Myo/Nog cells were discovered in the chick embryo epiblast. Their expression of MyoD reflects a commitment to the skeletal muscle lineage and capacity to differentiate into myofibroblasts. Release of Noggin by Myo/Nog cells is essential for normal morphogenesis. Myo/ Nog cells rapidly respond to wounding in the skin and eyes. In this report, we present evidence suggesting that Myo/Nog cells phagocytose tattoo ink in tissue sections of human skin and engulf cell corpses in cultures of anterior human lens tissue and magnetic beads injected into the anterior chamber of mice in vivo. Myo/Nog cells are distinct from macrophages in the skin and eyes indicated by the absence of labeling with an antibody to ionized calcium binding adaptor molecule 1. In addition to their primary roles as regulators of BMP signaling and progenitors of myofibroblasts, Myo/Nog cells behave as nonprofessional phagocytes defined as cells whose primary functions are unrelated to phagocytosis but are capable of engulfment.

Focal brain injury in the form of a needlestick (NS) results in cell death and induces a self-protective response flanking the lesion. Myo/Nog cells are identified by their expression of bone morphogenetic protein inhibitor Noggin, brain-specific angiogenesis inhibitor 1 (BAI1) and the skeletal muscle specific transcription factor MyoD. Myo/Nog cells limit cell death in two forms of retinopathy. In this study, we examined the acute response of Myo/Nog cells to a NS lesion that extended from the rat posterior parietal cortex to the hippocampus. Myo/Nog cells were identified with antibodies to Noggin and BAI1. These cells were the primary source of both molecules in the uninjured and injured brain. One day after the NS, the normally small population of Myo/Nog cells expanded approximately eightfold within a 1 mm area surrounding the lesion. Myo/Nog cells were reduced by approximately 50% along the lesion with an injection of the BAI1 monoclonal antibody and complement. The number of dying cells, identified by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), was unchanged at this early time point in response to the decrease in Myo/Nog cells. However, increasing the number of Myo/Nog cells within the lesion by injecting BAI1-positive (+) cells isolated from the brains of other animals, significantly reduced cell death and increased the number of NeuN+ neurons compared to brains injected with phosphate buffered saline or exogenous BAI1-negative cells. These findings demonstrate that Myo/Nog cells rapidly react to injury within the brain and increasing their number within the lesion is neuroprotective.

Introduction Retinitis Pigmentosa (RP) is a set of diseases that leads to progressive visual impairment, affecting over one million people worldwide. Despite the heterogeneity of the disease course and mechanism, the various forms of RP all involve progressive loss of retinal rod and cone cells. Myo/Nog cells have been shown to play a crucial role in ocular development. They have been implicated in neuroprotection in response to acute injuries and stress. In this study, we examined the behavior of Myo/Nog cells in a murine model of congenital retinitis pigmentosa (RP), determined the anatomical location of these cells as the degeneration progresses, and assessed their possible role of clearing out the debris caused by the degeneration. Methods C3H/Hej (C3H) mice, which are homozygous for the cGMP phosphodiesterase 6B (PDE6) mutation (also known as the rd1 mutation), were used as the animal model of RP in this study. C3H and C57Bl/6J (C57) control mice were assessed at weeks 2.5, 3, 4, 5, and 6 using scotopic electroretinographs (ERG), ocular computer topography (OCT), and immunofluorescence microscopy. Enucleated eyes were fixed in paraformaldehyde and cryo‐sectioned. Sections were incubated in TUNEL reagent to detect and quantify cell death. Cryosections were labeled with a Myo/Nog specific monoclonal antibody to brain‐specific angiogenesis inhibitor (BAI1). Myo/Nog cell counts were performed by identifying the total number of BAI1+ cells, TUNEL+ cells, and the number of cells that were positive for both BAI1 and TUNEL. Myo/Nog cell counts, photoreceptor counts, outer nuclear layer (ONL), and inner nuclear layer (INL) thicknesses were all obtained using NIS elements software on a FluorScope microscope. Results ERG showed decreased amplitudes of the A and B waves in C3H mice when compared to the C57 group. OCTs demonstrated a significant difference in retinal thickness between the two groups. Progressive thinning of the retina in the C3H mice was confirmed by microscopy. We observed early degeneration of the retina of C3H mice in the central and mid‐peripheral areas before week 2.5, which then progressed more significantly in the edge of the retina in later weeks. Myo/Nog cells were significantly more numerous in C3H mice compared to C57 mice at all time points. Most Myo/Nog cells of C3H mice were found in the outer nuclear layer (ONL) and within the neighboring choroid. Data obtained from ERG and histological demonstrated progressive photoreceptor loss over time, and a rapid decline in ONL/INL thickness between weeks 2.5‐4 in C3H mice. Myo/Nog cells appeared to have phagocytosed cell corpses as evidenced by the overlap in Myo/Nog cell labeling with the labeling of cellular debris (the depleted photoreceptors). Conclusions These findings are consistent with the behaviors of Myo/Nog cells in other forms of retinal stress and injury. Future studies will examine the importance of Myo/Nog cells in clearance in retinopathies.

