Prenatal Flutamide Enhances Survival in a Myogenic Mouse Model of Spinal Bulbar Muscular Atrophy

Abstract

Background: Spinal bulbar muscular atrophy (SBMA) is caused by a CAG repeat expansion mutation in the androgen receptor (AR) gene, and mutant AR is presumed to act in motoneurons to cause SBMA. However, we found that mice overexpressing wild-type (wt) AR solely in skeletal muscle fibers display the same androgen-dependent disease phenotype as when mutant AR is broadly expressed, challenging the assumptions that only an expanded AR can induce disease and that SBMA is strictly neurogenic. We have previously reported that AR toxicity was ligand dependent in our model, and that very few transgenic (tg) males survived beyond birth. Methods: We tested whether the AR antagonist flutamide could block perinatal toxicity. tg males were treated prenatally with flutamide and assessed for survival and motor behavior in adulthood. Results: Prenatal treatment with flutamide rescued tg male pups from perinatal death, and, as adults, such perinatally rescued tg males showed an SBMA phenotype that was comparable to that of previously described untreated tg males. Moreover, tg males carrying a mutant endogenous allele for AR – the testicular feminization mutation (tfm) – and thus having functional AR only in muscle fibers nevertheless displayed the same androgen-dependent disease phenotype as adults. Conclusions: These mice represent an excellent model to study the myogenic contribution to SBMA as they display many of the core features of disease as other mouse models. These data demonstrate that AR acting exclusively in muscle fibers is sufficient to induce SBMA symptoms and that flutamide is protective perinatally.

Androgen-dependent loss of muscle BDNF mRNA in two mouse models of SBMA

“…Mice were genotyped using PCR at weaning as previously described (Monks et al, 2007). Tg and Wt males were exposed prenatally to flutamide, an antiandrogen, to block the effects of prenatal endogenous androgens to enhance survival rate of Tg males neonatally (Johansen et al, 2011). Because survival of Tg females is not affected, females used in our studies were from litters not exposed to flutamide prenatally.…”

“…We also assessed BDNF mRNA in lumbar spinal cords of the same Tg and Wt males of the two models. Tissue was harvested from chronically impaired myogenic males with severe motor dysfunction, comparable to what has previously been reported for this Tg model (Johansen et al, 2011; Monks et al, 2007). Tissue was harvested from 97Q males once they reached end-stage, defined as hang time < 30 sec (see description of test below).…”

“…Motor function was assessed using three different measures: number of rears in an open field, grip strength, and hang time as previously described (Johansen et al, 2011). The hang test provides a measure of overall limb strength.…”

Androgen receptors in muscle fibers induce rapid loss of force but not mass: Implications for spinal bulbar muscular atrophy

“…However, when provided with male-typical levels of testosterone, motor function of Tg females rapidly deteriorates, developing motor defects in only a few days comparable to those seen in Tg males, including shortened stride length and deficits in grip strength. 5,16 Significantly, Tg male mice with a mutation in the endogenous AR gene, which eliminates endogenous AR function, also show the same androgen-dependent loss of motor function, 17 demonstrating that testosterone activates functional transgenic AR to impair motor function. While Tg males show several markers of motoneuron disease, including atrophic and angulated muscle fibers, and deficits in the number of axons in ventral roots, acutely diseased Tg females do not.…”

Mechanisms Mediating Spinal and Bulbar Muscular Atrophy: Investigations into Polyglutamine-Expanded Androgen Receptor Function and Dysfunction

“…Neither motor neuron nor muscle fiber losses were seen, however, motor deficits were associated with androgen-dependent changes in muscle gene expression. Furthermore, the HSA-AR mice were crossed with tfm mice to generate tfm/HSA-AR mice with functional AR only in skeletal muscles (Johansen et al, 2011). The tfm/HSA-AR males had tfm -like external genitalia, undescended atrophic testis, low levels of circulating testosterone, but no signs of an SBMA phenotype.…”