Alexander Rabchevsky, PhD - US grants

DESCRIPTION (provided by applicant): Autonomic dysreflexia is a potentially life-threatening complication of spinal cord injury (SCI) that is characterized by episodic hypertension (high blood pressure) due to sudden, massive discharge of the sympathetic neurons in the injured spinal cord. The sympathetic neurons enable the 'fight or flight' response of an individual (e.g. more blood flow to the muscles). The reason the sympathetic neurons are so sensitive is that descending inhibitory pathways from higher brain centers are interrupted as a result of the SCI. In spinal injured patients, autonomic dysreflexia is frequently triggered by distension of, or activity within pelvic viscera (bladder or bowel). Therefore, distension of the bladder or bowel sends a signal via sensory neurons to the sacral spinal cord (the lower back). From here, the signal is relayed to thoracic and lumbar sympathetic neurons (chest region of the cord) by relay neurons. Because there is no modulating influence from the higher brain, the action of the sympathetic neurons is unopposed. As a result, the sudden increase in their activity following visceral stimulation causes a sudden rise in blood pressure (up to 200 mmHg) that can cause potentially fatal brain or spinal hemorrhage, seizures, as well as severe headache, shivering, sweating and anxiety. Unfortunately, little is known about the anatomical or functional relationships between the visceral sensory neurons, the spinal relay neurons, and the sympathetic neurons. We propose to use a variety of histological and physiological techniques in a well-defined rat model of autonomic dysreflexia to discover the anatomical connections between these three types of neurons that are critical for the development of autonomic dysreflexia. It is currently not known how visceral sensory information entering the lumbosacral spinal cord is relayed to sympathetic preganglionic neurons in the intermediolateral cell column (IML) of the thoracolumbar cord. Since nociceptive afferent sprouting after SCI is NGF-dependent and is correlated with the incidence of autonomic dysreflexia, we have injected temperature sensitive adenoviruses (Adts) encoding nerve growth factor (NGFAdts) into thoracic, lumbar and sacral spinal cord to trigger sprouting to determine which regions are critical for eliciting autonomic dysreflexia. Overexpression of NGFAdts only in the T13/L1 and L6/S 1 segments produced significant increases in arterial blood pressure evoked by colorectal distension versus injured controls injected with GFPAdts. This suggests that following spinal transection, pelvic visceral information is relayed from its input site in the lumbosacral dorsal horn to the IML via unidentified projection pathways. This proposal has 4 goals. Firstly, we will use anterograde tracing of biotinylated dextran amine (BDA) from the L6/S 1 cord, and retrograde transsynaptic tracing of pseudorabies virus (PRV) from sympathetic pre-vertebral ganglia to identify the neural pathways that transmit visceral information from lumbosacral to thoracic cord after SCI. Secondly, since NGFAdts exacerbate dysreflexia, we will establish whether this correlates with increased pathway sprouting. Thirdly, since it is possible that NGF-independent afferents play a role in autonomic dysreflexia, we will inject Adts encoding other growth factors, FGF-2, NT-3, BDNF and GDNF, into multiple levels of the lumbosacral cord. We will also assess their direct influence on lumbar propriospinal neurons by injecting them in the distal thoracic cord. Finally, based on our recent evidence, we will inject chemorepulsive semaphorin3aAdts after injury into the lumbosacral spinal cord in an attempt to thwart early sprouting events and minimize dysreflexia, as well as establish whether chronic injections are capable of inducing retraction of established sprouts. This information will form the basis for developing potential treatments for this common and debilitating complication of SCI.

