Kennedy disease, a degenerative disorder characterized by androgen-dependent neuromuscular weakness, is caused by a CAG/glutamine tract expansion in the androgen receptor (Ar) gene. We developed a mouse model of Kennedy disease, using gene targeting to convert mouse androgen receptor (AR) to human sequence while introducing 113 glutamines. AR113Q mice developed hormone and glutamine length-dependent neuromuscular weakness characterized by the early occurrence of myopathic and neurogenic skeletal muscle pathology and by the late development of neuronal intranuclear inclusions in spinal neurons. AR113Q males unexpectedly died at 2-4 months. We show that this androgen-dependent death reflects decreased expression of skeletal muscle chloride channel 1 (CLCN1) and the skeletal muscle sodium channel α-subunit, resulting in myotonic discharges in skeletal muscle of the lower urinary tract. AR113Q limb muscles show similar myopathic features and express decreased levels of mRNAs encoding neurotrophin-4 and glial cell line-derived neurotrophic factor. These data define an important myopathic contribution to the Kennedy disease phenotype and suggest a role for muscle in non-cell autonomous toxicity of lower motor neurons.

Pathways regulating neuronal vulnerability are poorly understood, yet are central to identifying therapeutic targets for degenerative neurological diseases. Here, we characterize mechanisms underlying neurodegeneration in Niemann-Pick type C (NPC) disease, a lysosomal storage disorder characterized by impaired cholesterol trafficking. To date, the relative contributions of neuronal and glial defects to neuron loss are poorly defined. Using gene targeting, we generate Npc1 conditional null mutant mice. Deletion of Npc1 in mature cerebellar Purkinje cells leads to an age-dependent impairment in motor tasks, including rotarod and balance beam performance. Surprisingly, these mice did not show the early death or weight loss that are characteristic of global Npc1 null mice, suggesting that Purkinje cell degeneration does not underlie these phenotypes. Histological examination revealed the progressive loss of Purkinje cells in an anterior-to-posterior gradient. This cell autonomous neurodegeneration occurs in a spatiotemporal pattern similar to that of global knockout mice. A subpopulation of Purkinje cells in the posterior cerebellum exhibits marked resistance to cell death despite Npc1 deletion. To explore this selective response, we investigated the electrophysiological properties of vulnerable and susceptible Purkinje cell subpopulations. Unexpectedly, Purkinje cells in both subpopulations displayed no electrophysiological abnormalities prior to degeneration. Our data establish that Npc1 deficiency leads to cell autonomous, selective neurodegeneration and suggest that the ataxic symptoms of NPC disease arise from Purkinje cell death rather than cellular dysfunction.

