Expression of a K48R Mutant Ubiquitin Protects Mouse Testis from Cryptorchid Injury and Aging

Abstract

Testis injury models can be useful for determining the in vivo function of genes. In this study, ubiquitin, a tag for 26S-proteasome degradation, was mutated at lysine 48 (K48R) to inhibit ubiquitin chain assembly. K48R transgenic mice had testes with delayed germ cell loss following the acute injury of experimental cryptorchidism, and were resistant to the chronic injury of aging-associated testicular atrophy. After 4 days of cryptorchid-mediated heat stress, the average weight of cryptorchid testes in wild-type ubiquitin mice was significantly lower (P < 0.05) than in K48R mutant ubiquitin mice, indicating that altered ubiquitination delayed germ cell death. Light microscopy confirmed that the testicular injury, in both wild-type and K48R ubiquitin mice, was due to germ cell death. In addition, wild-type ubiquitin mice aged 19 to 22 months showed greater testicular atrophy and decreased average seminiferous tubule diameter when compared with K48R-aged testes. These results demonstrate a resistance to testicular injury conferred by the K48R mutation, suggesting that ubiquitin-mediated protein degradation is involved in the processing or modulation of testicular insults.

Delayed testicular aging in pituitary adenylate cyclase-activating peptide (PACAP) null mice

“…Because PACAP Ϫ/Ϫ mice have decreased P450c17 activity, we propose that testicular aging is slowed in PACAP Ϫ/Ϫ mice because of reduced steroidogenesis and the consequent reduction in ROS formation. Consistent with this hypothesis, transgenic mice exhibiting a dominant-negative mutation in ubiquitin show a testicular phenotype similar to our PACAP Ϫ/Ϫ mice due to a lack of protein degradation by the 26S-proteasome (36). In that model, the authors suggest that the level of steroidogenesis and, therefore, ROS formation is lower in these mutant mice compared with wild type, because damaged steroidogenic enzymes are not degraded.…”

The Region-Specific Functions of Two Ubiquitin C-Terminal Hydrolase Isozymes along the Epididymis

“…3 and 4A). Ubiquitin induction is important for regulating programmed cell death, which is a fundamental component of spermatogenesis [1,23,32]. Under specific circumstances, the caput epididymis contains a high level of ubiquitin, which may serve to maintain apoptotic mechanisms that eliminate abnormal spermatozoa [37].…”

The New Function of Two Ubiquitin C-Terminal Hydrolase Isozymes as Reciprocal Modulators of Germ Cell Apoptosis

“…There are several proposed mechanisms for germ cell loss following experimental cryptorchidism [28,36]. With regard to cryptorchid injury, the balance between the expression of apoptosis-protecting and apoptosisinducing proteins constitutes one possible mechanism underlying the observed germ cell protection and apoptosis from apoptosis in gad and Uchl3 knockout mice, respectively.…”