Introduction Retinopathy of Prematurity (ROP) is the leading cause of blindness in children, affecting 50% of infants born prior to gestational week 32. ROP is the result of postpartum supplemental oxygen administered to compensate for underdeveloped lungs. However, hyperoxia inhibits proper development supplying the retina. When the infants are returned to ambient air, an imbalance is present between the oxygen concentration and metabolic demands of retinal neurons. This leads to a rapid induction of angiogenesis, leaky blood vessels, neovascular tuft formation, and cell death. Myo/Nog cells that express MyoD, Noggin, and brain‐specific angiogenesis inhibitor 1 (BAI1) exhibit neuroprotective properties in the eye and brain and are proposed to play a role in regulating angiogenesis in ROP. Methods An Oxygen‐induced retinopathy (OIR) protocol was implemented in neonatal C57BL/6J mice by exposing them on postnatal days 7‐12 (P7‐P12) to hyperoxia (75% oxygen) and then returning them to normal air (21% oxygen) from P12 until P21. On P15, groups receiving treatments were intravitreally injected with 1 µL of phosphate‐buffered saline (PBS) containing 2000 Myo/Nog cells isolated from the brain with the BAI1 antibody (BAI1+ group), 2000 unsorted brain cells (BAI1‐ group), or PBS alone (PBS group). Electroretinography (ERG) was conducted on P21 to assess retinal function. Eyes were extracted and either dissected for flat‐mount observation of vasculature and tufts, or processed for histology. The thickness of the retina and number of TUNEL+ apoptotic cells were quantified in tissue sections of eyes processed for histology. Adobe Photoshop (Adobe, San Jose, CA) was used to splice together 9 images that made up each whole retina from flat‐mounted eyes. The blood vessels were selected using the “Lasso tool” on photoshop, quantified by number of pixels, and then compared to the total number of pixels in the whole retina. Results OIR induced neovascular tuft formation. Exogenously added Myo/Nog cells normalized the retinopathy induced by the OIR model, reducing the number of tufts and improving the quality of the vasculature. The vasculature was most developed in retinas injected with brain derived Myo/Nog cells. ERG data shows a trend towards improvement of visual function with Myo/Nog cell injection. Conclusion Myo/Nog cell regulation of retinal vascularization may be related to the production of BAI1. Improved visual function seen with injection of Myo/Nog cells may be related to both a reduction of neovascular tufts and direct effects on retinal neurons. Therefore Myo/Nog cells have therapeutic potential in the prevention of ROP by normalizing the vasculature and preventing neuronal cell death.

Background The retina utilizes more oxygen than any other tissue in the body. Photoreceptors located in the retina's outer nuclear layer (ONL) are culled during the “critical period” of eye development when the number of photoreceptors exceeds the supply of oxygen. Retinitis Pigmentosa (RP) is a disease that first affects the rod photoreceptors, causing night blindness and reduced peripheral vision. In mice, RP often starts during the critical period. The objective of this study was to assess the effects of hyperoxia during the critical period on visual function and morphology of the retina in normal mice and mice with RP. Method Thirty five male and female wild‐type (C57BL/6J) mice and 15 mice with an rd1 mutation (C3H/HeJ), which causes a rapidly progressing form of retinitis pigmentosa, were exposed to hyperoxia (75% O₂), hypoxia (12% O₂), and normoxia (21% O₂) from postnatal (P) days 7 to 20. At P26, electroretinography (ERG) was used to assess the visual function of the photoreceptors (A‐wave) and the inner retinal cells (B‐wave). At P27, optical coherence tomography (OCT) and histology were used to observe retinal structure and the effects of the different O₂ groups. For histology, eyes were extracted at P10, P12, P16, and P28. Cell death was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Results In ERGs from C57 mice, both A‐wave and B‐wave amplitudes were significantly lower in the hypoxic condition indicating that hypoxia was detrimental to visual function compared to the normoxic group. OCT data showed that the hyperoxic groups of C57 mice had thicker ONLs compared to the other treatment groups. TUNEL cell counts in the ONL and INL indicated a significant decrease in apoptotic cells during the critical period in the hyperoxic group compared to the hypoxic group. In C3H mice, hyperoxia improved the A and B waves compared to untreated mice. Discussion This study suggests that administration of oxygen during the critical period of retinal development reduces the pruning of cells in the retina and increases visual function in both normal mice and mice with an aggressive form of RP. Oxygen treatment during the critical period of retinal development, which occurs from P8 to P16, may slow retinal degeneration in RP. The effects of hyperoxia on the completion of vascular development must be taken into account when considering the use of hyperoxia therapeutically.