Elevated Testosterone Induces Apoptosis in Neuronal Cells

Abstract

Testosterone plays a crucial role in neuronal function, but elevated concentrations can have deleterious effects. Here we show that supraphysiological levels of testosterone (micromolar range) initiate the apoptotic cascade. We used three criteria, annexin V labeling, caspase activity, and DNA fragmentation, to determine that apoptotic pathways were activated by testosterone. Micromolar, but not nanomolar, testosterone concentrations increased the response in all three assays of apoptosis. signals lead to apoptotic cell death. These effects of testosterone on neurons will have long term effects on brain function.Neurosteroids have been implicated as components essential for the normal function of the central nervous system (1-4). The gonadal steroid hormones are required for reproductive function, but androgens also affect areas of the brain that are not primarily involved in reproduction such as the hippocampus (5), preoptic area, amygdala, and medial hypothalamic area (6). At physiological levels, androgens are involved in neuronal differentiation, neuroprotection, neuronal survival and development (7-9). These responses occur slowly (over hours) and are mediated through the intracellular androgen receptor. In the developing brain, androgens are capable of changing the ultrastructural characteristics of the neuronal plasma membrane with a relatively fast pace (10, 11). Recently, we have shown that nanomolar levels of testosterone induce rapid intracellular Ca 2ϩ increases in neuroblastoma cells (within seconds), which begin as Ca 2ϩ transients in the cytosol, propagate as waves of Ca 2ϩ in the cytoplasm and nucleus, and develop into an oscillatory pattern (12). These Ca 2ϩ signals depend on an interplay between Ca 2ϩ efflux from the endoplasmic reticulum through inositol 1,4,5-trisphosphate-sensitive Ca 2ϩ release channels (InsP 3 Rs) 4 and Ca 2ϩ reuptake into the endoplasmic reticulum by Ca 2ϩ pumps. This new testosterone-induced pathway in neuronal cells leads to neurite outgrowth (12), an essential event in neuronal differentiation (13). These results suggest an important physiological mechanism for the action of testosterone in neurons at physiological concentrations. However, it is unknown how these cells respond to high plasma levels of this neurosteroid, generally administered exogenously to achieve an increase in muscle mass (14, 15) or for replacement therapy (16). In vivo administration of large doses of androgens has been correlated with neurobehavioral changes like hyperexcitability, supra-aggressive nature, and suicidal tendencies (17, 18). These behavioral changes could be the outward manifestation of neuronal damage resulting from exposure to high concentrations of testosterone.In this investigation, we evaluated the hypothesis that high concentrations of testosterone can induce deleterious effects in neurons. We show that high levels of testosterone initiate an apoptotic program in neuroblastoma cells. Apoptosis is the normal and controlled process of cell death (19). Precise control of apoptos...

Non-genomic actions of androgens

“…The receptor mediating these protective effects is thought to be AR due to the fact that AR antagonists block the neuroprotective effects [163; 164]. In contrast, supraphysiological levels of T have been found to increase neuronal apoptosis [165]. In fact, the damage-promoting effects of T have been observed in several experimental models.…”

Vocal Cord Paralysis Secondary to Anabolic Steroid Abuse

“…Studies have demonstrated AAS to be neurotoxic when injected in the proximity of peripheral nerves [27]. Although the exact mechanism by which this occurs is poorly understood, it is postulated that AAS initiate the apoptotic cascade of neuronal cells [28]. …”

Neurophysiological Repercussions of Anabolic Steroid Abuse: A Road into Neurodegenerative Disorders

“…Long-term administration of nandrolone decanoate results in increased activation of caspase-3 and apoptosis throughout hippocampal and cortical structures [79]. Several in vitro studies have also demonstrated that exposure of neuroblastoma cells, primary hippocampal cells, and pheochromocytoma cells to AS can result in increased activation of caspase-3 [15,80,81]. Caspase-3 can be activated in both extrinsic and intrinsic apoptosis pathways and exerts a pivotal role in the execution of the apoptotic process by proteolytic cleavage of several proteins and chromatin condensation, resulting in DNA fragmentation and other changes throughout the apoptotic process.…”

“…Interestingly, in neuroblastoma cell culture, exposure to testosterone-induced concentrationdependent sustained increase in intracellular calcium concentration that involved up-regulation of inositol-triphosphate receptor (InsP 3 R) type I-induced calcium release [15]. As demonstrated elsewhere, prolonged calcium overload can trigger apoptosis in several cell types [83].…”

“…Exposure of neuroblastoma cells to testosterone resulted in concentration-dependent increase of intracellular calcium in a time range of 50-100 sec [15]. Interestingly, knock down or blockade of endoplasmic reticulum IP 3 receptor (InsP 3 R) abolished the testosterone-induced increase on intracellular calcium concentration, suggesting that InsP 3 R-mediated testosterone effect [15].…”