Elevated Steroidogenesis, Defective Reproductive Organs, and Infertility in Transgenic Male Mice Overexpressing Human Chorionic Gonadotropin

Abstract

We previously developed a transgenic (TG) mouse model that overexpresses the human chorionic gonadotropin (hCG) beta-subunit under the universal human ubiquitin C promoter, displaying in males a modest 3-fold increase in circulating levels of LH/hCG bioactivity. The males were fertile and presented with a mild reproductive phenotype. To achieve higher levels of hCG, a double TG model was generated by cross-breeding the hCG beta-expressing mice with another TG line harboring a ubiquitin C/common alpha-subunit fusion gene. The double-TG mice expressed excessive levels of dimeric hCG, with 2000-fold elevated circulating LH/hCG bioactivity. These male mice were infertile, primarily due to inability to copulate, and they showed enhanced testicular androgen production despite clear down-regulation of LH/hCG receptors. Their intratesticular inhibin B was unaltered, but serum FSH was markedly reduced. Apparently the chronic hCG hyperstimulation led to focal Leydig cell proliferation/hypertrophy at 6 months of age, but failed to promote testicular tumors. Even though full spermatogenesis occurred in most of the seminiferous tubules, progressive tubule degeneration was apparent as the males grew older. The prostate and seminal vesicles were enlarged by distension of glandular lumina. Functional urethral obstruction was indicated by distension and sperm accumulation in distal vas deferens as well as by dilated urinary bladder and enlarged kidneys. The abnormal function of accessory sex glands and/or lower urinary tract as a consequence of the disturbed sex hormone balance or direct action of hCG may be the main cause of infertility in this model. The present study provides in vivo evidence that exposure of male mice to chronically elevated levels of hCG severely affects their urogenital tract function at multiple sites and causes infertility, but, unlike in LH/hCG overexpressing female mice, it is not tumorigenic.

Identification of a Unique Transgenic Mouse Line That Develops Megabladder, Obstructive Uropathy, and Renal Dysfunction

“…associated with a demyelinating peripheral neuropathy (30,31). Transgenic mice that overexpress human chorionic gonadotropin develop functional urethral obstruction that is associated with enlargement of prostates and seminal vesicles (32). None of the defects that are observed in these mice is similar to the mgbϪ/Ϫ phenotype, suggesting that the mgbϪ/Ϫ mouse is a unique transgenic model.…”

Extragonadal LH/hCG action—Not yet time to rewrite textbooks

“…In the hCGβ TG mice (hCGβ+), the hCGβ transgene is expressed also in the pituitary cells expressing the endogenous common α-subunit. This enables dimerization of the TG and endogenous subunits to form biologically active hCG (human β/mouse α-subunit), inducing 3-4 fold elevation in hCG/LH bioactivity in males, but 30-fold increase in females compared to wild-type (WT) littermates (Rulli et al, 2002;Rulli et al, 2003). Phenotypic characterization of the hCGβ+ males revealed no obvious alterations, with the exception of slightly decreased testis weights most probably due to decreased FSH-levels seen in these males .…”

“…Transgenic (TG) mice overexpressing hCGβ and common α-subunits under the human ubiquitin C promoter were produced by conventional pronuclear injection techniques (Rulli et al, 2002;Rulli et al, 2003). In these mice, the ubiquitin C promoter maintains low level TG expression in most tissue types, and its activity has been shown to start on embryonic day 10.5 (Schorpp et al, 1996).…”

Constitutively active luteinizing hormone receptors: Consequences of in vivo expression

“…In mouse models of ectopic overexpression of hCG producing very high levels of testosterone, infertility and Leydig cell hyperplasia were observed in older animals (Rulli et al, 2002;Matzuk et al, 2003;Rulli et al, 2003). Futher studies showed that although there was a significant increase in testosterone levels in hCG expressing mice as early as postnatal day 5, there was no evidence of early puberty (Ahtiainen et al, 2005).…”

“…Consequently, genetically modified mouse models with loss-offunction and gain-of-function phenotypes have been generated to elucidate the molecular mechanisms of gonadotropin action in vivo (Risma et al, 1995;Kumar et al, 1997;Dierich et al, 1998;Kumar et al, 1998;Lei et al, 2001;Zhang et al, 2001;Rulli et al, 2002;Matzuk et al, 2003;Rulli et al, 2003;Ma et al, 2004). Of all the human mutations that are known for gonadotropins and their receptors, the most reported are the activating and inactivating LHR mutations.…”