Background : Plasmin, a versatile and aggressive master enzyme, is ubiquitously distributed in its zymogen form, plasminogen, to extracellular matrix, cell and microbial surfaces ,as well as the blood .The predominant plasminogen, activator present in both the vascular and nervous systems is tissue plasminogen activator (t-PA).Once activated ,plasmin has broad substrate specificity and plays important roles in activating multiple latent proteases, cytokines and factors involved in cell invasion, chemotaxis, fibrinolysis and tissue remodeling during many pathophysiological processes . This laboratory has established that t-PA is synthesized, transported and released in its free active form by sympathetic neurons that innervate blood vessel walls and other tissues. Previously ,vascular endothelial cells were thought to be the primary source of t-PA that is released into the circulation ,while sympathetic neurons were thought to release norephinephrine and neuropeptides into vessel walls .The distribution of a potent serine protease by sympathetic fibers has altered this view and points to a new intersection of neurologic, vascular, immunologic and matrix sciences. This is based on evidence that plasmin production and its effects in innervated tissues throughout the body are autonomically controlled, and therefore subject to the multiple effects of stress, aging, immune and other forces. An example of this in neuroimmunology is the fact that systemic immunoregulatory proceses mediated by T cells are aborted by chemical sympathectomy. An intriguing feature of the sympathetic distribution of t-PA is the heterogeneity of innervation density among various organs and tissues, an indicator of intensity of local plasmin proteolysis. For instance, the high density of the sympathetic axon plexus in small precapillary resistance arteries and arterioles compared to larger vessels. .Since these vessels number over ten million ,and control both systemic blood pressure and downstream capillary perfusion the concentration of plasmin production at this site may be essential for physiologic regulation of these functions, and play a role in vascular disease pathogenesis.

Current Studies: Small arteries and arterioles display a much broader presence of immunostained t-PA in the sub-adventitial sympathetic nerve plexus than the endothelium. But while endothelium is known to extend throughout the organism, a comparable systemic network of t-PA -bearing sympathetic fibers able to regulate plasmin production in vessel walls and tissue spaces has not yet been clearly visualized. To strengthen the morphologic evidence for such a system we have created a new transgenic mouse model in which fine t-PA-bearing nerve fibers embedded in tissues are specifically targeted by a t-PA transgene linked to a green fluorescent protein. Confocal and ultrastructural images visualize the confinement of t-PA expression to vessel walls, bone marrow, periostium, eye and other tissue matrices. T-PA release assays from these tissues are correlated to innervation density to establish a structure /function basis for this new neural plasminogenic system .In related studies, the effects of ageing and stress on t-PA/plasmin production by the sympathetic nervous system are examined. Collaborative studies of neural t-PA effects on immunoregulation are done with Dr Cone's laboratory .An additional need is to establish that t-PA released from sympathetic nerve endings in the outer wall of innervated microvessels passes through thin walls and enters the microcirculation. This is thought to happen during sympathetic/adrenergic stimulations but has not been visualized. Meta-confocal imaging of serum for release of the GFP/t-PA and photofluorometric emission curve analysis

are done to verify release into the circulation. Studies on the role of neural t-PA release in chronic disease and knock- out models - eg diabetes, hypertension, osteoporosis and malignancy will follow.

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