The neurodegenerative disorder spinal and bulbar muscular atrophy or Kennedy disease is caused by a CAG trinucleotide repeat expansion within the androgen receptor (AR) gene. The resulting expanded polyglutamine tract in the N-terminal region of the receptor renders AR prone to ligand-dependent misfolding and formation of oligomers and aggregates that are linked to neuronal toxicity. How AR misfolding is influenced by post-translational modifications, however, is poorly understood. AR is a target of SUMOylation, and this modification inhibits AR activity in a promoter context-dependent manner. SUMOylation is up-regulated in response to multiple forms of cellular stress and may therefore play an important cytoprotective role. Consistent with this view, we find that gratuitous enhancement of overall SUMOylation significantly reduced the formation of polyglutamine-expanded AR aggregates without affecting the levels of the receptor. Remarkably, this effect requires SUMOylation of AR itself because it depends on intact AR SUMOylation sites. Functional analyses, however, indicate that the protective effects of enhanced AR SUMOylation are not due to alterations in AR transcriptional activity because a branched protein structure in the appropriate context of the N-terminal region of AR is necessary to antagonize aggregation but not for inhibiting AR transactivation. Remarkably, small ubiquitin-like modifier (SUMO) attenuates AR aggregation through a unique mechanism that does not depend on critical features essential for its interaction with canonical SUMO binding motifs. Our findings therefore reveal a novel function of SUMOylation and suggest that approaches that enhance AR SUMOylation may be of clinical use in polyglutamine expansion diseases.Spinal and bulbar muscular atrophy (SBMA), 2 or Kennedy disease, is an inherited degenerative disorder of lower motor neurons (1, 2). SBMA is characterized by muscle cramps and fasciculations followed by progressive weakness and atrophy of the proximal limb and bulbar muscles (3-5). The causative genetic alteration is an expansion in the length of a CAG trinucleotide repeat within the coding sequence of the androgen receptor (AR) gene, leading to an expanded polyglutamine tract in the N-terminal transcriptional regulatory domain of the receptor. A similar expansion within the coding sequence of a set of additional genes is responsible for other members of the polyglutamine class of protein folding diseases (6, 7), which include Huntington disease, several autosomal dominant spinocerebellar ataxias (SCAs) (8), and dentatorubral-pallidoluysian atrophy (9, 10).The length of the CAG repeat within AR is correlated to the severity of SBMA. Although the normal repeat length is highly polymorphic and ranges between 9 and 36 copies, overt disease is associated with lengths in the range of 38 -62 repeats. The presence of an expanded polyglutamine tract within AR renders the protein prone to hormone-dependent misfolding, oligomerization, and aggregation and to the formation of microscopica...

An unresolved question in the study of the polyglutamine neurodegenerative disorders is the extent to which partial loss of normal function of the mutant protein contributes to the disease phenotype. To address this , we studied Kennedy disease , a degenerative disorder of lower motor neurons caused by a CAG/glutamine expansion in the androgen receptor (Ar) gene. Signs of partial androgen insensitivity , including testicular atrophy and decreased fertility , are common in affected males , although the underlying mechanisms are not well understood. Here , we describe a knock-in mouse model that reproduces the testicular atrophy , diminished fertility , and systemic signs of partial androgen insensitivity that occur in Kennedy disease patients. Using this model , we demonstrate that the testicular pathology in this disorder is distinct from that mediated by loss of AR function. Testes pathology in 113 CAG knock-in mice was characterized by morphological abnormalities of germ cell maturation , decreased solubility of the mutant AR protein , and alterations of the Sertoli cell cytoskeleton , changes that are distinct from those produced by AR loss-offunction mutation in testicular feminization mutant mice. Our data demonstrate that toxic effects of the mutant protein mediate aspects of the Kennedy disease phenotype previously attributed to a loss

Kennedy's disease is a degenerative disorder of motor neurons caused by the expansion of a glutamine tract near the amino terminus of the androgen receptor (AR). Ligand binding to the receptor is associated with several post-translational modifications, but it is poorly understood whether these affect the toxicity of the mutant protein. Our studies now demonstrate that mutation of lysine residues in wild-type AR that are normally acetylated in a ligand-dependent manner mimics the effects of the expanded glutamine tract on receptor trafficking, misfolding, and aggregation. Mutation of lysines 630 or 632 and 633 to alanine markedly delays ligand-dependent nuclear translocation. The K632A/K633A mutant also undergoes ligand-dependent misfolding and aggregation similar to the expanded glutamine tract AR. This acetylation site mutant exhibits ligand-dependent 1C2 immunoreactivity, forms aggregates that co-localize with Hsp40, Hsp70, and the ubiquitin-protein isopeptide ligase (E3) ubiquitin ligase carboxyl terminus of Hsc70-interacting protein (CHIP), and inhibits proteasome function. Ligand-dependent nuclear translocation of the wild-type receptor and misfolding and aggregation of the K632A/K633A mutant are blocked by radicicol, an Hsp90 inhibitor. These data identify a novel role for the acetylation site as a regulator of androgen receptor subcellular distribution and folding and indicate that liganddependent aggregation is dependent upon intact Hsp90 function.