GABA SYNTHESIS BY CULTURED FIBROBLASTS OBTAINED FROM PERSONS WITH HUNTINGTON'S DISEASE1

Abstract

Abstract— A consistent observation in particular regions of brains of persons having died with Huntington's disease (HD) is a reduction in the concentration of γ‐aminobutyric acid (GABA) and a decrease in the activity of its synthetic enzyme, glutamate decarboxylase (EC 4.1.4.15). GABA levels are also reduced in HD cerebrospinal fluids. This study suggests that skin fibroblasts obtained from persons with HD can be used to study their GABA system. A rapid and specific assay for [14C]glutamate– [14C]GABA based on Aminex A‐7 chromatography has been developed. Cell monolayers and homogenates of HD cells convert [14C]glutamate to [14C]GABA. GABA synthesis by HD cell homogenates is pyridoxal dependent and is inhibited by 1 mm‐aminooxyacetic acid. GABA synthesis by HD and control cell homogenates also show the same thermal sensitivity as rat brain GAD. When compared to non‐HD human cells the HD cells reveal disturbances in the non‐neuronal GABA metabolic pathway. Concentrated HD cell homogenates synthesize approx 3 times the amount of GABA as control cells. When diluted both extracts made similar amounts of GABA. Synthesis of GABA by HD cell homogenates is not inhibited by cysteine sulfinate. Decarboxylation of glutamate in these cells is therefore most likely due to glutamate decarboxylase and not cysteine sulfinate decarboxylase. HD cells in monolayer also synthesize 3 times the amount of GABA as compared to control cells. In addition, glutamate upake is altered in HD cells. This report indicates there may be a different pattern of enzyme regulation between HD and control cells.