Recently our research has focused on three neuromuscular diseases: spinal and bulbar muscular atrophy (SBMA) due to polyglutamine expansion in the androgen receptor (AR), autosomal recessive spinal muscular atrophy (SMA) due to deficiency of the protein SMN, and amyotrophic lateral sclerosis type 4 (ALS4) due to mutation in senataxin. Specific research accomplishments include the following: (1) SBMA belongs to a family of polyglutamine (polyQ) diseases, which are caused by protein-mediated toxic gain-of-function mechanisms. The neurotoxicity of the polyQ diseases proteins can be modified by phosphorylation at specific sites, thereby providing a rationale for the development of disease-specific treatments. We sought to identify signaling pathways that modulate polyQ-AR phosphorylation for therapy development. We report that cyclin-dependent kinase 2 (CDK2) phosphorylates polyQ-AR specifically at Ser96. Phosphorylation of polyQ-AR by CDK2 increases protein stabilization and toxicity and is negatively regulated by the adenylyl cyclase (AC)/protein kinase A (PKA) signaling pathway. To translate these findings into therapy, we developed an analog of pituitary adenylyl cyclase activating polypeptide (PACAP), a potent activator of the AC/PKA pathway. Chronic intranasal administration of the PACAP analog to knock-in SBMA mice reduced Ser96 phosphorylation, promoted polyQ-AR degradation, and ameliorated disease outcome. These results provide proof of principle that noninvasive therapy based on the use of PACAP analogs is a therapeutic option for SBMA. (2) SBMA and other polyQ diseases are associated with proteins that because of the mutation acquire aberrant misfolded conformations. To prevent misfolded protein toxicity, cells activate a protein quality control (PQC) system composed of chaperones and degradative pathways (proteasome and autophagy). Inefficient activation of the PQC system results in misfolded protein accumulation that ultimately leads to neuronal cell death, while efficient macroautophagy/autophagy-mediated degradation of aggregating proteins is beneficial. The latter relies on an active retrograde transport, mediated by dynein and specific chaperones, such as the HSPB8-BAG3-HSPA8 complex. Using cellular models expressing aggregate-prone proteins involved in SBMA and ALS, we demonstrated that inhibition of dynein-mediated retrograde transport, which impairs the targeting to autophagy of misfolded species, does not increase their aggregation. Rather, dynein inhibition correlates with a reduced accumulation and an increased clearance of mutant ARpolyQ, SOD1, truncated TARDBP/TDP-43 and expanded polyGP C9ORF72 products. The enhanced misfolded protein clearance is mediated by the proteasome rather than by autophagy, and correlates with the upregulation of the HSPA8 cochaperone BAG1. In line, overexpression of BAG1 increases the proteasome-mediated clearance of these misfolded proteins. Our data suggest that when the misfolded proteins cannot be efficiently transported toward the perinuclear region of the cells, where they are either degraded by autophagy or stored into the aggresome, the cells activate a compensatory mechanism that relies on the induction of BAG1 to target the HSPA8-bound cargo to the proteasome in a dynein-independent manner. (3) SMA is an autosomal recessive neuromuscular disease and one of the leading inherited causes of infant mortality. Studies in animal models of SMA have shown that increasing SMN protein levels ameliorates the disease phenotype. Our group previously identified and optimized a new series of small molecules, with good potency and toxicity profiles and reasonable pharmacokinetics, that were able to increase SMN protein levels in SMA patient-derived cells. We have now shown that ML372, a representative of this series, almost doubles the half-life of residual SMN protein expressed from the SMN2 locus by blocking its ubiquitination and subsequent degradation by the proteasome. ML372 increased SMN protein levels in muscle, spinal cord, and brain tissue of SMA mice. Importantly, ML372 treatment improved the righting reflex and extended survival of a severe mouse model of SMA. These results demonstrate that slowing SMN degradation by selectively inhibiting its ubiquitination can improve the motor phenotype and lifespan of SMA model mice. (4) Astrocytes are the primary support cells of the CNS and are responsible for glutamate clearance, metabolic support, response to injury, and regulation of signal transmission. Astrocytes have been implicated in SMA as in in other neurodegenerative disorders. Astrocyte-specific rescue of SMN protein levels has been shown to mitigate disease manifestations in mice. However, the mechanism by which SMN deficiency in astrocytes may contribute to SMA is unclear and what aspect of astrocyte activity is lacking is unknown. Therefore, it is worthwhile to identify defects in SMN-deficient astrocytes that compromise normal function. We showed that SMA astrocyte cultures derived from mouse spinal cord of both sexes are deficient in supporting both WT and SMN-deficient motor neurons derived from male, female, and mixed-sex sources and that this deficiency may be mitigated with secreted factors. In particular, SMN-deficient astrocytes have decreased levels of monocyte chemoactive protein 1 (MCP1) secretion compared with controls and MCP1 restoration stimulates outgrowth of neurites from cultured motor neurons. Correction of MCP1 deficiency may thus be a new therapeutic approach to SMA.
| Bennett, Craig L; Dastidar, Somasish G; Ling, Shuo-Chien et al. (2018) Senataxin mutations elicit motor neuron degeneration phenotypes and yield TDP-43 mislocalization in ALS4 mice and human patients. Acta Neuropathol 136:425-443 |
| Guber, Robert D; Schindler, Alice B; Budron, Maher S et al. (2018) Nucleocytoplasmic transport defect in a North American patient with ALS8. Ann Clin Transl Neurol 5:369-375 |
| Fernandopulle, Michael S; Prestil, Ryan; Grunseich, Christopher et al. (2018) Transcription Factor-Mediated Differentiation of Human iPSCs into Neurons. Curr Protoc Cell Biol 79:e51 |
| Grunseich, Christopher; Wang, Isabel X; Watts, Jason A et al. (2018) Senataxin Mutation Reveals How R-Loops Promote Transcription by Blocking DNA Methylation at Gene Promoters. Mol Cell 69:426-437.e7 |
| Shi, Yingxiao; Lin, Shaoyu; Staats, Kim A et al. (2018) Haploinsufficiency leads to neurodegeneration in C9ORF72 ALS/FTD human induced motor neurons. Nat Med 24:313-325 |
| Wang, Isabel X; Grunseich, Christopher; Fox, Jennifer et al. (2018) Human proteins that interact with RNA/DNA hybrids. Genome Res 28:1405-1414 |
| Manzano, Raquel; Sorarú, Gianni; Grunseich, Christopher et al. (2018) Beyond motor neurons: expanding the clinical spectrum in Kennedy's disease. J Neurol Neurosurg Psychiatry 89:808-812 |
| Pourshafie, Naemeh; Lee, Philip R; Chen, Ke-Lian et al. (2018) Systemic Delivery of MicroRNA Using Recombinant Adeno-associated Virus Serotype 9 to Treat Neuromuscular Diseases in Rodents. J Vis Exp : |
| Plehn, Jonathan F; Hasbani, Keren; Ernst, Inez et al. (2017) The Subclinical Cardiomyopathy of Friedreich's Ataxia in a Pediatric Population. J Card Fail : |
| Guber, Robert D; Takyar, Varun; Kokkinis, Angela et al. (2017) Nonalcoholic fatty liver disease in spinal and bulbar muscular atrophy. Neurology 89:2481-2490 |
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