Inability of lesioned axons in the adult mammalian central nervous system (CMS) to regenerate has been hypothesized to result from both a decrease in intrinsic regenerative capacity of mature neurons and a local inhibitory environment at the site of injury. It appears that the majority of inhibitory activities in the adult CNS are derived from two CNS-specific glial cell types, the oligodendrocyte and astrocyte. While chondroitin sulfate proteoglycans (CSPGs) have been implicated as a major class of inhibitors in astrocyte-derived glial scar, several myelin-associated molecules account for the major inhibitory activities of the oligodendrocytes. Our recent data demonstrated that conventional isoforms of protein kinase C (PKC) are key signaling components in the pathways that mediate the inhibitory activities of both myelin components and CSPGs. Strikingly, intrathecal infusion of a PKC inhibitor, Go6976, into the site of C3 dorsal hemisection, made by a unique VibraknifeTM device, promoted robust axonal regeneration of the ascending dorsal column (DC) across and beyond the lesion site which led to functional reinnervation. Our data also indicates that PKC inhibition may have an effect on regeneration of the rubrospinal tract (RST). It remains unclear, however, whether these regenerating axons are able to reach their original targets and form synaptic connections. Unexpectedly, the same PKC inhibitor did not promote the regeneration of the corticospinal tract (CST) in this model. These results provide us with a unique opportunity to investigate whether different CNS pathways differ in their requirements for regeneration and how regenerating axons behave in the injured adult CNS. In this application, we will explore the role and mechanism of PKC inhibition-mediated axonal regeneration and functional recovery after the C3 dorsal hemisection with the following three (3) Specific Aims:
Aim 1 will determine anatomical regeneration, reinnervation, somatotopic organization and function following DC axonal regeneration elicited by PKC inhibition.
Aim 2 will determine whether PKC inhibition also induces regeneration of another descending pathway, the RST, in the same lesion model to test whether it has a broad effect on axonal regeneration.
Aim 3 will explore combinatorial strategies to maximize regeneration and functional recovery after C3 dorsal hemisection. Specifically, we will combine the PKC inhibition with three promising strategies to: 1) enhance injured neuron's intrinsic regenerative capacity, 2) provide chemotropism for regenerating axons with neurotrophins, and 3) remove CSPGs deposited within the glial scar. We will examine whether the combination strategies will result in stronger neurite outgrowth on inhibitory substrates in vitro and greater axonal regeneration and functional recovery in vivo. Collectively, these studies may allow us to understand mechanisms underlying PKC-mediated axonal inhibition of different CNS pathways and provide new insights into designing effective therapeutic strategies to encourage axonal regeneration of different types of axons in the injured adult spinal cord.
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