Enhancing KCC2 activity decreases hyperreflexia and spasticity after chronic SCI

Abstract

After spinal cord injury (SCI), the majority of individuals develop spasticity, a debilitating condition involving involuntary movements, co-contraction of antagonistic muscles, and hyperreflexia. By acting on GABAergic and Ca2+-dependent signaling, current anti-spastic medications lead to serious side effects, including a drastic decrease in motoneuronal excitability which impairs motor function and rehabilitation efforts. Exercise, in contrast, decreases spastic symptoms without decreasing motoneuron excitability. These functional improvements coincide with an increase in expression of the chloride co-transporter KCC2 in lumbar motoneurons. Thus, we hypothesized that spastic symptoms can be alleviated directly through restoration of chloride homeostasis and endogenous inhibition by increasing KCC2 activity. Here, we used the recently developed KCC2 enhancer, CLP257, to evaluate the effects of acutely increasing KCC2 extrusion capability on spastic symptoms after chronic SCI. Sprague Dawley rats received a spinal cord transection at T12 and were either bike-trained or remained sedentary for 5 weeks. Increasing KCC2 activity in the lumbar enlargement improved the rate-dependent depression of the H-reflex and reduced both phasic and tonic EMG responses to muscle stretch in sedentary animals after chronic SCI. Furthermore, the improvements due to this pharmacological treatment mirror those of exercise. Together, our results suggest that pharmacologically increasing KCC2 activity is a promising approach to decrease spastic symptoms in individuals with SCI. By acting to directly to restore endogenous inhibition, this strategy has potential to avoid severe side effects and improve the quality of life of affected individuals.Significance StatementSpasticity is a condition that develops after spinal cord injury (SCI) and causes major complications for individuals. We have previously reported that exercise attenuates spastic symptoms after SCI through an increase in expression of the chloride co-transporter KCC2, suggesting that restoring chloride homeostasis contributes to alleviating spasticity. However, the early implementation of rehabilitation programs in the clinic is often problematic due to co-morbidities. Here, we demonstrate that pharmacologically enhancing KCC2 activity after chronic SCI reduces multiple signs of spasticity, without the need for rehabilitation.

The role of KCC2 and NKCC1 in spinal cord injury: From physiology to pathology

“…Improvements in spasticity-like symptoms have also been reported (Boulenguez et al, 2010). When a KCC2 activator was administered to rats with spinal cord lesions, it was found that the expression of KCC2 was up-regulated in the membranes of motor neurons of the lumbar enlargement, and the spasticity symptoms were alleviated (Bilchak et al, 2021). Body Weight-Supported Treadmill training can also up-regulate KCC2 through the trkB pathway, regulating spinal cord excitability and reducing spasticity .…”

“…Then, activating downstream signaling pathways and regulating KCC2/NKCC1 expression, and effectively improve the spasticity and pain after SCI (Tashiro et al, 2015). And this effect can be inhibited by the BDNF blocker TrkB-IgG, suggesting that activation of BDNF is critical to relief from spasticity and pain symptom after SCI (Bilchak et al, 2021).…”

“…In brief, the downregulation of KCC2 expression below the injury site after SCI, especially in motor neuron membranes, can depolarize the intracellular membrane potential and exert excitatory effects, and may represent an important component in the occurrence of spasticity (Boulenguez et al, 2010;Bilchak et al, 2021). BDNF, exercise training, or regulation of neurotrophic factor levels can improve spasticity by promoting KCC2 expression (Tashiro et al, 2015;Ma et al, 2021;Talifu et al, 2022).…”