Testosterone Reduces Body Fat in Male Mice by Stimulation of Physical Activity Via Extrahypothalamic ERα Signaling.

Testosterone (T) reduces male fat mass, but the underlying mechanisms remain elusive, limiting its clinical relevance in hypogonadism-associated obesity. Here, we subjected chemically castrated high-fat diet-induced adult obese male mice to supplementation with T or the nonaromatizable androgen dihydrotestosterone (DHT) for 20 weeks. Both hormones increased lean mass, thereby indirectly increasing oxygen consumption and energy expenditure. In addition, T but not DHT decreased fat mass and increased ambulatory activity, indicating a role for aromatization into estrogens. Investigation of the pattern of aromatase expression in various murine tissues revealed the absence of Cyp19a1 expression in adipose tissue while high levels were observed in brain and gonads. In obese hypogonadal male mice with extrahypothalamic neuronal estrogen receptor alpha deletion (N-ERαKO), T still increased lean mass but was unable to decrease fat mass. The stimulatory effect of T on ambulatory activity was also abolished in N-ERαKO males. In conclusion, our work demonstrates that the fat-burning action of T is dependent on aromatization into estrogens and is at least partially mediated by the stimulation of physical activity via extrahypothalamic ERα signaling. In contrast, the increase in lean mass upon T supplementation is mediated through the androgen receptor and indirectly leads to an increase in energy expenditure, which might also contribute to the fat-burning effects of T.

Androgen action on renal calcium and phosphate handling: Effects of bisphosphonate treatment and low calcium diet.

Renal calcium and phosphate handling is an important contributor to mineral homeostasis and bone health and the androgen receptor (AR) is highly expressed in the kidney. We investigated the short term effects of androgen deprivation on renal calcium and phosphate reabsorption, independent of their effects on bone. Two weeks following orchidectomy (ORX) of adult mice, bone loss occurred along with hypercalciuria, which was similarly prevented by testosterone and dihydrotestosterone supplementation. Treatment with bisphosphonates prior to ORX also inhibited hypercalciuria, indicating that the calcium flux originated from the bone. Renal calcium and phosphate transporter expression was increased post-ORX, independent of bisphosphonates. Furthermore, androgen deprivation appeared to stimulate local synthesis of 1,25(OH)2D3. When bisphosphonate-treated mice were fed a low calcium diet, bone resorption was no longer blocked and secondary hyperparathyroidism developed, which was more pronounced in ORX mice than sham-operated mice. In conclusion, this study shows that androgen deprivation increased renal calcium and phosphate transporter expression, independent of bone, and underlines the importance of adequate intestinal calcium supply in circumstances of androgen deprivation and bisphosphonate treatment.

A shortened tamoxifen induction scheme to induce CreER recombinase without side effects on the male mouse skeleton.

The selective estrogen receptor modulator tamoxifen exerts estrogen agonistic or antagonistic actions on several tissues, including bone. The off-target effects of tamoxifen are one of the most widely recognized pitfalls of tamoxifen-inducible Cre recombinases (CreERs), potentially confounding the phenotypic findings. Still, the validation of tamoxifen induction schemes that minimize the side effects of the drug has not been addressed. Here, we compared the side effects on the skeleton and other androgen-responsive targets of a shortened tamoxifen regimen (2 doses of 190 mg/kg body weight by oral gavage) to a standard protocol (4 doses) and determined their efficiency in inducing CreER-mediated gene deletion. In addition, both a vehicle- and a 10-dose group, which served as a positive control for tamoxifen side effects, were also included. For this purpose, we generated male mice with a floxed androgen receptor (AR) and a neuron-specifically expressed CreER. Treatment with two doses of tamoxifen was the only regimen that did not diminish androgenic bioactivity, as assessed by both seminal vesicles and levator ani/bulbocavernosus muscle weights and serum testosterone concentrations. Similarly, trabecular and cortical femoral bone structure were dramatically altered by both the standard and high-dose protocols but not by the shortened version. Serum osteocalcin and bone-gene expression analyses confirmed the absence of effects on bone by 2 doses of tamoxifen. This protocol decreased AR mRNA levels efficiently and specifically in the nervous system. Thus, we optimized a protocol for tamoxifen-induced CreER gene deletion in mice without off-target effects on bone and male reproductive organs.