The retinal ganglion cells (RGCs) are the output cells of the retina into the brain. In mammals, these cells are not able to regenerate their axons after optic nerve injury, leaving the patients with optic neuropathies with permanent visual loss. An effective RGCs-directed therapy could provide a beneficial effect to prevent the progression of the disease. Axonal injury leads to the functional loss of RGCs and subsequently induces neuronal death, and axonal regeneration would be essential to restore the neuronal connectivity, and to reestablish the function of the visual system. The manipulation of several intrinsic and extrinsic factors has been proposed in order to stimulate axonal regeneration and functional repairing of axonal connections in the visual pathway. However, there is a missing point in the process since, until now, there is no therapeutic strategy directed to promote axonal regeneration of RGCs as a therapeutic approach for optic neuropathies.

RNA binding protein with multiple splicing (RBPMS) is expressed exclusively in retinal ganglion cells (RGCs) in the retina and can label all RGCs in normal retinas of mice, rats, guinea pigs, rabbits, cats, and monkeys, but its function in these cells is not known. As a result of the limited knowledge regarding RBPMS, we analyzed the expression of RBPMS in the retina of different mammalian species (humans, pigs, and rats), in various stages of development (neonatal and adult) and with different levels of injury (control, hypoxia, and organotypic culture or explants). In control conditions, RBPMS was localized in the RGCs somas in the ganglion cell layer, whereas in hypoxic conditions, it was localized in the RGCs dendrites in the inner plexiform layer. Such differential distributions of RBPMS occurred in all analyzed species, and in adult and neonatal retinas. Furthermore, we demonstrate RBPMS localization in the degenerating RGCs axons in the nerve fiber layer of retinal explants. This is the first evidence regarding the possible transport of RBPMS in response to physiological damage in a mammalian retina. Therefore, RBPMS should be further investigated in relation to its role in axonal and dendritic degeneration.

Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease. In this study, the tear proteome profile of patients with idiopathic PD (iPD, n = 24), carriers of the E46K-SNCA mutation (n = 3) and healthy control (CT, n = 27) subjects was analyzed to identify candidate biomarkers for the diagnosis of PD. An observational, prospective and case-control pilot study was carried out, analyzing the participants tear samples by nano-liquid chromatography–mass spectrometry (nLC–MS/MS) and assessing their neurological impairment. The proteomic data obtained are available at ProteomeXchange with identifier 10.6019/PXD028811. These analyses led to the identification of 560 tear proteins, some of which were deregulated in PD patients and that have been implicated in immune responses, inflammation, apoptosis, collagen degradation, protein synthesis, defense, lipid transport and altered lysosomal function. Of these proteins, six were related to neurodegenerative processes and showed a good capacity to classify patients and controls. These findings revealed that certain proteins were upregulated in the tears of PD patients, mainly proteins involved in lysosomal function. Thus, in this study, tear proteins were identified that are implicated in neurodegeneration and that may be related to an aggressive disease phenotype in PD patients.

The eye of the largest adult mammal in the world, the whale, offers a unique opportunity to study the evolution of the visual system and its adaptation to aquatic environments. However, the difficulties in obtaining cetacean samples mean these animals have been poorly studied. Thus, the aim of this study was to characterise the different neurons and glial cells in the whale retina by immunohistochemistry using a range of molecular markers. The whale retinal neurons were analysed using different antibodies, labelling retinal ganglion cells (RGCs), photoreceptors, bipolar and amacrine cells. Finally, glial cells were also labelled, including astrocytes, Müller cells and microglia. Thioflavin S was also used to label oligomers and plaques of misfolded proteins. Molecular markers were used to label the specific structures in the whale retinas, as in terrestrial mammalian retinas. However, unlike the retina of most land mammals, whale cones do not express the cone markers used. It is important to highlight the large size of whale RGCs. All the neurofilament (NF) antibodies used labelled whale RGCs, but not all RGCs were labelled by all the NF antibodies used, as it occurs in the porcine and human retina. It is also noteworthy that intrinsically photosensitive RGCs, labelled with melanopsin, form an extraordinary network in the whale retina. The M1, M2, and M3 subtypes of melanopsin positive-cells were detected. Degenerative neurite beading was observed on RGC axons and dendrites when the retina was analysed 48 h post-mortem. In addition, there was a weak Thioflavin S labelling at the edges of some RGCs in a punctuate pattern that possibly reflects an early sign of neurodegeneration. In conclusion, the whale retina differs from that of terrestrial mammals. Their monochromatic rod vision due to the evolutionary loss of cone photoreceptors and the well-developed melanopsin-positive RGC network could, in part, explain the visual perception of these mammals in the deep sea.

Retinal ganglion cells (RGCs) transmit visual information to the brain and are selectively affected in glaucoma, a neurodegenerative disease caused by increased intraocular pressure (IOP) leading to vision loss. Not all RGC subtypes are equally vulnerable; thus, this study aimed to comprehensively analyze the differential loss of RGC subtypes using a rat model of chronic glaucoma. A chronic glaucoma model was established by cauterizing three episcleral veins in rat eyes. IOP was measured using an applanation tonometer, and after 40 days animals were euthanized. Whole-mount retinas were immunostained. RGCs were labeled with anti-RNA-binding protein with multiple splicing (RBPMS; marks 100% of RGCs) and co-labeled with subtype-specific antibodies: CART, melanopsin (OPN4), Foxp2, Islet1/2, SPP1, and Tbr2. RGC loss and subtype distribution were quantified as percentages of RBPMS-positive cells in different retinal regions. In glaucomatous eyes, RGC survival decreased in the retinal periphery, with 65.44% in the dorsal-nasal and 76.03% in the ventral-temporal regions. CART-positive RGCs dropped from 32.9% ± 5.15% to 20.26% ± 2.64% (dorsal-nasal) and from 33.07% ± 4.09% to 22.65% ± 2.65% (ventral-temporal), indicating higher vulnerability. In contrast, OPN4-positive RGCs increased from 3.27% ± 1.34% to 6.99% ± 2.31% (dorsal-nasal), suggesting greater intrinsically photosensitive RGC (ipRGC) resilience. Percentages of SPP1-, Foxp2-, Islet1/2-, and Tbr2-positive RGCs remained unchanged, suggesting proportional loss to total RGC reduction. RGC subtypes showed differing susceptibilities to IOP, with OPN4-positive RGCs (ipRGCs) being more resistant and CART-positive RGCs (ON-OFF direction-selective ganglion cells [ooDSGCs]) highly vulnerable. This highlights the need to study ooDSGC degeneration and explore targeted neuroprotection. Future research should develop therapies to protect, regenerate, or replace ooDSGCs.