The rapamycin analog Everolimus reversibly impairs male germ cell differentiation and fertility in the mouse†

Abstract

Sirolimus, also known as rapamycin, and its closely-related rapamycin analog (rapalog) Everolimus inhibit ‘mammalian target of rapamycin complex 1’ (mTORC1), whose activity is required for spermatogenesis. Everolimus is FDA-approved for treating human patients to slow growth of aggressive cancers and preventing organ transplant rejection. Here, we test the hypothesis that rapalog inhibition of mTORC1 activity has a negative, but reversible, impact upon spermatogenesis. Juvenile (P20) or adult (P > 60) mice received daily injections of sirolimus or Everolimus for 30 days, and tissues were examined at completion of treatment or following a recovery period. Rapalog treatments reduced body and testis weights, testis weight/body weight ratios, cauda epididymal sperm counts, and seminal vesicle weights in animals of both ages. Following rapalog treatment, numbers of differentiating spermatogonia were reduced, with concomitant increases in the ratio of undifferentiated spermatogonia to total number of remaining germ cells. To determine if even low doses of Everolimus can inhibit spermatogenesis, an additional group of adult mice received a dose of Everolimus approximately 6-fold lower than a human clinical dose used to treat cancer. In these animals, only testis weights, testis weight/body weight ratios, and tubule diameters were reduced. Return to control values following a recovery period was variable for each of the measured parameters and was duration- and dose-dependent. Together, these data indicate rapalogs exerted a dose-dependent restriction on overall growth of juvenile and adult mice and negative impact upon spermatogenesis that were largely reversed; following treatment cessation, males from all treatment groups were able to sire offspring.

The germ cell-specific RNA binding protein RBM46 is essential for spermatogonial differentiation in mice

“…One reason for this is the relative paucity of transcriptome-wide changes [ 1 – 5 ]. In line with this, recent studies from our lab revealed RA activates the ‘mammalian target of rapamycin complex 1’ (mTORC1) kinase signaling complex, leading to enhanced translation of differentiation-required proteins such as KIT, STRA8, and SOHLH1/2 [ 6 – 9 ]. Taken together, this reveals a critical reliance upon post-transcriptional control mechanisms for gene regulation during spermatogonial differentiation.…”

Rapamycin Ameliorates Radiation-Induced Testis Damage in Mice

“…Surprisingly, male reproductive ability was recovered 12 months after sirolimus discontinuation ( Deutsch et al, 2007 ). In animal experiments, it was also reported that rapamycin damaged male reproductive ability in a dose-dependent manner under normal physiological conditions ( Kirsanov et al, 2020 ), but the testicular structure gradually returned to normal after 60 days of rapamycin withdrawal.…”

Zika virus disrupts the barrier structure and Absorption/Secretion functions of the epididymis in mice

“…Measurement of tubular diameters and epithelial thickness of epididymal duct were performed using ImageJ. Measurements of epithelial thickness and lumen diameter were performed according to previous reports [ 50 , 51 ]. Briefly, 10 samples were used to analyze epididymal tubule diameter and epithelial thickness in each group (Bilateral epididymides of 5 mice).…”