Signaling Pathways for Germ Cell Death in Adult Cynomolgus Monkeys (Macaca fascicularis) Induced by Mild Testicular Hyperthermia and Exogenous Testosterone Treatment1

Abstract

Male contraception has focused, to a great extent, on approaches that induce azoospermia or severe oligospermia through accelerated germ cell apoptosis. Understanding the specific steps in the germ cell apoptotic pathways that are affected by male contraceptives will allow more specific targeting in future contraceptive development. In this study, we have used a nonhuman primate model to characterize the key apoptotic pathway(s) in germ cell death after mild testicular hyperthermia, hormonal deprivation, or combined interventions. Groups of 8 adult (7- to 10-year-old) cynomolgus monkeys (Macaca fascicularis) received one of the following treatments: 1) two empty silastic implants; 2) two 5.5-cm testosterone (T) implants; 3) daily exposure of testes to heat (43 degrees C for 30 min) for 2 consecutive days; and 4) two T implants plus testicular heat exposure for two consecutive days. Testicular biopsies were performed before and at Days 3, 8, and 28 of treatment. Treatment with T, heat, or both led to sustained activation of both mitogen-activated protein kinase (MAPK) 1/3 and MAPK14. Activation of MAPK1/3 and MAPK14 were accompanied by an increase in B-cell leukemia/lymphoma (BCL) 2 levels in both cytosolic and mitochondrial fractions of testicular lysates (BAX levels remained unaffected) and cytochrome c and DIABLO release from mitochondria. These treatments also resulted in inactivation of BCL2 through phosphorylation at serine 70, thereby favoring the death pathway. We conclude that the serine phosphorylation of BCL2 and activation of the MAPK14-mediated mitochondria-dependent pathway are critical for male germ cell death in monkeys.

Molecular basis of cryptorchidism-induced infertility

“…The subcellular redistribution of Bax and the increase in Bcl-2 expression in heat-treated testes suggest an involvement of Bcl-2 family members in heat-induced germ-cell apoptosis [45]. Our in vivo experiments also demonstrated that the heat-induced changes in the expression of caspase 2 [46], nitric oxide synthase [47] and various heat shock proteins (HSP) [48] in the testis of adult monkeys were all reversible [49]. HSP70-2 expression was almost unchanged at an early stage of germ cell apoptosis in the cryptorchid testis on day 5, and dropped dramatically, along with loss of apoptotic germ cells on day 10 after the procedure.…”

Supraphysiological Testosterone Levels Shorten the QT Interval but do Not Alter Total Anatomic Myocardial Infarct Size in Rabbits with Acute Myocardial Infarction

“…Despite the evidence suggesting that T increases apoptotic cell death, [17][18][19][20] the present study suggests that the use of exogenous testosterone at supra physiological levels is safe regarding MI size, area of no-reflow and post-MI cardiac function. This study also suggests that supra physiological levels of testosterone may in fact be beneficial in the scope of creating an anti-arrhythmia setting by shortening the QTc interval.…”

“…Some studies suggest positive cardiovascular effects of testosterone with regards to QT segment duration [12][13][14] and that higher testosterone levels are associated with a lower risk of cardiac mortality [15] and better functional capacity [16]. However, other evidence suggests that testosterone exerts a negative impact on the cardiovascular system with regards to apoptosis [17][18][19][20] and adverse cardiac events [21].…”

Male germ cell apoptosis: regulation and biology

“…Blockade of caspase 2 activation prevents heat-induced germ cell apoptosis in rats by suppressing the MAPK14 ( Johnson et al 2008;Li et al 2009a,b). Serine phosphorylation of Bcl-2 and activation of the MAPK14-mediated mitochondria-dependent pathway are critical for heat-induced male germ cell death in monkeys ( Jia et al 2007). …”