reproductive hormone levels, metabolic profile, zinc and sperm DNA fragmentation in men: results from a population-based study

“…Men of three ethnic groups - Buryats, Slavs and Yakuts - were selected from our multi-ethnic study population. Our previous studies have demonstrated significant reproductive differences between these ethnic groups on semen quality, hormonal levels, and genetic factors ( 73 , 74 ). In the present study, we have shown that the proportion of smokers was the highest in the Buryat group and the lowest among the Slavs, the Yakuts occupied an intermediate position, but the smoking intensity (cigarettes per day) was the highest among the Slavs and moderate among the Buryats and Yakuts, who did not differ in this parameter.…”

“…Buryats make up 32% of the total population of Ulan-Ude, and Yakut - 43% of the total population of Yakutsk. In all cities, the study design and standardized recruitment protocol were the same, which were described earlier ( 68 , 73 , 74 ). The study included volunteers from the general population, regardless of their fertility, most of the participants were undergraduate or postgraduate students, and university staff.…”

“…Sperm concentration (million/ml), semen volume (ml), total sperm count (million/ejaculate), a proportion of morphologically normal (%) and progressively motile sperm (%), the teratozoospermia index (TZI) were analyzed according to the WHO laboratory manual for the examination and processing of human semen ( 28 ). Semen analysis was described earlier ( 68 , 73 , 74 ). The semen samples were kept at 37 0 C for 1 hr.…”

Native functions of short tandem repeats

“…PolyQ-associated nuclear translocation is also central to pathology in spinal and bulbar muscular atrophy (SBMA), where ligand binding and translocation to the nucleus of the expanded PolyQ-containing androgen receptor is required to elicit disease-associated transcriptional defects and cytotoxicity ( Katsuno et al, 2006 ; Katsuno et al, 2002 ; Montie et al, 2009 ; Palazzolo et al, 2007 ). However, within the normal range of polyQ lengths observed in humans, Androgen receptor CAG repeat size inversely correlates with the receptor’s transactivational activity and linearly correlates with infertility and decreased sperm function ( Choong and Wilson, 1998 ; Osadchuk et al, 2022 ; Pan et al, 2016 ). These findings suggest that the CAG repeats play a normal role in testosterone activated gene cascades that become aberrant at larger repeat sizes.…”

Associations of CAG repeat polymorphism in the androgen receptor gene with steroid hormone levels and anthropometrics among men: the role of the ethnic factor

“…In vitro and in vivo studies have shown that the longer the length of CAG repeats, the weaker the transactivation ability of AR and the weaker the effects of androgens in target tissues (Buchanan et al, 2004). The authors suggest that normal function of AR is maintained in a critical and limited range of CAG repeats (16-29 triplets); the number of CAG repeats outside this range can be associated with impaired function of androgen-dependent tissues and various diseases (Davis-Dao et al, 2007;Davey, Grossmann, 2016;Ryan et al, 2017;Wang et al, 2018;Osadchuk L., Osadchuk A., 2022). It should also be noted that the testosterone effects appear after it binds to AR, affecting the transcriptional activity of AR.…”