Background: Individuals with spinal muscular atrophy (SMA) III walk independently, but experience muscle weakness, gait impairments, and fatigue. Although SMA affects proximal more than distal muscles, the characteristic pattern of selective muscle weakness has not been explained. Two theories have been proposed: 1) location of spinal motor neurons; and 2) differences in segmental innervation. Objective: To identify neuroanatomical models that explain the selective muscle weakness in individuals with SMA and assess the relationship of these models to ambulatory function. Methods: Data from 23 ambulatory SMA participants (78.2% male), ages 10–56 years, enrolled in two clinical studies (NCT01166022, NCT02895789) were included. Strength was assessed using the Medical Research Council (MRC) score; ambulatory function was measured by distance walked on the 6-minute walk test (6 MWT). Three models were identified, and relationships assessed using Pearson correlation coefficients and linear regression. Results: All models demonstrated a positive association between strength and function, (p < 0.02). Linear regression revealed that Model 3B, consisting of muscles innervated by lower lumbar and sacral segments, explained 67% of the variability observed in 6 MWT performance (β= 0.670, p = 0.003). Conclusions: Muscles innervated by lower lumbar and sacral segments, i.e. hip extensors, hip abductors, knee flexors and ankle dorsiflexors, correlated with and predicted greater ambulatory function. The neuroanatomical patterns of muscle weakness may contribute to a better understanding of disease mechanisms and enable delivery of targeted therapies.
Metabolic reprogramming is a common hallmark shared by nearly all proliferating cancer cells, and thus has emerged as an exciting new direction in cancer research. Many signaling pathways have been implicated in mechanisms leading to the shift of metabolic programs in tumors, but more recently a small number of metabolic enzymes have also been identified in this process. Genes encoding the metabolic enzymes Isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) were found to be mutated in up to 70% of low-grade and medium grade gliomas, and in 15-20% of adult acute leukemia samples. These findings were the first to link the IDH gene to tumorigenesis. IDH1 and IDH2 function to irreversibly catalyze the oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG). We are studying how mutations in IDH affect the metabolism and cellular processes of the cell. To this end, we have expressed IDH-R132H in Drosophila glial cells and hemoctyes to learn more about the impact of neomorphic activity of IDH in gliobastoma and chronic myeloid leukemia. We have verified that these cells now produce 2-HG, as is known in human tumors harboring IDH mutations. We have observed different cellular responses to IDH mutations in glia versus hemoctyes and have begun to investigate why this may be. Ultimately, the goal of our research is to elucidate the mechanism(s) that cause IDH to contribute to oncogenic activity in specific tissues, and use this knowledge to design tailored therapeutics. Citation Format: Julia Fabiano, Gabriela Chiaramida, Mira Magner, Meghan O'Connor, Joseph Stallone, Nicholas DiDuca, Kathryn Neville, Richard Tartarini, Marla Tipping. Using Drosophila to study the role of metabolic enzyme mutations in glioblastoma and leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1827. doi:10.1158/1538-7445.AM2017-1827
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