A review of recent developments in retinitis pigmentosa genetics, its clinical features, and natural course

Background: Retinitis pigmentosa (RP), an inherited degenerative ocular disease, is considered the most common type of retinal dystrophy. Abnormalities of the photoreceptors, particularly the rods, and of the retinal pigment epithelium, characterizes this disease. The abnormalities progress from the midperiphery to the central retina. We here reviewed the developments in RP genetics in the last decade, along with its clinical features and natural course. Methods: The present review focused on articles in English language published between January 2008 and February 2020, and deposited in PubMed and Google Scholar databases. We searched for articles reporting on the clinical manifestations and genes related to both syndromic and non-syndromic RP. We screened and analyzed 139 articles, published in the last decade, referring to RP pathogenesis and identified, summarized, and highlighted the most significant genes implicated in either syndromic or non-syndromic RP pathogenesis, causing different clinical manifestations. Results: Recent literature revealed that approximately 80 genes are implicated in non-syndromic RP, and 30 genes in syndromic forms, such as Usher syndrome and Bardet‒Biedl syndrome (BBS). Moreover, it is estimated that 27 genes are implicated in autosomal dominant RP (adRP), 55 genes in autosomal recessive RP (arRP), and 6 genes in X-linked RP (xlRP), causing different RP phenotypes. Characteristically, RHO is the most prevalent adRP- and arRP-causing gene, and RPGR the most common xlRP-causing gene. Other important genes are PRPH2, RP1, CRX, RPE65, ABCA4, CRB1, and USH2Α. However, different phenotypes can also be caused by mutations in the same gene. Conclusions: The genetic heterogeneity of RP necessitates further study to map the exact mutations that cause more severe forms of RP, and to develop and use appropriate genetic or other effective therapies in future

Identification of Ocular Autoantigens Associated With Juvenile Idiopathic Arthritis-Associated Uveitis

The purpose of the current study was to analyze the binding patterns of serum autoantibodies from juvenile idiopathic arthritis (JIA) and JIA-associated uveitis (JIAU) patients to proteomes from different ocular tissues and to identify potential ocular autoantigens in JIAU. Proteomes from porcine iris, ciliary body, or retina tissue were isolated, separated using 2D-gel electrophoresis, and transferred to a blotting membrane. The binding pattern of serum antibodies from JIA or JIAU patients or healthy controls to ocular proteins was visualized by using anti-human IgG secondary antibodies and chemiluminescence reaction. Selected protein spots were excised from silver-stained 2D gels and subjected to mass spectrometry. Serum antibodies binding to ocular proteins were detected in all patient groups and healthy controls. Irrespective of the patient groups, serum antibodies bound to 49 different protein spots of the retina proteome, to 53 of the ciliary body proteome, and to 44 of the iris proteome. The relative binding frequency of sera to these iris protein spots was significantly higher in JIAU than in JIA patients or healthy controls. Particularly in JIAU patients, cluster analyses indicated a broad range of serum antibodies directed against ocular antigens, mostly in the iris proteome. Iris proteins frequently bound by serum antibodies in all groups were identified as tubulin beta chain, vimentin, ATP synthase subunit beta, actin, and L-lactate dehydrogenase B chain. Iris proteins exclusively bound by JIAU serum antibodies were heat shock cognate 71 kDa protein and keratin. Although serum autoantibody binding to ocular antigens was not disease-specific, a significant diversity of autoantibodies against a broad range of antigens, particularly from the iris tissue, was detected in JIAU patients. As the iris is a major site of inflammation in JIAU, the present data give further evidence that autoantibodies may be involved in JIAU immunopathology

Regulation of retinal proteome by topical antiglaucomatous eye drops in an inherited glaucoma rat model.

Examination of the response of the retinal proteome to elevated intraocular pressure (IOP) and to the pharmacological normalization of IOP is crucial, in order to develop drugs with neuroptorective potential. We used a hereditary rat model of ocular hypertension to lower IOP with travaprost and dorzolamide applied topically on the eye surface, and examine changes of the retinal proteome. Our data demonstrate that elevated IOP causes alterations in the retinal protein profile, in particular in high-mobility-group-protein B1 (HMGB1), calmodulin, heat-shock-protein (HSP) 70 and carbonic anhydrase II expression. The changes of the retinal proteome by dorzolamide or travoprost are different and independent of the IOP lowering effect. This fact suggests that the eye drops exert a direct IOP-independent effect on retinal metabolism. Further investigations are required to elucidate the potential neuroprotective mechanisms signaled through changes of HMGB1, calmodulin, HSP70 and carbonic anhydrase II expression in glaucoma. The data may facilitate development of eye drops that exert neuroprotection through direct pharmacological effect

Cataractogenic lens injury prevents traumatic ganglion cell death and promotes axonal regeneration

