Retinal Ganglion Cells

Pathological tau isoforms, including hyperphosphorylated tau at serine 396 (pS396-tau) and tau oligomers (Oligo-tau), are elevated in the retinas of patients with mild cognitive impairment (MCI) due to Alzheimer's disease (AD) and AD dementia. These patients exhibit significant retinal ganglion cell (RGC) loss, however the presence of tau isoforms in RGCs and their impact on RGC integrity, particularly in early AD, have not been studied. Here, we analyzed retinal superior temporal cross-sections from 25 MCI or AD patients and 16 age- and sex-matched cognitively normal controls. Using the RGC marker ribonucleic acid binding protein with multiple splicing (RBPMS) and Nissl staining, we found a 46-56% reduction in RBPMS+ RGCs and Nissl+ neurons in the ganglion cell layer (GCL) of MCI and AD retinas (P + and Oligo-tau+ RGC counts were significantly increased by 2.1-3.5-fold in MCI and AD retinas versus control retinas (P P=0.85, P P=-0.40-(-0.64), P + RGCs in the central and mid-periphery showed the closest associations with disease status, while Oligo-tau+ RGCs in the mid-periphery exhibited the strongest correlations with brain pathology (NFTs, Braak stages, ABC scores; rS=0.78-0.81, P S=-0.79, P = 0.0019). Overall, these findings identify a link between pathogenic tau in RGCs and RGC degeneration in AD, involving apoptotic and GVD-necroptotic cell death pathways. Future research should validate these results in larger and more diverse cohorts and develop RGC tauopathy as a potential noninvasive biomarker for early detection and monitoring of AD progression.

The retina transforms patterns of light into visual feature representations supporting behaviour. These representations are distributed across various types of retinal ganglion cells (RGCs), whose spatial and temporal tuning properties have been studied extensively in many model organisms, including the mouse. However, it has been difficult to link the potentially nonlinear retinal transformations of natural visual inputs to specific ethological purposes. Here, we discover a nonlinear selectivity to chromatic contrast in an RGC type that allows the detection of changes in visual context. We trained a convolutional neural network (CNN) model on large-scale functional recordings of RGC responses to natural mouse movies, and then used this model to search in silico for stimuli that maximally excite distinct types of RGCs. This procedure predicted centre colour opponency in transient suppressed-by-contrast (tSbC) RGCs, a cell type whose function is being debated. We confirmed experimentally that these cells indeed responded very selectively to Green-OFF, UV-ON contrasts. This type of chromatic contrast was characteristic of transitions from ground to sky in the visual scene, as might be elicited by head or eye movements across the horizon. Because tSbC cells performed best among all RGC types at reliably detecting these transitions, we suggest a role for this RGC type in providing contextual information (i.e. sky or ground) necessary for the selection of appropriate behavioural responses to other stimuli, such as looming objects. Our work showcases how a combination of experiments with natural stimuli and computational modelling allows discovering novel types of stimulus selectivity and identifying their potential ethological relevance.

Glaucoma is a neurodegenerative disorder marked by the loss of retinal ganglion cells (RGCs) and axonal degeneration, resulting in irreversible vision impairment. While intraocular pressure (IOP) is presently acknowledged as the sole modifiable risk factor, the sensitivity of RGCs to IOP varies among individuals. Consequently, progressive vision loss may ensue even when IOP is effectively managed. This review consolidates current knowledge regarding the pathogenesis of RGCs in glaucoma and various neurodegenerative diseases. It delves into the mechanisms underlying RGC transsynaptic degeneration and axonal defects in glaucoma from a pathophysiological standpoint, and it elucidates the alterations in the visual pathway throughout the progression of the disease. Furthermore, the article outlines neuroprotective and nerve regeneration strategies aimed at vision restoration in glaucoma patients, offers insights for clinical management of the condition, and investigates prospective avenues for gene therapy.

BackgroundProgressive loss of retinal ganglion cells (RGCs) and degeneration of optic nerve (ON) axons are the key pathological hallmarks of glaucoma, the leading cause of irreversible blindness. Elevated intraocular pressure (IOP), primarily due to dysfunction of the trabecular meshwork (TM), remains the most significant and only known modifiable risk factor. However, vision loss persists in some patients despite effective IOP control, highlighting the critical need to elucidate the mechanisms driving glaucomatous neurodegeneration. Emerging evidence links mitochondrial dysfunction to glaucomatous neurodegeneration, yet the precise mechanisms remain poorly defined. Here, we investigate whether defective autophagy/mitophagy, which removes damaged mitochondria, contributes to mitochondrial accumulation, oxidative stress, and neurodegeneration in glaucoma. We further explore the therapeutic potential of enhancing autophagy to improve mitochondrial turnover, mitigate RGC loss, and preserve visual function.MethodsGlucocorticoid (GC)-induced and myocilin (MYOC)-associated glaucoma mouse models were used to assess the expression of mitochondrial markers (TOM20/COX IV), oxidative DNA damage (8-OHdG), and mitophagy/autophagy-related proteins (p62, LC3, Phospho-ubiquitin (Ser65), and LAMP1) in retinal tissues. Transmission electron microscopy (TEM) was employed to analyze mitochondrial accumulation in glaucomatous ON. Mitophagy flux was assessed at early and late stages of neurodegeneration using mitophagy reporter Mt-Keima mice. The effect of RGC-specific autophagy deficiency on mitochondrial accumulation and neurodegeneration was further investigated using Atg5flox/flox mice, in which Atg5 deletion was induced by AAV2-Cre delivery. Additionally, the therapeutic effect of enhancing autophagy with Torin 2 to restore mitochondrial turnover and prevent glaucomatous neurodegeneration was evaluated in both GC-induced and myocilin-associated glaucoma models, as well as in ex vivo human retinal explants.ResultsChronic IOP elevation led to increased mitochondrial accumulation, oxidative DNA damage, and impaired mitophagy/autophagy in glaucomatous retina. TEM analysis further confirmed the accumulation of structurally abnormal mitochondria in glaucomatous ON. In Mt-Keima mice, chronic IOP elevation significantly reduced mitophagy flux prior to RGC loss, indicating that mitophagy impairment precedes neurodegeneration. RGC-specific Atg5 deletion induced the accumulation of damaged mitochondria, leading to neurodegeneration in Atg5 flox/flox mice. Notably, pharmacological restoration of impaired autophagy with Torin 2 prevented mitochondrial accumulation and preserved the structural and functional integrity of RGCs and their axons in glaucoma mouse models and ex vivo human retinal explant cultures.ConclusionOur study indicates impaired autophagy contributes to damaged mitochondrial accumulation and oxidative stress, leading to glaucomatous neurodegeneration. Enhancing autophagy in RGCs represents a promising therapeutic strategy to prevent glaucomatous neurodegeneration.