Dynactin Deficiency in the CNS of Humans with Sporadic ALS and Mice with Genetically Determined Motor Neuron Degeneration

Dynactin is a complex motor protein involved in the retrograde axonal transport disturbances of which may lead to amyotrophic lateral sclerosis (ALS). Mice with hSOD1G93A mutation develop ALS-like symptoms and are used as a model for the disease studies. Similar symptoms demonstrate Cra1 mice, with Dync1h1 mutation. Dynactin heavy (DCTN1) and light (DCTN3) subunits were studied in the CNS of humans with sporadic ALS (SALS), mice with hSOD1G93A (SOD1/+), Dync1h1 (Cra1/+), and double (Cra1/SOD1) mutation at presymptomatic and symptomatic stages. In SALS subjects, in contrast to control cases, expression of DCTN1-mRNA but not DCTN3-mRNA in the motor cortex was higher than in the sensory cortex. However, the mean levels of DCTN1-mRNA and protein were lower in both SALS cortexes and in the spinal cord than in control structures. DCTN3 was unchanged in brain cortexes but decreased in the spinal cord on both mRNA and protein levels. In all SALS tissues immunohistochemical analyses revealed degeneration and loss of neuronal cells, and poor expression of dynactin subunits. In SOD1/+ mice both subunits expression was significantly lower in the frontal cortex, spinal cord and hippocampus than in wild-type controls, especially at presymptomatic stage. Fewer changes occurred in Cra1/SOD1 and Cra1/+ mice.It can be concluded that in sporadic and SOD1-related ALS the impairment of axonal retrograde transport may be due to dynactin subunits deficiency and subsequent disturbances of the whole dynein/dynactin complex structure and function. The Dync1h1 mutation itself has slight negative effect on dynactin expression and it alleviates the changes caused by SOD1G93A mutation.