Actin-mediated regulation of organelle dynamics in Charcot-Marie-Tooth disease
Specifically, neurons derived from CMT patient fibroblasts and neurons from mice injected with AAVs directing expression of CMT- mutant INF2, MFN2, or RAB7A will be analyzed. Completion of these aims will provide mechanistic insight into the role of actin in organelle fission and mobility, how these processes are coupled, and test the novel hypothesis that CMT involves global disruption of mobility of multiple organelles. This will further our understanding of the pathogenic mechanism of CMT and perhaps other neurodegenerative disorders.
Investigating SIPA1L2 as a Modifier Gene and Therapeutic Target for Charcot-Marie-Tooth Type 1A
Charcot-Marie-Tooth type 1A (CMT1A) is the most common form of inherited peripheral neuropathy and there is currently no treatment. A recent human genetic study identified SIPA1L2 as a second gene that modifies the severity of CMT1A. We will use mouse models to validate the influence of SIPA1L2 on the severity of CMT1A, which could improve the accuracy of prognosis for patients, and our studies will also test whether modulating SIPA1L2 levels may be a therapeutic strategy for CMT1A, which would be a novel target for this and possibly other related neuropathies.
Project Number: 1R61NS114355-01A1 Contact PI / Project Leader: DOBROWSKY, RICK T
Title: A NOVEL PHARMACOLOGIC APPROACH TO TREAT CMT1X Awardee Organization: UNIVERSITY OF KANSAS LAWRENCE
SUMMARY Novologues are small molecule neurotherapeutics whose chemical biology is directed at modulating the activity and expression of molecular chaperones, such as heat shock protein 90 (Hsp90) and Hsp70. Over the last decade we have published rigorous pre-clinical data showing that novologues improve metabolic and clinical indices of diabetic peripheral neuropathy (DPN). Pharmacodynamically, novologues require Hsp70 for efficacy since the drugs cannot improve nerve function in diabetic Hsp70 knockout (KO) mice. KU-596 is our most clinically advanced novologue and extensive PK/PD and pre-clinical GLP toxicology studies have been accepted by the FDA. A Phase 1 trial of KU-596 has been completed and the drug showed acceptable PK/PD profiles, a negligible adverse event profile and is now poised to enter to Phase 2 trials. However, new pre-clinical data supports that the therapeutic benefit of KU-596 may also extend to certain inherited neuropathies. charcot-marie-tooth 1X (CMT1X) is an X-linked inherited neuropathy that can result from a null mutation in the gene for connexin 32 (Cx32). Cx32 deficient (Cx32def) mice are an authentic model of the human disease and our preliminary data supports that oral dosing of KU-596 improves neuromuscular function in Cx32def mice in an Hsp70-dependent manner. However, many CMT1X patients do not have a null mutation but express mutant forms of Cx32 that exhibit altered intracellular trafficking. These individuals develop a clinical neuropathy like patients with null mutations, but it is unclear whether the beneficial drug response phenotype is maintained with expression of mis-localized Cx32 mutants. Thus, the goals of this IGNITE proposal are to validate the therapeutic strengths and limitations of KU-596 in treating peripheral and CNS symptoms arising from mis-localized Cx32 mutations. Our R61 Phase will test the hypothesis that drug efficacy is maintained in T55I-Cx32def mice, which retain Cx32 in the endoplasmic reticulum (ER). We will determine if ER retention affects drug efficacy using measures of nerve conduction as the objective milestone. In the R33 phase aim 1 will identify whether improvements in markers of axonal damage correlate with the electrophysiologic recovery observed in the T55I-Cx32def mice. These data will assess whether prophylactic therapy may improve the predemyelinating axonopathy in young CMT1X patients. Aim 2 will test the hypothesis that novologue therapy decreases peripheral nerve inflammation and fulminant CNS dysfunction in Cx32def and T55I-Cx32def mice. These studies will assess the disease modifying potential of KU-596 toward reducing peripheral and central symptoms in CMT1X. Aim 3 will test the hypothesis that drug efficacy is maintained with golgi retention of Cx32. Since ER and golgi retention of Cx32 are not necessarily equivalent in their response to therapies, these data will further therapeutic advancement by broadening the breadth of CMT1X patients that may respond to KU-596. Importantly, this work has high translational impact given the lack of neurotherapeutic options for this orphan neurologic disorder and the drug’s Phase 2 readiness.
