UC San Diego

Schwann cells play a vital role in maintaining homeostasis of the nerve and in recovery when an injury occurs in the peripheral nervous system. An improperly healed nerve or impaired Schwann cells can lead to the development of neuropathic pain. Most treatments for neuropathic pain treat the symptom but not the underlying cause. By developing drugs that can activate Schwann cells to become a recovery phenotype can be a method of treating neuropathic pain. The binding of the hemopexin domain of MMP9 to the LRP1 receptor of Schwann cells was previously found to cause the same signaling pathways that can activate these cells to differentiate into a recovery phenotype. Thus, developing small peptides of MMP9 to bind to LRP1 and cause the same signaling response, would be a viable option for developing a treatment for neuropathic pain.

Using the crystal structure of MMP9 hemopexin domain as a template, 4 peptides were designed from the hydrophilic regions of the protein. These peptides were subjected to in vitro cell signaling studies, in situ pull downs assays and in vivo nerve crush assays to assess their biological similarity and relevance compared to the parent MMP9 hemopexin domain. Of the 4 peptides, peptide 2 with the sequence “SGRGKMLLFSGRRLWRFDVKAQ,” was seen to have similar activity to the parent MMP9 hemopexin domain.

To observe if the peptide would be capable of alleviating neuropathic pain, a drug delivery system needed to be developed to locally delivery the peptide to a PNL rat model. Alginate hydrogels were first used with a PNL injury model and seen to have no behavioral changes. However, due to high levels of inflammation seen in the immunohistochemistry and immunoblots, a PEG derived system was used to locally deliver the peptide to the nerve. Using the PEG system, peptide 2 was seen to alleviate pain 10 days post PNL operation compared to the controls. Although there are still many questions that need to be answered about the mechanism of action of peptide 2 and how it can alleviate neuropathic pain, this dissertation served as a starting point to this project.