Improving hindlimb locomotor function by Non-invasive AAV-mediated manipulations of propriospinal neurons in mice with complete spinal cord injury

Abstract

After complete spinal cord injuries (SCI), spinal segments below the lesion maintain inter-segmental communication via the intraspinal propriospinal network. However, it is unknown whether selective manipulation of these circuits can restore locomotor function in the absence of brain-derived inputs. By taking advantage of the compromised blood-spinal cord barrier following SCI, we optimized a set of procedures in which AAV9 vectors administered via the tail vein efficiently transduce neurons in lesion-adjacent spinal segments after a thoracic crush injury in adult mice. With this method, we used chemogenetic actuators to alter the excitability of propriospinal neurons in the thoracic cord of the adult mice with a complete thoracic crush injury. We showed that activating these thoracic neurons enables consistent and significant hindlimb stepping improvement, whereas direct manipulations of the neurons in the lumbar spinal cord led to muscle spasms without meaningful locomotion. Strikingly, manipulating either excitatory or inhibitory propriospinal neurons in the thoracic levels leads to distinct behavioural outcomes, with preferential effects on standing or stepping, two key elements of the locomotor function. These results demonstrate a strategy of engaging thoracic propriospinal neurons to improve hindlimb function and provide insights into optimizing neuromodulation-based strategies for treating SCI.

An injury-induced serotonergic neuron subpopulation contributes to axon regrowth and function restoration after spinal cord injury in zebrafish

“…Spinal cord injury (SCI) causes locomotor dysfunction by severing the supraspinal connections as well as disrupting the neuronal network in spinal CPG 17 , 18 . Restoration of accurate locomotion requires reestablishment of neural circuits in spinal CPG 19 . The paucity of regrowth of injured axons in the adult mammalian central nervous system (CNS) is a major hurdle in understanding the intrinsic mechanisms that promote appropriate axon regrowth.…”

Improving functional recovery after severe spinal cord injury by a noninvasive dual functional approach of neuroprotection and neuromodulation

“…It is known that the BSCB is restored within 7 days post-SCI 9 , and this prevents macromolecular agent from penetrating in the late stage of SCI 39 . Fortunately, the restored BSCB still allows the penetration of small molecules or specific peptides or proteins 40 .…”

“…However, a hurdle to the application of these treatments [12][13][14][15] for CNS diseases such as SCI is that these agents cannot easily enter the CNS because of blood brain barrier (BBB) or brain spinal cord barrier (BSCB). In this regard, a recent study showed that BSCB disruption permits intravenously injected AAV9 to enter the injured spinal cord 9 . Although the underlying mechanism of injury-induced BSCB alterations remains unknown, this finding suggests the exciting possibility of designing relevant agents that can enter the spinal cord lesion.…”

“…Second, SCI triggers massive alterations in excitability, disrupting the overall balance of neural circuits in the injured spinal cord 6–8 . One demonstrated mechanism that underlies these changes is injury-induced downregulation of the expression of KCC2, a neuron-specific potassium chloride cotransporter, in neurons in injured spinal cord 6, 9 . Previous studies have reported that inhibition of inhibitory, but not excitatory, interneurons via genetic activation of KCC2 can increase overall excitability and transform initially dormant relay or endogenous spinal circuits into a functional state after SCI 6, 9 .…”

“…One demonstrated mechanism that underlies these changes is injury-induced downregulation of the expression of KCC2, a neuron-specific potassium chloride cotransporter, in neurons in injured spinal cord 6, 9 . Previous studies have reported that inhibition of inhibitory, but not excitatory, interneurons via genetic activation of KCC2 can increase overall excitability and transform initially dormant relay or endogenous spinal circuits into a functional state after SCI 6, 9 . However, it is yet not clear whether this strategy is efficacious in clinically translatable SCI models.…”