Table 2.

mRNA expression in skeletal muscle from pre-symptomatic, asymptomatic and fully symptomatic AR97Q and/or myogenic SBMA mice

Gene expression (relative to WT)		Pre- or asymptomatic Hang time = 120 s				Symptomatic Hang time < 30 s
		Males		Females		Males	Females
Models		Juvenile AR97Q	Castrated AR97Q	Control myogenic	Control AR97Q	Intact AR97Q	T-treated myogenic	T-treated AR97Q
Age (days) at time of study		29–32	55–104	101–153	64–73	55–104	101–153	64–73
N		6	8	6	4	8	6	4
Symptom onset (days)						55–104	5	14–17
AChR	ɛ	*	–	*	–	*+	*#	*#
	γ	–	*	–	*	*+	–	*
Nav	1.4	*	–	–	–	*+	*#	–
	1.5	–	*	–	*	*+	*#	*
Kir	2.1	*	–	*	*	*+	*#	*#
	2.2	–	*	–	–	*+	–	*
NKA	α1	–	*	–	*	*+	*#	*
	α2	*	–	–	–	*+	–	*#
CLCN1		*	–	–	–	*+	*#	*#

Direction of arrow indicates direction of disease-induced change relative to WT. The adult epsilon (ε) subunit is unaltered in muscle of asymptomatic adult AR97Q males (castrated pre-symptomatically) and asymptomatic AR97Q females but is affected in muscle of pre-symptomatic AR97Q males and asymptomatic myogenic females, showing a slight, yet significant decrease. As motor symptoms emerge in the presence of adult male levels of androgen, epsilon mRNA in muscle is greatly reduced, irrespective of model and sex, suggesting that the role of androgen is to exacerbate an existing deficit triggered by mutant AR independent of ligand. The AChR neonatal isoform gamma (γ) is upregulated in muscle from both diseased and asymptomatic adult AR97Q males, a defect not evident in pre-symptomatic AR97Q males. AR97Q females, both acutely diseased and asymptomatic controls, show this same increase in gamma mRNA, with a more robust increase in gamma expression in muscle from motor-impaired AR97Q females. Gamma subunit is unaffected in myogenic females. Together, these data indicate that AChR is a target of disease in SBMA contributing to synaptic dysfunction. mRNA levels for the adult Nav1.4 of the voltage-dependent sodium channel in muscle is somewhat reduced in pre-symptomatic AR97Q males but unaffected in all other groups of asymptomatic Tg mice. As motor impairments emerge, Nav1.4 mRNA becomes markedly reduced in both AR97Q males and myogenic females, but not in symptomatic AR97Q females. The neonatal isoform Nav1.5 is robustly upregulated in muscle of both symptomatic AR97Q and myogenic mice and asymptomatic AR97Q control females and adult AR97Q males castrated pre-symptomatically. These data indicate that the effect is not fully dependent on androgens. Kir2.1 mRNA encoding the Kcnj2 gene for the inward rectifying potassium channel shows a small but significant deficit in muscle of pre-symptomatic males and asymptomatic females. This deficit increases as motor symptoms emerge, suggesting that Kir2.1 expression level marks disease progression. Kir2.2 is reduced only in the AR97Q model. NKA α1 transcript encoding Atp1a1 gene for the sodium/potassium pump shows nearly the same pattern of change as AChR gamma, with small but significant increases in muscle from asymptomatic adult AR97Q mice (but not myogenic), with robust upregulation in the three symptomatic groups. NKAα2 is reduced only in the AR97Q model, indicating that this and the effect on Kir2.2 may depend on an expanded polyglutamine repeat in AR. Clcn1 transcripts are is slightly reduced in pre-symptomatic AR97Q young males and unaltered in other asymptomatic mice, but robustly and uniformly reduced in symptomatic mice of both models. This defect may be depend exclusively on androgen in SBMA because it emerges only in the present of androgens and is fully reversed in muscle of asymptomatic adult AR97Q males castrated pre-symptomatically. In summary, down-regulation of adult isoforms AChR epsilon subunit, Kir2.1 and Clcn1 and up-regulation of neonatal isoform Nav1.5 and NKA α1 consistently occur in both chronic and acutely symptomatic SBMA models, although these same genes are less altered or unaltered in pre- or asymptomatic models. These data suggest that such biomarkers are readout of androgen–dependent progression of disease in SBMA. Reduced Kir2.1 levels may be a good pre-clinical biomarker, because it could be readily examined in muscle biopsies and would shed light on the degree of muscle fiber depolarization and hence, muscle dysfunction. Significantly altered compared with their WT controls. More altered compared with their pre-symptomatic mice.

^*P < 0.05 from WT;

⁺P < 0.05 from castrated AR97Q male;

^#P < 0.05 from blank-treated female. N is the number of mice per experiment group.