PURPOSE. To examine and quantify neuroprotective and neurite-promoting activity on retinal ganglion cells (RGCs) after injury of the lens. METHODS. In adult albino rats, penetrating lens injury was performed by intraocular injection. To test for injury-induced neuroprotective effects in vivo, fluorescence-prelabeled RGCs were axotomized by subsequent crush of the optic nerve (ON) with concomitant lens injury to cause cataract. The numbers of surviving RGCs were determined in retinal wholemounts and compared between the different experimental and control groups. To examine axonal regeneration in vivo, the ON was cut and replaced with an autologous piece of sciatic nerve (SN). Retinal ganglion cells with axons that had regenerated within the SN under lens injury or control conditions were retrogradely labeled with a fluorescent dye and counted on retinal wholemounts. Neurite regeneration was also studied in adult retinal explants obtained either after lens injury or without injury. The numbers of axons were determined after 1 and 2 days in culture. Putative neurotrophins (NTs) were studied within immunohistochemistry and Western blot analysis. RESULTS. Cataractogenic lens injury performed at the same time as ON crush resulted in highly significant rescue of 746 Ϯ 126 RGCs/mm 2 (mean Ϯ SD; approximately 39% of total RGCs) 14 days after injury compared with controls without injury or with injection of buffer into the vitreous body (30 Ϯ 18 RGCs/mm 2 ). When lens injury was performed with a delay of 3 days after ON crush, 49% of RGCs survived, whereas delay of 5 days still rescued 45% of all RGCs. In the grafting paradigm virtually all surviving RGCs after lens injury appeared to have regenerated an axon within the SN graft (763 Ϯ 114 RGCs/mm 2 versus 79 Ϯ 17 RGCs/mm 2 in controls). This rate of regeneration corresponds to approximately 40% of all RGCs. In the regeneration paradigm in vitro preceding lens injury and ON crush 5 days previous resulted in a maximum of regeneration of 273 Ϯ 39 fibers/explant after 1 day and 574 Ϯ 38 fibers/explant after 2 days in vitro. In comparison, in control retinal pieces without lens injury 28 Ϯ 13 fibers/explant grew out at 1 day, and 97 Ϯ 37 fibers/explant grew out at 2 days in culture. Immunohistochemical and Western blot analysis of potential NTs in the injured lens revealed no expression of ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF), NT-4, nerve growth factor (NGF), and basic fibroblast growth factor (bFGF). CONCLUSIONS. The findings indicate that the lens contains high neuroprotective and neuritogenic activity, which is not caused by NT. Compared with the data available in the literature, this neuroprotection is quantitatively among the highest ever reported within the adult rat visual system. (Invest Ophthalmol Vis Sci. 2000;41:3943-3954

Crystallins are regulated biomarkers for monitoring topical therapy of glaucomatous optic neuropathy.

Optic nerve atrophy caused by abnormal intraocular pressure (IOP) remains the most common cause of irreversible loss of vision worldwide. The aim of this study was to determine whether topically applied IOP-lowering eye drugs affect retinal ganglion cells (RGCs) and retinal metabolism in a rat model of optic neuropathy. IOP was elevated through cauterization of episcleral veins, and then lowered either by the daily topical application of timolol, timolol/travoprost, timolol/dorzolamide, or timolol/brimonidine, or surgically with sectorial iridectomy. RGCs were retrogradely labeled 4 days prior to enucleation, and counted. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), matrix-assisted laser desorption ionization mass spectrometry, Western blotting, and immunohistochemistry allowed the identification of IOP-dependent proteomic changes. Genomic changes were scrutinized using microarrays and qRT-PCR. The significant increase in IOP induced by episcleral vein cauterization that persisted until 8 weeks of follow-up in control animals (p<0.05) was effectively lowered by the eye drops (p<0.05). As anticipated, the number of RGCs decreased significantly following 8 weeks of elevated IOP (p<0.05), while treatment with combination compounds markedly improved RGC survival (p<0.05). 2D-PAGE and Western blot analyses revealed an IOP-dependent expression of crystallin cry-βb2. Microarray and qRT-PCR analyses verified the results at the mRNA level. IHC demonstrated that crystallins were expressed mainly in the ganglion cell layer. The data suggest that IOP and either topically applied antiglaucomatous drugs influence crystallin expression within the retina. Neuronal crystallins are thus suitable biomarkers for monitoring the progression of neuropathy and evaluating any neuroprotective effects

Elongation of axons during regeneration involves retinal crystallin beta b2 (crybb2).

Adult retinal ganglion cells (RGCs) can regenerate their axons in vitro. Using proteomics, we discovered that the supernatants of cultured retinas contain isoforms of crystallins with crystallin beta b2 (crybb2) being clearly up-regulated in the regenerating retina. Immunohistochemistry revealed the expression of crybb within the retina, including in filopodial protrusions and axons of RGCs. Cloning and overexpression of crybb2 in RGCs and hippocampal neurons increased axonogenesis, which in turn could be blocked with antibodies against beta-crystallin. Conditioned medium from crybb2-transfected cell cultures also supported the growth of axons. Finally real time imaging of the uptake of green fluorescent protein-tagged crybb2 fusion protein showed that this protein becomes internalized. These data are the first to show that axonal regeneration is related to crybb2 movement. The results suggest that neuronal crystallins constitute a novel class of neurite-promoting factors that likely operate through an autocrine mechanism and that they could be used in neurodegenerative diseases