Role of Arginase 1 in Retinal Ischemia Reperfusion Injury

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Abstract of the parent grant R00EY029373: Retinal ischemia is a major cause of vision loss in common retinal disease conditions including diabetic retinopathy, glaucoma, retinopathy of prematurity, and vein occlusion. This project aims to define the mechanisms of retinal ischemic injury and identify new therapeutic targets. We have previously demonstrated the involvement of the arginase enzyme in retinal neurovascular diseases. Arginase has two isoforms. Building upon the lab's finding that the mitochondrial isoform, arginase 2 (A2), has a deleterious role in retinal ischemia-reperfusion (IR) injury, we developed a project focusing on the neurovascular protective role of the cytosolic isoform arginase 1 (A1). Our recently published papers shows a neuroprotective role of A1 expression in myeloid cells. Arginase competes with nitric oxide synthase (NOS) for their common substrate L-arginine. Nitric oxide (NO) produced by inducible NOS (iNOS) causes neurovascular degeneration. We predict that A1 upregulation in myeloid cells limits iNOS-derived nitrative and oxidative stress and reduces inflammation through its downstream metabolites ornithine and putrescine. Putrescine is the precursor of polyamines and it is formed from ornithine by ornithine decarboxylase (ODC, the rate-limiting enzyme in polyamine biosynthesis). These metabolites have been shown to promote reparative myeloid cells through chromatin modification. In line with this, our preliminary data show that histone deacetylase (HDAC) 3 is increased in the absence of A1 in both IR-injured retinas and stimulated macrophages. HDAC3 is essential for macrophage inflammatory gene transcription and it has been shown to suppress A1 expression. Herein, We propose a novel suppressive effect of A1 on HDAC3. Our central hypothesis predicts that myeloid A1 protects against retinal IR injury through ODC-mediated suppression of HDAC3. We will be using mice with myeloid-specific deletion of A1, ODC and HDAC3, as well as the investigational drug, BCT-100 (a PEGylated form of arginase 1), together with primary macrophages isolation and treatment with inhibitors for HDAC3 or arginase downstream enzyme, ODC. Our goal is to achieve the following objectives: First) Determine the effect of manipulating the arginase pathway on myeloid cells infiltration / activation in retinal IR injury and the therapeutic potential of BCT- 100. Second) Describe the cross talk between the arginase pathway and HDAC3 and determine whether A1 in myeloid cells mediates its protective effect through suppression of HDAC3. Third) Determine the role of myeloid specific deletion of HDAC3 on macrophage inflammatory response and retinal neurovascular injury.