DESCRIPTION (provided by applicant): Spinal cord injury (SCI) is a long-term health care problem in the United States, and with the exception of the modestly effective methylprednisolone, there is currently no neuroprotective intervention clinically available for treatment of acute SCI. Our published data and preliminary results demonstrate that oxidative damage to key mitochondrial enzymes and subsequent mitochondrial dysfunction is key to the neuropathological sequalae following SCI. This proposal focuses on directly targeting mitochondrial dysfunction as a novel therapeutic intervention for contusion SCI, the fundamental concept being that SCI-induced excitotoxicity increases mitochondrial Ca2+ cycling/overload and the production of reactive oxygen species (ROS), ultimately leading to mitochondrial dysfunction and glutathione (GSH) depletion. Our approach is two-pronged, aimed at reducing mitochondrial ROS production utilizing a novel, cell-permeant antioxidant and GSH precursor, NACA (the amide form of N-acetylcysteine), as well as an alternative biofuel substrate for energy production, acetyl-l-carnitine (ALC), following SCI. Our published and preliminary data signify that both NACA and ALC improve mitochondrial bioenergetics following contusion SCI in rats, and that prolonged NACA or ALC treatment increases tissue sparing following injury. The planned experiments are designed to test the novel hypothesis that reducing oxidative damage to key mitochondrial proteins will maintain mitochondrial bioenergetics, thus leading to increased neuroprotection and improved functional recovery following contusion SCI. Specifically we will: 1) Characterize oxidative damage to specific mitochondrial proteins involved in bioenergetics and test the hypothesis that NACA treatment ameliorates mitochondrial oxidative damage following SCI, 2) Test the hypothesis that a combinatorial treatment with NACA and ALC will act synergistically to preserve mitochondrial homeostasis following SCI, and 3) Test the hypothesis that a combinatorial treatment with NACA and ALC will increase tissue sparing and promote long-term functional recovery following SCI. Critically, this application is built around the utilization of several novel techniques we have developed for isolating synaptic (neuronal) and non-synaptic (soma and glia) mitochondria from the injured spinal cord, as well as an L1/L2 contusion SCI paradigm that demonstrates a significant correlation between neuroprotection and remarkable improvements in recovery of hind limb function. Collectively, the proposed experiments will pinpoint key mitochondrial events that could be potential novel targets for pharmacological interventions to more effectively treat SCI and, perhaps, other CNS injuries. PUBLIC HEALTH RELEVANCE: Spinal cord injury (SCI) is a serious health care problem in the United States. However, with the exception of the modestly effective methylprednisolone, no neuroprotective intervention is clinically available for treatment of acute SCI. This proposal focuses on directly targeting mitochondrial dysfunction as a novel therapeutic intervention following spinal cord injury (SCI).

? DESCRIPTION (provided by applicant): The current proposal is designed to develop of a new research area that is aimed at transplanting mitochondria into the injured rodent spinal cord as a therapeutic strategy following traumatic spinal cord injury (SCI). We and others have found that maintaining normal mitochondrial bioenergetics after contusion SCI fosters both neuroprotection and functional recovery. However, no studies have examined the effects of transplanting exogenous mitochondria into spinal cord tissue after injury in an attempt to normalize overall cellular bioenergetics and spare adjacent host tissues. Accordingly, this new line of investigations will test, ultimately, whether transplanting exogenous healthy mitochondria into the injured spinal cord promotes functional neuroprotection. Using a rat model of contusion SCI, we have preliminary data showing that allogeneic transgenically-labeled (turboGFP) mitochondria derived from PC12 cells microinjected around the injury site maintain overall cellular bioenergetics assessed 24 hrs later. Moreover, using confocal microscopy to evaluate specific antibodies to both inner and outer mitochondrial membranes, we have preliminary evidence that grafted turboGFP mitochondria integrate within naïve and injured spinal cord tissues. Based on these seminal findings, we propose to conduct a series of transplantation strategies to deliver mitochondria around the injury sites. The ultimate goal is to identify a potential autologous cell source of mitochondria (i.e., leg muscle) to prevent secondary tissue injury that is mediated, in large part, by mitochondrial loss and dysfunction. In summary, Aim 1a will comparatively employ a dose-response approach to assess whether transplanted MitoTracker Red-labeled mitochondria isolated from muscles are equally effective as allogeneic turboGFP mitochondria on cellular bioenergetics and the extent of inflammation following acute contusion SCI. Aim 1b will then assess comparatively the frequency and distribution of labeled mitochondria incorporated into host cells over the first week post-injury. Finally, Aim 2 will establish whether transplantation of muscle-derived mitochondria increases long-term tissue sparing and recovery of hindlimb locomotion following SCI. This project has translational potential wherein mitochondria, notably autologous, can be transplanted around the injury site to spare penumbral tissues. Based on the collective expertise of the PI in cellular transplantation into injured spinal cord tissue and both Co-Is in bioenergetic assessments and mitochondrial-targeted therapeutics for neurotrauma, along with our preliminary feasibility data, there are no foreseen technical obstacles to successfully carry out this project. Notably, future experiments stemming from the results of the current proposal will be designed to test delayed grafting paradigms to extend a more clinically relevant therapeutic time window for transplantation of mitochondria to promote functional recovery in more chronic SCI models.

