Armin Blesch - US grants

DESCRIPTION (provided by applicant): Delivery of neurotrophic factors by ex vivo gene therapy has been shown to induce axonal growth from different neuronal populations after spinal cord injury. While growth factor gene delivery is a potent means of promoting the growth of several axonal populations into spinal cord lesion sites, existing reports have not succeeded in promoting axonal growth beyond injury sites and into the distal, denervated spinal cord. For the translation of these studies into realistic treatments for spinal cord injury, improved techniques for neurotrophin delivery are needed to establish long distance axonal growth beyond the lesion site. Furthermore, the safety and tolerability of neurotrophin gene delivery must be tested. This project will investigate regulatable expression systems for ex vivo and in vivo gene delivery of neurotrophic factors to promote anatomical axonal growth beyond spinal cord lesion sites, and potential functional recovery. Previous studies from the laboratory of the Principal Investigator and others have shown that the cellular delivery of neurotrophic factors to sites of spinal cord injury elicits extensive axonal growth but this growth is either restricted to the immediate injury site or for short distances beyond it. In the proposed experiments, we will sequentially turn on and off gene expression at various sites and times after spinal cord injury to determine whether extensive axonal growth beyond injury sites and to denervated distal segments can be achieved. The ability to regulate growth factor expression in vivo will also markedly enhance the safety of gene therapy for therapeutic applications. Adverse effects of neurotrophic factors could include hyperalgesia and pain. We will therefore investigate whether neurotrophin delivery to the injured spinal cord induces thermal and mechanical hyperalgesia, and if the regulation of neurotrophin expression can prevent or reverse this development. If successful, these studies will establish practical strategies for optimizing growth factor delivery to sites of spinal cord injury and can be extended to chronic models of spinal cord injury and larger animal studies in the future. Further, this could lead to the development of therapies for clinical translation.

[unreadable] DESCRIPTION (provided by applicant): Delivery of neurotrophic factors to sites of spinal cord injury (SCI) has been shown to induce axonal growth from different neuronal populations. While cellular growth factor gene delivery is a potent means of promoting the growth of several axonal populations into spinal cord lesion sites, novel strategies need to be developed to increase the distance of axonal growth and to define the conditions needed to direct axonal growth across a lesion site. In studies supported by an R21 grant we have determined that in vivo neurotrophin gene transfer beyond a spinal cord lesion site establishes gradients of neurotrophic factors and can thereby direct axons across a spinal cord lesion site. The mechanisms underlying morphological and functional outcomes and the conditions needed to achieve persistent morphological and functional improvements will be studied in this proposal. We will investigate the hypothesis that transient, regulated gradients of the neurotrophin BDNF will be sufficient to induce axonal bridging across a spinal cord lesion site, morphological plasticity and reinnervation, resulting in persistent functional recovery. BDNF gradients across a cervical spinal cord lesion site filled with bone marrow stromal cells will be established using in vivo lentiviral gene transfer. Mechanisms of morphological and functional outcomes will be investigated in detail in well-defined transection models of SCI that allow the discrimination between sprouting of spared projections and true regeneration of injured axons. Anterograde and retrograde tracing and specific re-transections will allow the identification of different mechanisms that could contribute to reinnervation and functional recovery. Using tetracycline-regulated, lentiviral BDNF gene transfer we will define the conditions needed to retain the connectivity and function of regenerated axons and we will determine whether a practical need for extended gene expression exists for the formation and maintenance of newly formed synapses. If successful, these studies will establish practical strategies for growth factor delivery to the injured spinal cord that can lead to the development of novel therapies for spinal cord injury. [unreadable] [unreadable] [unreadable] [unreadable]

Abstract In addition to impairment of motor, autonomic and sensory function, severe pain is highly prevalent in patients after spinal cord injury. This project aims to better understand the cortical mechanisms and changes underlying the development of central neuropathic pain after spinal cord injury challenging the assumption that hyperexcitability of neuronal circuits can only be modified by directly blocking excitation or increasing the activity of inhibitory circuits. Our previous work has characterized the onset and maintenance of chronic central neuropathic pain in a mouse model of contusion injury. Our preliminary data also show that sensory cortical activity is initially decreased after a transient spinal cord ischemia followed by hyperactivity paralleling the onset of pain behavior. This hyperactivity and the associated pain behavior can be diminished by optogenetic stimulation of somatosensory cortex early after injury. In addition, we have shown that treadmill training can prevent the development and partially reverse pain-associated behavior in mice. We now aim to characterize in detail changes in somatosensory cortical activity after traumatic spinal cord injury in mice using patch- clamping and in vivo calcium imaging in transgenic mice. We also aim to determine whether modulating cortical activity by somatosensory training can modulate cortical hyperactivity after spinal cord injury and thereby ameliorate neuropathic pain. Thereby, we will advance our understanding of the development and maintenance of chronic pain after spinal cord injury, identify cortical mechanisms underlying the development of chronic pain that can be translated into novel pharmacological and rehabilitative treatments that interfere with homeostatic plasticity for a comprehensive pain management.