Our lab has several projects in progress simultaneously. Each lab member typically takes the lead on one project, but all projects are discussed at weekly lab meetings. All projects use classical molecular biology techniques such as RT-PCR, western blotting, in situ hybridization, immunohistochemistry, electron microscopy, and tissue culture; many projects also involve clinical techniques such as electrophysiology. The mixture of clinical and basic science approaches aims to correlate molecular etiologies with clinical applicability.

 

Projects

The Role of Neural Wound Healing in the pathogenesis of Chronic Nerve Compression to explain why Surgery may not be enough

Chronic nerve compression (CNC) injuries such as carpal tunnel syndrome cause patients significant morbidity with the ensuing loss of sensation and motor function. Recent advancements have prompted a reinterpretation of compressive neuropathies as possibly an example of a wound healing model consisting of inflammation, angiogenesis, cellular proliferation, and connective tissue remodeling. Previous studies have demonstrated the prevalence of tissue inflammation, increased neural vasculature, and Schwann cell proliferation during the progression of CNC injury. Because little is known about the ECM composition in human neuropathies, their potential role to favor or impede nerve repair in human disorders remains largely unexplained. We proposed that the extracellular matrix of peripheral nerves undergoes extensive modification following CNC injury and may emulate biologic processes similar to classic wound healing. Our preliminary results demonstrate CNC injury induces a progressive and significant increase in ECM components such as fibronectin, laminin, and collagen type IV at the level of mRNA transcription and protein translation. Furthermore, we were able to localize their up-regulation to the site of CNC injury compared to control mice supporting the hypothesis that CNC injury does induce ECM remodeling. In contradistinction to chronic constriction injury, CNC injury also does not up-regulate TNF-alpha at the site of compression. By considering the pattern of ECM expression with our quantitative and qualitative findings in two different animal models for CNC injury, there is a sequence of events involved in the connective tissue remodeling process that appears to be neural wound healing. CNC injury seems to stimulate a biologic response that mimics canonical wound healing and leads to up-regulation of ECM components, such as laminin, collagen, and fibronectin, with eventual scar formation. This pathway favors tissue repair by structural support and restricts the capacity for functional tissue and nerve regeneration after remodeling takes place.

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Desert Hedgehog has a Neuroprotective Effect Against Mechanical Stimuli

Defining the molecular mechanisms underlying chronic compressive neuropathies (CNC) is crucial for identifying novel treatment methods. Desert hedgehog (dhh) is a Schwann cell produced protein responsible for formation of nerve perineurium. We hypothesize that it is a potential therapeutic target, given its interaction with extracellular matrix and connective tissue. Desert hedgehog deficiency appears to accentuate peripheral nerve demyelination in chronic compression neuropathies, signifying a vital role for dhh in the propagation of nerve impulses.

 

MMP-3 Inhibition Preserves the Motor Endplate after Traumatic Nerve Injury

Traumatic Peripheral Nerve Injuries often produce significant functional deficits despite optimal medical management. Denervation likely alters the environment that sustains the motor end plate, leading to end-organ atrophy of the neuromuscular junction(NMJ). Assembly and maintenance of the NMJ depends highly on interaction between agrin and muscle-specific kinase(MuSK). Agrin, in turn, is degraded by Schwann cell-derived matrix metalloproteinase 3(MMP-3). The current study focuses on assessing the NMJ after long-term denervation in both wildtype and MMP-3 null mice and investigates whether the NMJ may be stabilized by agrin overexpression secondary to knockout of MMP-3. To date, there is not study that has rigorously investigated the role of agrin in the maintenance of the NMJ following long-term denervation injury. Given the evidence that agrin is closely linked to the integrity of the NMJ, the present study aims to determine whether the stability of the post-synaptic apparatus after prolonged denervation is improved in MMP-e null mice in contrast to the wildtype phenotype.

Our preliminary results show that wildtype muscle following denervation demonstrated significant attenuation in acetylcholine receptor area as well as a pattern of conversion to an immature receptor phenotype, particularly at later time points. Surprisingly, receptors in MMP-3 knockout muscles showed less decrease in area from baseline. In addition, agrin and MUSK immunoreactivity remained at acetylcholine receptors late after denervation injury in MMP-3 null mice whereas expression for these proteins progressively disappeared in the wildtype animals. Western blot data revealed an increase in expression in agrin in both animal groups after injury but also a larger decrease in MuSK phosphorylation in wildtype mice.

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For the second time in three years, the Orthopaedic Research & Education Foundation (OREF) has chosen one of UC Irvine Orthopaedic residents to receive their prestigious OREF Resident Clinician Scientist Training Grant. The 2014 recipient of this award is Dr. Minal Tapadia.

 

Dr. Ranjan Gupta has been selected as an ABC Traveling Fellow, one of the most prestigious orthopaedic awards and honors.

 

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