Chemogenetic Neuromodulation of Cervical Spinal Interneurons: A Novel Preclinical Translation Strategy to Restore Breathing After Chronic Cervical Spinal Cord Injury

Introduction: Cervical spinal cord injury (cSCI) disrupts descending drive to the spinal respiratory circuitry resulting in significant respiratory compromise. Dysfunctional breathing is a significant cause of morbidity and mortality after cSCI despite mechanical ventilation. The ability to restore breathing in the chronic phase after cSCI is an overwhelming yet essential goal. Our previous work demonstrated that a small population of cervical spinal excitatory interneurons (eINs) can be stimulated to produce acute increases in respiratory motor output. However, it is unknown if this strategy can be translated into a non-transgenic preclinical model to improve breathing in the late chronic phase of cSCI.

Methods: Using AAV technology, we expressed designer receptors exclusively activated by designer drug (DREADD) selectively in cervical eINs four weeks after C2 level spinal cord hemisection (C2Hx). Two weeks after viral injections, cervical eINs were stimulated via subcutaneous injection of CNO, the DREADD ligand. The effect of CNO-mediated activation of cervical eINs on diaphragmatic motor function was assessed via electromyography. The overall effect of this approach on the ability to respond to acute respiratory challenges (hypercapnia and hypoxia) were assessed using whole-body plethysmography.

Results: Chemogenetic stimulation of cervical eINs after chronic cSCI led to significant improvement in ventilation. Importantly, these results demonstrate the feasibility of how the DREADD system can now be implemented to target the spinal eINs under the CAMKIIa promotor in wild type mice demonstrating the translational capacity of this strategy.

Conclusion : This promising therapeutic strategy for improving respiratory function after SCI in a clinically relevant model cSCI. This is a critical step to determining the future translation of this chemogenetic approach in persons with chronic cSCI. AAVs tested in this study are particularly promising for clinical translation because of their safety profile, and the FDA has already approved many AAV-based therapeutics.