Investigating the role of MMP1 and Ninjurin in glial responses to axotomy

Oregon Health & Science University, Portland OR

Investigators

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Abstract

SUMMARY Neural injury triggers swift responses from glia, including glial migration to injury sites and clearance of damaged neurons through phagocytic engulfment. These innate immune responses are orchestrated, in part, by injury-induced changes in glial gene expression, but we have an incomplete understanding of how transcriptional programs are coupled to the complex cellular responses elicited in response to neural trauma. The core molecular and cellular hallmarks of innate glial immunity are conserved across species. Here, we propose to use well-established axotomy assays, as well as novel in vivo injury paradigms, in adult Drosophila to investigate glial responses to nerve injury; the fly offers a powerful genetic system to manipulate gene expression and function with exquisite cellular and temporal precision in vivo. Our recently published work has identified matrix metalloproteinase 1 (Mmp1) as a novel factor that is robustly upregulated in adult Drosophila glia following nerve injury. Mmp1 facilitates extracellular matrix (ECM) remodeling, glial infiltration of injury sites, and proper clearance of neurotoxic axonal debris. Based on our preliminary work, we hypothesize that secreted Mmp1 targets the adhesion receptor Nerve injury-induced protein (Ninjurin) to promote glial immune activity. In this proposal, we will employ powerful genetic-molecular tools, high-resolution light microscopy, as well as proteomics screening to define how the Draper/Mmp1/Ninjurin pathway contributes to innate glial immune responses to axon degeneration. Specifically, we will (Aim 1) define the functional role of Ninjurin during glial invasion of injury sites and clearance of axon debris and (Aim 2) perform a comprehensive analysis of protein cleavage (the Mmp1 ?degradome?) in adult nervous system tissue after axotomy. Our work will offer a novel framework for understanding how glial proteases drive complex neuroprotective responses from local glial cells in response to neural trauma.