Dysfunction of the retinal pigment epithelium (RPE) is associated with several diseases characterized by retinal degeneration, such as diabetic retinopathy (DR). However, it has recently been proposed that outer retinal neurons also participate in the damage triggering. Therefore, we have evaluated possible crosstalk between RPE and photoreceptors in priming and maintaining oxi-dative damage of the RPE. For this purpose, we used ARPE-19 cells as a model of human RPE, grown in normal (NG, 5.6 mM) or high glucose (HG, 25 mM), and unoxidized (UOx) or oxidized (Ox) mammalian retinal rod outer segments (OS). ARPE-19 cells were efficient at phagocytizing rod OS in both NG and HG settings. However, in HG, ARPE-19 cells treated with Ox-rod OS accumulated MDA and lipofuscins and displayed altered LC3, GRP78, and Caspase 8 expression, compared to untreated and UOx-rod OS-treated cells. Data suggest that early oxidative damage may originate from the photoreceptors and subsequently extend to the RPE, providing a new perspective to the idea that retinal degeneration depends solely on a redox alteration of the RPE.

Serine/arginine-rich splicing factors (SRSF) are a family of proteins involved in RNA metabolism, including pre-mRNA constitutive and alternative splicing. The role of SRSF proteins on mitochondria activity has already been shown for SRSF6 but SRSF4 altered expression has never been reported as disease causing. An 8-year-old patient admitted to the Hematology Unit because of leukopenia, lymphopenia, and neutropenia showed a missense variant of unknown significance on the SRSF4 gene (p.R235W) found by Whole Genome Sequencing analysis and inherited by the mother who suffered from mild leuko-neutropenia. Both patients showed lower SRSF4 protein expression compared to HD and altered mitochondrial function and energetic metabolism, which appeared associated with low mTOR phosphorylation and an imbalance in proteins regulating biogenesis (i.e., CLUH) and mitochondrial dynamics (i.e., DRP1, OPA1). Transfection with the wt-SRSF4 gene restored the mitochondrial function. In conclusion, this study shows that the de-scribed variant of the SRSF4 gene is pathogenetic and causes reduced SRSF4 protein expression, which leads to cells’ mitochondrial function impairment. Since mitochondrial function is crucial for hematopoietic stem cells maintenance and some genetic bone marrow failure syndromes display mitochondrial defects, SRSF4 mutation could have substantially contribute to the clinical phenotype of our patient.