Voltage-Gated Calcium Channel Dysfunction in Human Diseases

Familial Hemiplegic migraine type-1 (FHM1) and incomplete congenital night blindness (CSNB2) are human diseases resulting from mutations in different genes of voltage-gated calcium channels. Similar to targeted mutations in mice, these diseases represent unique models to study the pathophysiology of migraine and retinal dysfunction. By analyzing the consequences of individual mutations on channel function predictions about the neuronal dysfunction in the brain (FHM1) and retina (CSNB2) become possible and can be used to explain disease symptoms. This requires introduction of the mutations into the pore-forming subunits of the human channels using moelcular biological methods. Mutated channels are then expressed in suitable systems and functional changes of their opening and closing behaviour are analyzed using electrophysiological methods. Due to the absence of such a functional assay this kind of analysis has so far been impossible for CSNB2 mutations. Our group has recently succeeded in establishing a suitable functional assay. In the proposed research project the functional analysis of CSNB2 mutations will now be possible. In contrast to existing evidence suggesting that CSNB2 mutations completely prevent channel function we found in preliminary experiments that this is not true for all mutations. Therefore we can now test the interesting question about how and to which extent channel function must be altered to cause the clinical symptoms of CSNB2. Some mutations are located in regions which are known to contribute to the fine-tuning of channel function by intracellular calcium. An important aim of our studies will therefore also be to clarify the molecular determinants underlying this modulation. In addition to the opening and closing behaviour the expression density of the channels may be affected by the mutations which is expected to change cellular calcium influx during electrical activity. For FHM1 mutations this is already supported by functional evidence. In this proposal we also will apply a novel technique which allows the selective labeling of normal and mutant channel proteins to selectively detect them in the plasma membrane of neurons. Using this approach we can investigate the important question if mutations also change channel expression in the membrane and targeting to different neuronal compartments in cultured neurons. The results from our research project will provide important information about migraine pathophysiology and facilitate development of novel therapeutic concepts.

Familial Hemiplegic migraine type-1 (FHM1) and incomplete congenital night blindness (CSNB2) are human diseases resulting from mutations in different genes of voltage-gated calcium channels. Similar to targeted mutations in mice, these diseases represent unique models to study the pathophysiology of migraine and retinal dysfunction. By analyzing the consequences of individual mutations on channel function predictions about the neuronal dysfunction in the brain (FHM1) and retina (CSNB2) become possible and can be used to explain disease symptoms. This requires introduction of the mutations into the pore-forming subunits of the human channels using moelcular biological methods. Mutated channels are then expressed in suitable systems and functional changes of their opening and closing behaviour are analyzed using electrophysiological methods. Due to the absence of such a functional assay this kind of analysis has so far been impossible for CSNB2 mutations. Our group has recently succeeded in establishing a suitable functional assay. In the proposed research project the functional analysis of CSNB2 mutations will now be possible. In contrast to existing evidence suggesting that CSNB2 mutations completely prevent channel function we found in preliminary experiments that this is not true for all mutations. Therefore we can now test the interesting question about how and to which extent channel function must be altered to cause the clinical symptoms of CSNB2. Some mutations are located in regions which are known to contribute to the fine-tuning of channel function by intracellular calcium. An important aim of our studies will therefore also be to clarify the molecular determinants underlying this modulation. In addition to the opening and closing behaviour the expression density of the channels may be affected by the mutations which is expected to change cellular calcium influx during electrical activity. For FHM1 mutations this is already supported by functional evidence. In this proposal we also will apply a novel technique which allows the selective labeling of normal and mutant channel proteins to selectively detect them in the plasma membrane of neurons. Using this approach we can investigate the important question if mutations also change channel expression in the membrane and targeting to different neuronal compartments in cultured neurons. The results from our research project will provide important information about migraine pathophysiology and facilitate development of novel therapeutic concepts.