Müller Cell Molecular Heterogeneity: Facts and Predictions

Homer1a reduces inflammatory response after retinal ischemia/reperfusion injury

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Elevated intraocular pressure (IOP) is one of the causes of retinal ischemia/reperfusion injury, which results in NLRP3 inflammasome activation and leads to visual damage. Homer1a is reported to play a protective role in neuroinflammation in the cerebrum. However, the effects of Homer1a on NLRP3 inflammasomes in retinal ischemia/reperfusion injury caused by elevated IOP remain unknown. In our study, animal models were constructed using C57BL/6J and Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice with elevated IOP-induced retinal ischemia/reperfusion injury. For in vitro experiments, the oxygen-glucose deprivation/reperfusion injury model was constructed with Müller cells. We found that Homer1a overexpression ameliorated the decreases in retinal thickness and Müller cell viability after ischemia/reperfusion injury. Furthermore, Homer1a knockdown promoted NF-κB P65Ser536 activation via caspase-8, NF-κB P65 nuclear translocation, NLRP3 inflammasome formation, and the production and processing of interleukin-1β and interleukin-18. The opposite results were observed with Homer1a overexpression. Finally, the combined administration of Homer1a protein and JSH-23 significantly inhibited the reduction in retinal thickness in Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice and apoptosis in Müller cells after ischemia/reperfusion injury. Taken together, these studies demonstrate that Homer1a exerts protective effects on retinal tissue and Müller cells via the caspase-8/NF-κB P65/NLRP3 pathway after I/R injury.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Glial cells as a promising therapeutic target of glaucoma: beyond the IOP

Glial cells, a type of non-neuronal cell found in the central nervous system (CNS), play a critical role in maintaining homeostasis and regulating CNS functions. Recent advancements in technology have paved the way for new therapeutic strategies in the fight against glaucoma. While intraocular pressure (IOP) is the most well-known modifiable risk factor, a significant number of glaucoma patients have normal IOP levels. Because glaucoma is a complex, multifactorial disease influenced by various factors that contribute to its onset and progression, it is imperative that we consider factors beyond IOP to effectively prevent or slow down the disease's advancement. In the realm of CNS neurodegenerative diseases, glial cells have emerged as key players due to their pivotal roles in initiating and hastening disease progression. The inhibition of dysregulated glial function holds the potential to protect neurons and restore brain function. Consequently, glial cells represent an enticing therapeutic candidate for glaucoma, even though the majority of glaucoma research has historically concentrated solely on retinal ganglion cells (RGCs). In addition to the neuroprotection of RGCs, the proper regulation of glial cell function can also facilitate structural and functional recovery in the retina. In this review, we offer an overview of recent advancements in understanding the non-cell-autonomous mechanisms underlying the pathogenesis of glaucoma. Furthermore, state-of-the-art technologies have opened up possibilities for regenerating the optic nerve, which was previously believed to be incapable of regeneration. We will also delve into the potential roles of glial cells in the regeneration of the optic nerve and the restoration of visual function.

Retinal gliosis and phenotypic diversity of intermediate filament induction and remodeling upon acoustic blast overpressure (ABO) exposure to the rat eye

Traumatic brain injury (TBI) caused by acoustic blast overpressure (ABO) is frequently associated with chronic visual deficits in military personnel and civilians. In this study, we characterized retinal gliotic response in adult male rats following a single ABO exposure directed to one side of the head. Expression of gliosis markers and intermediate filaments was assessed at 48 h and 1 wk post-ABO exposure, in comparison to age-matched non-exposed control retina. In response to a single ABO exposure, type III IF, glial fibrillary acidic protein (GFAP) was variably induced in a subpopulation of retinal Müller glia in ipsilateral eyes. ABO-exposed eyes exhibited radial Müller glial GFAP filament extension through the inner plexiform layer (IPL) and the inner nuclear layer (INL) through the retina in both the nasal quadrant and juxta-optic nerve head (jONH) eye regions at 1 wk post-ABO. We observed an ∼6-fold increase (p ≤ 0.05) in radial glial GFAP immunolabeling in the IPL in both eye regions, in comparison to regionally matched controls. Similarly, GFAP extension through the INL into the outer retina was elevated ∼3-fold, p ≤ 0.05 in the nasal retina, but exhibited wider variability in the jONH retina. In contrast, constitutive type III IF vimentin exhibited greater remodeling in retinal Müller glia through the jONH retina compared to the nasal retina in response to ABO. We observed areas of lateral vimentin remodeling through the Müller glial end-feet, and greater mid-outer retinal radial vimentin IF extension in a subpopulation of glia at 1 wk post-ABO. We also observed a significant increase in total retinal levels of the type III IF desmin in ABO-exposed retina vs. controls (∼1.6-fold, p ≤ 0.01). In addition, ABO-exposure elicited varied glial induction of developmentally regulated type VI family IFs (nestin and synemin) in subpopulations of Müller cells at 48 h and 1 wk post-ABO. We demonstrate that multiple glial phenotypes emerge in the rat retina following a single ABO exposure, rather than a global homogeneous retinal glial response, involving less well characterized IF protein forms which warrant further investigation in the context of ABO-induced retinal gliosis.