Retinal response to systemic inflammation differs between sexes and neurons.

Background: Neurological dysfunction and glial activation are common in severe infections such as sepsis. There is a sexual dimorphism in the response to systemic inflammation in both patients and animal models, but there are few comparative studies. Here, we investigate the effect of systemic inflammation induced by intraperitoneal administration of lipopolysaccharide (LPS) on the retina of male and female mice and determine whether antagonism of the NLRP3 inflammasome and the extrinsic pathway of apoptosis have protective effects on the retina. Methods: A single intraperitoneal injection of LPS (5 mg/kg) was administered to two months old C57BL/6J male and female mice. Retinas were examined longitudinally in vivo using electroretinography and spectral domain optical coherence tomography. Retinal ganglion cell (RGC) survival and microglial activation were analysed in flat-mounts. Retinal extracts were used for flow cytometric analysis of CD45 and CD11b positive cells. Matched plasma and retinal levels of proinflammatory cytokines were measured by ELISA. Retinal function and RGC survival were assessed in animals treated with P2X7R and TNFR1 antagonists alone or in combination. Results: In LPS-treated animals of both sexes, there was transient retinal dysfunction, loss of vision-forming but not non-vision forming RGCs, retinal swelling, microglial activation, cell infiltration, and increases in TNF and IL-1ß. Compared to females, males showed higher vision-forming RGC death, slower functional recovery, and overexpression of lymphotoxin alpha in their retinas. P2X7R and TNFR1 antagonism, alone or in combination, rescued vision-forming RGCs. P2X7R antagonism also rescued retinal function. Response to treatment was better in females than in males. Conclusions: Systemic LPS has neuronal and sex-specific adverse effects in the mouse retina, which are counteracted by targeting the NLRP3 inflammasome and the extrinsic pathway of apoptosis. Our results highlight the need to analyse males and females in preclinical studies of inflammatory diseases affecting the central nervous system.

The retina of the lab rat: focus on retinal ganglion cells and photoreceptors.

Albino and pigmented rat strains are widely used in models to study retinal degeneration and to test new therapies. Here, we have summarized the main topographical and functional characteristics of the rat retina focussing on photoreceptors and retinal ganglion cells (RGCs), the beginning and end of the retinal circuitry, respectively. These neurons are very sensitive to injury and disease, and thus knowing their normal number, topography, and function is essential to accurately investigate on neuronal survival and protection.

Axonal Injuries Cast Long Shadows: Long Term Glial Activation in Injured and Contralateral Retinas after Unilateral Axotomy.

BACKGROUND: To analyze the course of microglial and macroglial activation in injured and contralateral retinas after unilateral optic nerve crush (ONC). METHODS: The left optic nerve of adult pigmented C57Bl/6 female mice was intraorbitally crushed and injured, and contralateral retinas were analyzed from 1 to 45 days post-lesion (dpl) in cross-sections and flat mounts. As controls, intact retinas were studied. Iba1+ microglial cells (MCs), activated phagocytic CD68+MCs and M2 CD206+MCs were quantified. Macroglial cell changes were analyzed by GFAP and vimentin signal intensity. RESULTS: After ONC, MC density increased significantly from 5 to 21 dpl in the inner layers of injured retinas, remaining within intact values in the contralateral ones. However, in both retinas there was a significant and long-lasting increase of CD68+MCs. Constitutive CD206+MCs were rare and mostly found in the ciliary body and around the optic-nerve head. While in the injured retinas their number increased in the retina and ciliary body, in the contralateral retinas decreased. Astrocytes and Müller cells transiently hypertrophied in the injured retinas and to a lesser extent in the contralateral ones. CONCLUSIONS: Unilateral ONC triggers a bilateral and persistent activation of MCs and an opposed response of M2 MCs between both retinas. Macroglial hypertrophy is transient.

Neuronal Death in the Contralateral Un-Injured Retina after Unilateral Axotomy: Role of Microglial Cells.

For years it has been known that unilateral optic nerve lesions induce a bilateral response that causes an inflammatory and microglial response in the contralateral un-injured retinas. Whether this contralateral response involves retinal ganglion cell (RGC) loss is still unknown. We have analyzed the population of RGCs and the expression of several genes in both retinas of pigmented mice after a unilateral axotomy performed close to the optic nerve head (0.5 mm), or the furthest away that the optic nerve can be accessed intraorbitally in mice (2 mm). In both retinas, RGC-specific genes were down-regulated, whereas caspase 3 was up-regulated. In the contralateral retinas, there was a significant loss of 15% of RGCs that did not progress further and that occurred earlier when the axotomy was performed at 2 mm, that is, closer to the contralateral retina. Finally, the systemic treatment with minocycline, a tetracycline antibiotic that selectively inhibits microglial cells, or with meloxicam, a non-steroidal anti-inflammatory drug, rescued RGCs in the contralateral but not in the injured retina. In conclusion, a unilateral optic nerve axotomy triggers a bilateral response that kills RGCs in the un-injured retina, a death that is controlled by anti-inflammatory and anti-microglial treatments. Thus, contralateral retinas should not be used as controls.

Mesenchymal stromal cell therapy for damaged retinal ganglion cells, is gold all that glitters?

Mesenchymal stromal cells are an excellent source of stem cells because they are isolated from adult tissues or perinatal derivatives, avoiding the ethical concerns that encumber embryonic stem cells. In preclinical models, it has been shown that mesenchymal stromal cells have neuroprotective and immunomodulatory properties, both of which are ideal for central nervous system treatment and repair. Here we will review the current literature on mesenchymal stromal cells, focusing on bone marrow mesenchymal stromal cells, adipose-derived mesenchymal stromal cells and mesenchymal stromal cells from the umbilical cord stroma, i.e., Wharton's jelly mesenchymal stromal cells. Finally, we will discuss the use of these cells to alleviate retinal ganglion cell degeneration following axonal trauma.