Public Health Relevance Statement:
PROJECT NARRATIVE charcot marie tooth 1X (CMT1X) is an inherited neuropathy for which there is no pharmacologic treatment. This project focuses on investigating the translational potential of a new class of small molecule therapeutics that we have developed and which may ameliorate peripheral nerve degeneration and improve the medical management of CMT1X.
Project Number: 1R21NS116936-01A1 Contact PI / Project Leader: BURGESS, ROBERT W
Title: INVESTIGATING SIPA1L2 AS A MODIFIER GENE AND THERAPEUTIC TARGET FOR CHARCOT-MARIE-TOOTH TYPE 1A Awardee Organization: JACKSON LABORATORY
PROJECT SUMMARY/ABSTRACT The goals of this project are to validate SIPA1L2 as a genetic modifier of the severity of Charcot-Marie-Tooth type 1A (CMT1A), to understand the normal function of SIPA1L2, and to determine whether modulating SIPA1L2 levels may be a therapeutic strategy for CMT1A. CMT1A is the most common form of inherited peripheral neuropathy, comprising around half of all diagnosed CMT cases, and it is caused by a genetic duplication resulting in the overexpression of peripheral myelin protein 22 (PMP22), leading to a demyelinating peripheral neuropathy. Despite the genetic reproducibility of CMT1A, the clinical severity is variable, and a recent case-only GWAS identified an association between multiple SNPs in SIPA1L2 and the severity of foot dorsiflexion in CMT1A patients. Furthermore, SIPA1L2 was found to be in the same SOX10/EGR2 gene co- expression network as other myelin genes, providing a possible mechanism for its modifier effect and suggesting that the down regulation of SIPA1L2 may be a therapeutic strategy that would result in the down regulation of PMP22, providing a novel treatment for CMT1A. However, given the low overall frequency of CMT1A, additional validation in human cohorts is a challenge, and testing the therapeutic potential of SIPA1L2 as a treatment for CMT1A requires an in vivo system modeling the demyelinating neuropathy. For this, we propose to use the established C3-PMP22 transgenic mouse model of CMT1A. In addition, we have deleted the Sipa1l2 gene from the mouse genome using CRISPR/Cas9 technology. Therefore, we are now able to use these mouse models to better understand the normal function of Sipa1l2 and to test whether changing Sipa1l2 levels will change the severity the demyelinating phenotype of the C3-PMP22 mouse model. We propose two aims. In Aim 1, we will study the loss-of-function phenotype of Sipa1l2 heterozygous and homozygous knockout mice to understand its normal function. We will use a combination of behavioral, neurophysiological and histopathological tests, focusing primarily on the neuromuscular system. We will also perform gene expression analysis by RNAseq to help define pathways that are altered by the loss of Sipa1l2, and to determine if changing Sipa1l2 levels in vivo leads to decreased expression of other myelin genes in the sciatic nerve. In Aim 2, we will combine the Sipa1l2 knockout mice with the C3-PMP22 transgenic model to determine if reducing Sipa1l2 levels changes the severity of the demyelinating phenotype. We will again use behavioral, neurophysiological and histopathological outcomes relevant to CMT1A, as well as gene expression analysis to determine the effects of Sipa1l2 in the C3-PMP22/CMT1A background. We anticipate that reducing Sipa1l2 will result in a decrease in the severity of the phenotype through reduced expression of other myelin genes. Our results to date indicate that the loss of Sipa1l2 on its own does not produce a strong phenotype, making down regulation of SIPA1L2 a more attractive strategy for treating CMT1A. The results of Aim 2 will provide an indication of the potential efficacy of such as approach.
Public Health Relevance Statement:
RELEVANCE TO PUBLIC HEALTH Charcot-Marie-Tooth type 1A (CMT1A) is the most common form of inherited peripheral neuropathy and there is currently no treatment. A recent human genetic study identified SIPA1L2 as a second gene that modifies the severity of CMT1A. We will use mouse models to validate the influence of SIPA1L2 on the severity of CMT1A, which could improve the accuracy of prognosis for patients, and our studies will also test whether modulating SIPA1L2 levels may be a therapeutic strategy for CMT1A, which would be a novel target for this and possibly other related neuropathies.