No abstract

Stem cell scientists have developed methods for the self-formation of artificial organs, often referred to as organoids. Organoids can be used as model systems for research in multiple biological disciplines. Yoshiki Sasai’s innovation for deriving mammalian retinal tissue from in vitro stem cells has had a large impact on the study of the biology of vision. New developments in retinal organoid technology provide avenues for in vitro models of human retinal diseases, studies of pathological mechanisms, and development of therapies for retinal degeneration, including electronic retinal implants and gene therapy. Moreover, these innovations have played key roles in establishing models for large-scale drug screening, studying the stages of retinal development, and providing a human model for personalized therapeutic approaches, like cell transplants to replace degenerated retinal cells. Here, we first discuss the importance of human retinal organoids to the biomedical sciences. Then, we review various functional features of retinal organoids that have been developed. Finally, we highlight the current limitations of retinal organoid technologies.

The tyrosine kinase Janus kinase 3 (JAK3) contributes to signaling regulating the proliferation and apoptosis of lymphocytes and tumor cells. Replacement of lysine by alanine in the catalytic subunit yields the inactive (K851A)JAK3 mutant that underlies severe combined immune deficiency. The gain-of-function mutation (A572V)JAK3 is found in acute megakaryoplastic leukemia and T cell lymphoma. The excessive nutrient demand of tumor cells requires upregulation of transporters in the cell membrane including peptide transporters PEPT1 and PEPT2. The carriers further accomplish intestinal peptide transport. Little is known about signaling regulating peptide transport. The present study explored whether PEPT1 and PEPT2 are upregulated by JAK3. PEPT1 or PEPT2 was expressed in Xenopus oocytes with or without additional expression of JAK3, and electrogenic peptide (glycine-glycine) transport was determined by dual-electrode voltage clamp. PEPT2-HA membrane protein abundance was analyzed by chemiluminescence. Intestinal electrogenic peptide transport was estimated from peptide-induced current in Ussing chamber experiments. In PEPT1- and PEPT2-expressing oocytes, but not in water-injected oocytes, the dipeptide gly-gly generated an inward current, which was significantly increased following coexpression of JAK3. The effect of JAK3 on PEPT1 was mimicked by (A568V)JAK3 but not by (K851A)JAK3. JAK3 increased maximal peptide-induced current in PEPT1-expressing oocytes but rather decreased apparent affinity of the carrier. Coexpression of JAK3 enhanced the PEPT2-HA protein abundance in the cell membrane. In JAK3- and PEPT1-expressing oocytes, peptide-induced current was blunted by the JAK3 inhibitor WHI-P154, 4-[(3'-bromo-4'-hydroxyphenyl)amino]-6,7-dimethoxyquinazoline (22 μM). In intestinal segments gly-gly generated a current which was significantly smaller in JAK3-deficient mice (jak3⁻/⁻) than in wild-type mice (jak3⁺/⁺). In conclusion, JAK3 is a powerful regulator of peptide transporters PEPT1 and PEPT2.

Loss of function mutations of the chorein-encoding gene VPS13A lead to chorea-acanthocytosis (ChAc), a neurodegenerative disorder with accelerated suicidal neuronal cell death, which could be reversed by lithium. Chorein upregulates the serum and glucocorticoid inducible kinase SGK1. Targets of SGK1 include the Na + /K +-ATPase, a pump required for cell survival. To explore whether chorein-deficiency affects na + /K + pump capacity, cortical neurons were differentiated from iPSCs generated from fibroblasts of ChAc patients and healthy volunteers. Na + /K + pump capacity was estimated from K +-induced whole cell outward current (pump capacity). As a result, the pump capacity was completely abolished in the presence of Na + /K + pump-inhibitor ouabain (100 µM), was significantly smaller in ChAc neurons than in control neurons, and was significantly increased in ChAc neurons by lithium treatment (24 hours 2 mM). The effect of lithium was reversed by SGK1-inhibitor GSK650394 (24 h 10 µM). Transmembrane potential (V m) was significantly less negative in ChAc neurons than in control neurons, and was significantly increased in ChAc neurons by lithium treatment (2 mM, 24 hours). The effect of lithium on V m was virtually abrogated by ouabain. Na + /K + α1-subunit transcript levels and protein abundance were significantly lower in ChAc neurons than in control neurons, an effect reversed by lithium treatment (2 mM, 24 hours). In conclusion, consequences of chorein deficiency in ChAc include impaired Na + /K + pump capacity. The widely expressed 1-3 phosphatidylinositol lipid binding protein 4 chorein up-regulates phosphoinositide-3-kinase signalling and participates in the regulation of diverse cellular functions. Chorein-sensitive functions include actin polymerization and cell stiffness 2,3,5,6 , degranulation 3,5 , autophagy and cell survival 4,7-12. Chorea-acanthocytosis (ChAc) is a rare hereditary disease caused by loss-of-function-mutations of the chorein encoding gene VPS13A (vacuolar protein sorting-associated protein 13A) 7,13 , leading to progressive autosomal recessive neurodegenerative disease characterized by severe pleotropic movement disorders, epilepsy, decline of cognitive functions, and variable erythrocyte acanthocytosis 4,7,11,14-22. Eventually the neurodegeneration results in severe disability and early death 16 .