Analysis of dynein intermediate chains, light intermediate chains and light chains in a cohort of hereditary peripheral neuropathies

Genetic Neuropathy Due to Impairments in Mitochondrial Dynamics

Mitochondria are dynamic organelles capable of fusing, dividing, and moving about the cell. These properties are especially important in neurons, which in addition to high energy demand, have unique morphological properties with long axons. Notably, mitochondrial dysfunction causes a variety of neurological disorders including peripheral neuropathy, which is linked to impaired mitochondrial dynamics. Nonetheless, exactly why peripheral neurons are especially sensitive to impaired mitochondrial dynamics remains somewhat enigmatic. Although the prevailing view is that longer peripheral nerves are more sensitive to the loss of mitochondrial motility, this explanation is insufficient. Here, we review pathogenic variants in proteins mediating mitochondrial fusion, fission and transport that cause peripheral neuropathy. In addition to highlighting other dynamic processes that are impacted in peripheral neuropathies, we focus on impaired mitochondrial quality control as a potential unifying theme for why mitochondrial dysfunction and impairments in mitochondrial dynamics in particular cause peripheral neuropathy.

Silencing of Tctex1 impairs autophagy lysosomal degradation of α-synuclein and cell viability

Tctex1 is an important element of the dynein motor unit in mammalian cells that helps move targets along microtubules and toward the centrosome for degradation. Here, we analyzed the role of Tctex1 in the α-synuclein autophagy-lysosome degradation pathway using Tctex1-siRNA in SH-SY5Y cells. Results showed that siRNA silencing of Tctex1 suppressed cellular viability and promoted cell apoptosis. Protein and mRNA expression of Tctex1 and dynein decreased after Tctex1 knockdown, whereas α-synuclein, LC3-II, and LAMP2 increased. Consistently, fluorescence intensity of Tctex1 was weaker in siRNA-Tctex1-transfected cells, and that of α-synuclein, LC3-II, and LAMP2 was increased. Tctex1 inhibition reduced cell viability and promoted apoptosis. These results show that Tctex1 plays an important role in α-synuclein autophagic degradation and in maintaining cellular homeostasis.

Mutation analysis of genes within the dynactin complex in a cohort of hereditary peripheral neuropathies

The cytoplasmic dynein-dynactin genes are attractive candidates for neurodegenerative disorders given their functional role in retrograde transport along neurons. The cytoplasmic dynein heavy chain (DYNC1H1) gene has been implicated in various neurodegenerative disorders, and dynactin 1 (DCTN1) genes have been implicated in a wide spectrum of disorders including motor neuron disease, Parkinson's disease, spinobulbar muscular atrophy and hereditary spastic paraplegia. However, the involvement of other dynactin genes with inherited peripheral neuropathies (IPN) namely, hereditary sensory neuropathy, hereditary motor neuropathy and Charcot-Marie-Tooth disease is under reported. We screened eight genes; DCTN1-6 and ACTR1A and ACTR1B in 136 IPN patients using whole-exome sequencing and high-resolution melt (HRM) analysis. Eight non-synonymous variants (including one novel variant) and three synonymous variants were identified. Four variants have been reported previously in other studies, however segregation analysis within family members excluded them from causing IPN in these families. No variants of disease significance were identified in this study suggesting the dynactin genes are unlikely to be a common cause of IPNs. However, with the ease of querying gene variants from exome data, these genes remain worthwhile candidates to assess unsolved IPN families for variants that may affect the function of the proteins.