P58^IPK is a multifaceted endoplasmic reticulum (ER) chaperone and a regulator of eIF2α kinases involved in a wide range of cellular processes including protein synthesis, ER stress response, and macrophage-mediated inflammation. Systemic deletion of p58^IPK leads to age-related loss of retinal ganglion cells (RGC) and exacerbates RGC damage induced by ischemia/reperfusion and increased intraocular pressure (IOP), suggesting a protective role of p58^IPK in the retina. However, the mechanisms remain elusive. Herein, we investigated the cellular mechanisms underlying the neuroprotection action of p58^IPK using conditional knockout (cKO) mouse lines where p58^IPK is deleted in retinal neurons (Chx10-p58^IPK cKO) or in myeloid cells (Lyz2-p58^IPK cKO). In addition, we overexpressed p58^IPK by adeno-associated virus (AAV) in the retina to examine the effect of p58^IPK on RGC survival after ocular hypertension (OHT) in wild type (WT) mice. Our results show that overexpression of p58^IPK by AAV significantly improved RGC survival after OHT in WT mice, suggesting a protective effect of p58^IPK on reducing RGC injury. Conditional knockout of p58^IPK in retinal neurons or in myeloid cells did not alter retinal structure or cellular composition. However, a significant reduction in the b wave of light-adapted electroretinogram (ERG) was observed in Chx10-p58^IPK cKO mice. Deletion of p58^IPK in retinal neurons exacerbates RGC loss at 14 days after OHT. In contrast, deficiency of p58^IPK in myeloid cells increased the microglia/macrophage activation but had no effect on RGC loss. We conclude that deletion of p58^IPK in macrophages increases their activation, but does not influence RGC survival. These results suggest that the neuroprotective action of p58^IPK is mediated by its expression in retinal neurons, but not in macrophages. Therefore, targeting p58^IPK specifically in retinal neurons is a promising approach for the treatment of neurodegenerative retinal diseases including glaucoma.

During development, retinal progenitor cells (RPCs) take on different trajectories for distinct cell fates. Previous studies have identified key regulators involved in two key steps of retinal ganglion cell (RGC) genesis; Atoh7 functions in a subpopulation of RPCs to render them competent for the RGC fate, whereas Pou4f2 and Isl1 function to specify the RGC fate and promote RGC differentiation. Extensive research has been performed on the roles of these transcription factors in RGC development, but properties of these two phases they represent and the cellular context in which these two factors function have not been thoroughly investigated, largely due to the cellular heterogeneity of developing retina. In this paper, we describe two novel knock-in mouse alleles, Atoh7 ^{zsGreenCreERT2} and Pou4f2 ^FlagtdTomato , which enabled us to label retinal cells in the two phases of RGC development by fluorescent proteins. In addition, the Atoh7 ^{zsGreenCreERT2} allele also allowed for indirect labeling of RGCs and other cell types upon tamoxifen induction in a dose-dependent manner. Further, these alleles could be used to purify retinal cells of these different phases by fluorescence assisted cell sorting (FACS). Thus, these two alleles can serve as very useful tools for studying the molecular and genetic mechanisms underlying RGC formation.

Choroideremia is a rare X-linked recessive retinal disorder characterized by progressive vision loss caused by retinal degeneration resulting from mutations in the CHM gene, which encodes Rab escort protein 1 (REP-1). In humans and mice, the Rab escort protein (REP) family consists of two members, REP-1 and REP-2, with REP-2 hypothesized to compensate for REP-1 deficiency in tissues outside the eye in choroideremia. In this study, we conducted a systematic mutational analysis of the mouse orthologs of REP-1 and REP-2. Blood analyses revealed metabolic abnormalities in the mutant mice deficient for REP-1, resembling the systemic metabolic disturbances observed in individuals with choroideremia, such as altered lipid and hemoglobin metabolism. We also observed an elevation in systemic inflammatory biomarkers in these mutant mice. Interestingly, these systemic abnormalities emerged before retinal degeneration became detectable in REP-1-deficient mice. Transcriptomic analysis of retinas isolated from REP-1 deficient mice revealed enrichment of proinflammatory signaling pathways. These results suggest important similarities between choroideremia and some forms of retinitis pigmentosa. While engineered loss of REP-2 alone caused no detectable phenotypic changes, dual deficiency in REP-1 and REP-2 resulted in lethality under both in vivo and in vitro conditions. Our findings offer novel insights into REPs and deepen our understanding of choroideremia, which may contribute to the development of new treatments for this genetic condition.