Two isoforms of glutamate decarboxylase: why?

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Adults express two glutamate decarboxylase (GAD) isoforms: GAD67 and GAD65.
• These isoforms are encoded by independently regulated genes, unlike other neurotransmitter systems.
• Both GAD67 and GAD65 are found in most GABA-containing neurons in the central nervous system (CNS).

Purpose of the Study:

• To review current knowledge on the differences between GAD67 and GAD65.
• To elucidate the distinct cellular localization and functional roles of GAD67 and GAD65.
• To explore the implications of isoform-specific functions in GABA-ergic neurotransmission.

Main Methods:

• Literature review of existing research on GAD isoforms.
• Analysis of studies investigating GAD65 and GAD67 localization within neurons.
• Examination of evidence regarding the preferential synthesis and targeting of GABA by each isoform.

Main Results:

• GAD65 is primarily targeted to membranes and nerve endings, while GAD67 exhibits broader cellular distribution.
• GAD67 may preferentially synthesize cytoplasmic GABA, whereas GAD65 might favor GABA synthesis for vesicular release.
• Evidence suggests distinct roles for GAD67 and GAD65 in information coding by GABA-ergic neurons.

Conclusions:

• GAD67 and GAD65, despite both synthesizing GABA, possess distinct subcellular localizations and potentially specialized functions.
• These isoform-specific properties indicate differential contributions to GABAergic neurotransmission and neuronal signaling.
• Understanding these differences is crucial for comprehending the complex roles of GABA in the CNS.