Carbonic anhydrase I (CA1) is the cytosolic isoform of mammalian α-CA family members which are responsible for maintaining pH homeostasis in the physiology and pathology of organisms. A subset of CA isoforms are known to be expressed and function in the central nervous system (CNS). CA1 has not been extensively characterized in the CNS. In this study, we demonstrate that CA1 is expressed in the motor neurons in human spinal cord. Unexpectedly, a subpopulation of CA1 appears to be associated with endoplasmic reticulum (ER) membranes. In addition, the membrane-associated CA1s are preferentially upregulated in amyotrophic lateral sclerosis (ALS) and exhibit altered distribution in motor neurons. Furthermore, long-term expression of CA1 in mammalian cells activates apoptosis. Our results suggest a previously unknown role for CA1 function in the CNS and its potential involvement in motor neuron degeneration in ALS.

Background: Drosophila models of amyotrophic lateral sclerosis (ALS) have been widely used in understanding molecular mechanisms of ALS pathogenesis as well as discovering potential targets for therapeutic drugs. Mutations in the copper/zinc superoxide dismutase (SOD1) cause ALS by gain of toxic functions and induce toxicity in fl y motor neurons. Results: In this study, we have determined that human carbonic anhydrase I (CA1) can alleviate mutant SOD1-induced motor neuron toxicity in the transgenic fl y model of ALS. Interestingly, we found that motor neuron expression of CA1 could independently induce locomotion defect as well as decreasing the survival rate. In addition, CA1-induced toxicity in motor neurons is anhydrase activity-dependent. Mechanistically, we identifi ed that both SOD1-and CA1-induced toxicity involve the activation of eIF2 in the ER stress response pathway. Downstream activation of the JNK pathway has also been implicated in the induced toxicity. Conclusion: Our results have confi rmed that SOD1-induced toxicity in fl y motor neuron also involves endoplasmic reticulum (ER) stress pathway. More importantly, we have discovered a new cellular role that CA1 plays by antagonizing mutant SOD1-induced toxicity in motor neurons involving the ER stress pathway. Such information can be potentially useful for further understanding disease mechanisms and developing therapeutic targets for ALS. Carbonic Anhydrase I modifi es SOD1-induced motor neuron toxicity in Drosophila via ER stress pathway