Project Summary Spinal cord injury (SCI) affects approximately 300,000 Americans resulting in devastating neurological and physical limitations. SCI in the chronic phase is complicated by muscle spasms, which are to a large degree caused by hyperactivation of the serotonin receptor 2C (5HT2C) caudal to the injury. Through a combination of alternative splicing and editing, the G-protein coupled receptor generates at least 25 isoforms with different regulatory properties: one intracellular truncated receptor 5HT2C_tr, one non-edited full-length receptor 5HT2C_Fl_INI and 23 full length edited receptors 5HT2C_FL_ed. The ratio of these isoforms wherein the 5HT2C_FL shows constitutive activity plays a major part in the maladaptation after injury. SCI leads to a loss of editing activity of ADAR2 (adenosine deaminase acting on RNA), which results in a downregulation of 5HT2C_FL_ed isoforms, relative to the 5HT2C_FL_INI. Extending our joint published work (Zhang et al., 2016, EMBO Mol. Med)1, we concentrated on the novel 5HT2C_tr isoform that sequesters the 5HT2C_FL intracellularly. We found an increase of the 5HT2C_tr isoform after SCI, possibly as an adaptation to prevent the constitutively active 5HT2C_FL_INI from hyperactivity. To intervene with the isoform ratios, we developed a series of oligonucleotides that either increase or decrease the 5HT2C_tr /5HT2C_FL_INI ratio, as well as an antiserum that is specific for the 5HT2C_tr protein. Using these tools, we will test the hypothesis that SCI leads to an increase in both constitutively active 5HT2C_FL_INI and its downregulating 5HT2C_tr isoform. This change deregulates spinal cord neuronal activity leading to spasms, likely due to insufficient 5HT2C_tr isoform to stop the 5HT2C_FL_INI activity. We will thus further test whether these spasms can be mitigated using our developed oligonucleotides that promote 5HT2C_tr. Using an established S2 spinal cord transection rat model, we will map the spatial and temporal changes in receptor isoforms and test the influence of splicing-changing oligonucleotides on the development of tail spasms. The oligonucleotides interfere with the serotonin system by changing the surface localization of constitutive active 5HT2C_FL, which is a novel approach compared to ligand- based drugs activating surface receptors. Using this innovative approach targeting the pre-mRNA, these studies are significant with great potential to treat spasticity, which is a major co-morbidity of SCI.

Project Summary/Abstract Mitochondrial dysfunction is pivotal to the neuropathological sequelae following traumatic spinal cord injury (SCI). During this initial time window, there is a significant loss of mitochondria with an inflammatory/oxidative environment that perpetuates the pathophysiology. It is hypothesized that to rescue the cellular damage occurring following SCI, one must replace damaged mitochondria, while also changing the damaging microenvironment. We have documented that maintaining endogenous mitochondrial bioenergetics with acetyl-l-carnitine (ALC), an alternative mitochondrial biofuel, or reducing oxidative stress by replenishing endogenous antioxidant, glutathione (GSH) with N-acetylcysteine amide (NACA) after SCI results in increased, but limited long-term functional neuroprotection. We have also reported that acute mitochondrial transplantation (MitoTxp) using intraspinal injections of mitochondria isolated from rat soleus muscle significantly preserved bioenergetic function 48hr post-SCI. However, this was sporadically successful due to the challenges of both accumulating mitochondria at the site of injury and maintaining their viability prior to cellular uptake. In the current proposal, we will develop a thermo-gelling, erodible hydrogel system for the localized delivery of viable mitochondria to test the neuroprotective efficacy of combined MitoTxp and pharmaceutical interventions (ALC and/or NACA) after contusion SCI. The use of an injectable hydrogel will permit the development of a local environment which can aide in maintaining mitochondrial health through optimization of the hydrogel niche. We will determine 1) optimum constituents for isolated mitochondria to remain viable for extended periods in polymeric hydrogels, 2) whether exogenous mitochondria transplanted via less invasive intrathecal route equally preserve integrity of bioenergetics compared to intraspinal route and 3) consequences of acute or delayed MitoTxp in combination with ALC and/or NACA on bioenergetics, oxidative stress, and functional neuroprotection after SCI.