Periodic Reporting for period 4 - HOW2WALKAGAIN (Mechanisms of recovery after severe spinal cord injury)
Periodo di rendicontazione: 2021-01-01 al 2021-06-30
The objective of HOW2WALKAGAIN was to leverage the most advanced neurotechnologies to identify the neural mechanisms underlying the recovery of walking during electrical spinal cord stimulation. Our ultimate goal was to exploit this fundamental knowledge to translate this therapy in humans.
During this project, we found that electrical spinal cord stimulation modulates specific neuronal subpopulations in the spinal cord through the recruitment of afferent fibers innervating sensory receptors embedded into muscles, called proprioceptors. This understanding allowed us to develop more advanced stimulation protocols that exploit the anatomical organization of the proprioceptive system to mediate a more robust facilitation of leg movements. Translation of these protocols in clinical settings allowed nine individuals with chronic SCI to regain the ability to walk. Moreover, neurorehabilitation enabled many individuals to regain voluntary control over the activity of previously paralyzed muscles, even when the stimulation was turned off. This neurological recovery had not been observed with conventional stimulation protocols. Consequently, we modelled all the features observed in humans in rodent models in order to identify the mechanisms underlying this unexpected recovery. We thus deployed whole-nervous system imaging, single-cell technologies, and cell-specific interrogations in transgenic mice to catalogue the molecular choreography of recovery from spinal cord damage during neurorehabilitation supported by electrical spinal cord stimulation. We discovered that this therapy promotes the directed growth of neural projections from specific brain regions onto specific neuronal subpopulations in the spinal cord that become essential to walk after paralysis.
This understanding also allowed us to target other neurological functions that are impacted by SCI. For example, many individuals with severe SCI showed abnormally low levels of blood pressure, called orthostatic hypotension, that escalate risks of cardiovascular diseases and dramatically impact the quality of life. We found that we could use the same principles to modulate the sympathetic circuits that regulate blood pressure. This understanding supported the development of a spinal cord neuroprosthesis that precisely regulates blood pressure in real-time.
Our ERC proof-of-concept is enabling the translation of these scientific advances into tailored clinical devices for the recovery of mobility and hemodynamic stability. To accelerate this translation, we founded the start-up ONWARD Medical, which aims to bring this therapy to the market. Our ultimate goal is to bring these clinical innovations to the community of people with SCI.
We also implemented an advanced pipeline to characterize the anatomical and functional organization of projection circuits across the entire brain. This pipeline combines virus-mediated tract tracing, whole brain-spinal cord tissue clearing, activity-dependent labeling of neurons, 3D light-sheet microscopy, cell registration in Allen Institute anatomical atlas, and functional connectome analysis. This unbiased analysis is uncovering specific networks of circuits involved in the recovery of leg movements after SCI, thus opening the possibility to target these circuits to further enhance functional recovery.
Moreover, we are conducting single-nucleus sequencing analysis to identify transcriptomic changes of neurons and supporting cells in the spinal cord that underlie improvement of function in response to rehabilitation. This analysis is identifying neurons with unique molecular profiles that are involved in the production of locomotion after rehabilitation and could become new targets to further improve recovery. These results also informed the design of regeneration therapies that allowed us to promote the regrowth of nerve fibers across and beyond a complete SCI.
These combined methodologies and studies are thus yielding scientific results that are modifying our understanding of the recovery mechanisms after SCI, and how electrical spinal cord stimulation and intensive rehabilitation training are improving functional recovery. Many results have been disseminated in high profile journals and in clinical trials.