Increased PKC activity in patients with amyctrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a human neurodegenerative disorder of unknown origin which is characterized by progressive degeneration of corticospinal tracts and anterior horn cells in the brainstem and spinal cord. Previous studies have indicated that motoneuron degeneration associated with ALS may be triggered by mechanisms leading to increased intracellular calcium (Ca²⁺). In the present study, Ca²⁺-activated phospholipid-dependent protein kinase C (PKC) was evaluated in cervical spinal cords from 14 ALS patterns and 14 control subjects. In patients who died with ALS, PKC histone H1 phosphotransferase activity was significantly increased by 330% in cytosolic and 118% in particulate-derived extracts compared to control. This increase in PKC phosphotransferase activity appeared to be partially due to an increase in the amount of PKC protein present in ALS spinal cord tissue. Autophosphorylation of PKC has been reported to increase the rate of PKC histone H1 phosphotransferase activity. To determine whether autophosphorylation of PKC played a role in the mechanism underlying the increased PKC histone H1 phosphotransferase activity observed in ALS, extracts from ALS or control patients were incubated with protein phosphatase 2A (PP2A). PP2A has previously been shown to catalyze the dephosphorylation of the autophosphorylated form of PKC. Incubation with PP2A for up to 90 min had no effect on PKC histone H1 phosphotransferase activity in either ALS or control samples, suggesting that autophosphorylation does not play a role in the mechanism underlying the increased PKC activity observed in ALS patients. PKC histone H1 phosphotransferase activity also showed a tendency to be increased in particulate-derived fractions from motor cortex, another area pathologically affected in ALS. However, these increases did not reach conventional levels of statistical significance. PKC histone H1 phosphotransferase activity was not found to be significantly different in cytosolic- and paniculate-derived extracts obtained from visual cortex, an area pathologically unaffected in ALS. Non-neuronal controls, including platelets and leukocytes, showed no difference in PKC histone H1 phosphotransferase activity compared to control. The specific nature of PKC alterations in affected regions of the central nervous system support a role for PKC in the events leading to motoneuron death in sporadic ALS.