Noreen Bukhari
B.S. Georgetown University, 2004

4th Year Graduate Student

Advisor: Styliani-Anna Tsirka, Ph.D.

Department: Pharmacological Sciences

Graduate Program: Neuroscience


Abstract:

Noreen Bukhari¹, Stella Tsirka^2
1Program in Neuroscience, ²Department of Pharmacological Sciences Title:

Role of Tissue Plasminogen Activator in Axonal Regeneration of a Mouse Spinal Cord Injury Model

The National Spinal Cord Injury Database estimates that 11,000 new cases of spinal cord injury (SCI) occur in the United States each year with a prevalence of 253,000 persons. Acute administration of corticosteroids to suppress the body’s inflammatory response is the most widely used medical treatment for SCI. This treatment highlights two important points for researchers: the body’s secondary response is the more debilitating effect of the injury and new therapeutic approaches must focus on treating the chronic form of the injury. Chondroitinase ABC (ChABC) is a bacterial enzyme that has been shown to reduce the secondary damage and enhance axonal plasticity by degrading some of the inhibitory components of the glial scar. However, the exact mechanism underlying this repair remains unclear.

Our group has previously demonstrated that ChABC treatment enhances the interaction of the extracellular serine protease, tissue plasminogen activator (tPA) and its downstream target, plasmin, with the extracellular matrix molecules of the glial scar in in vitro and ex vivo models of SCI. We now directly test the contribution of this serine protease to ChABC-promoted axonal repair using mice deficient in tPA. Our central hypothesis is that tPA acts downstream of ChABC to promote axonal plasticity after SCI. We find that in SCI homogenates upregulation of tPA occurs at 4hours after a moderate contusion in WT mice and lasts for 14days, a time course that parallels CSPG upregulation. Western blot analyses of 14day SCI homogenates also indicate that in the absence of the tPA/Plg system, NG2, Neurocan, and Phosphacan degradation is reduced after ChABC treatment. Using an in vitro assay we test the role of tPA in ChABC mediated axonal plasticity. WT and tPA KO primary cortical neurons grown on ex vivo glial scars created zones of inhibition around extracellular CSPG molecules. We use this in vitro assay to measure the axon outgrowth induced by ChABC and its modulation by the tPA/plasminogen system. Our data, thus far, suggest that after SCI, the tPA/plg system may play an important role in ChABC-mediated regeneration. We aim to elucidate the mechanism of function of a promising therapy for SCI, and thereby help develop the good way to generate an environment permissive for regrowth of axons in the injured spinal cord.

Publications:
(pre-MSTP publications indicated with an *)

*Bacich DJ, Ramadan E, O’Keefe DS, Bukhari N, Wegozsewska I, Ojeifo O, Olszewski R, Wrenn CC, Bzdega T, Wroblewska B, Heston WD, Neale JH. Deletion of the glutamate carboxypeptidase II gene in mice reveals a second enzyme activity that hydrolyzes N-acetylaspartylglutamate. J Neurochem. 83(1): 20-9 (2002).

*Olszewski RT, Bukhari N, Zhou J, Kozikowski AP, Wroblewski JT, Shamimi-Noori S, Wroblewska B, Bzdega T, Vicini S, Barton FB, Neale JH. NAAG peptidase inhibition reduces locomotor activity and some stereotypes in the PCP model of schizophrenia via group II mGluR. J Neurochem. 89(4): 876-85 (2004).

Nolin W, Emmetsberger J, Bukhari N, Zhang Y, Levine J, Tsirka S. tPA-Mediated Generation of Plasmin is Catalyzed by the Proteoglycan NG2. GLIA. 56:177-189 (2008).