Tissue Inhibitor of Metalloproteinase 3 (TIMP3) mutations increase glycolytic activity and dysregulate glutamine metabolism in RPE cells.

OBJECTIVES: Mutations in Tissue Inhibitor of Metalloproteinases 3 (TIMP3) cause Sorsby's Fundus Dystrophy (SFD), a dominantly inherited, rare form of macular degeneration that results in vision loss. TIMP3 is synthesized primarily by retinal pigment epithelial (RPE) cells, which constitute the outer blood-retinal barrier. One major function of RPE is the synthesis and transport of vital nutrients, such as glucose, to the retina. Recently, metabolic dysfunction in RPE cells has emerged as an important contributing factor in retinal degenerations. We set out to determine if RPE metabolic dysfunction was contributing to SFD pathogenesis. METHODS: Quantitative proteomics was conducted on RPE of mice expressing the S179C variant of TIMP3, known to be causative of SFD in humans. Proteins found to be differentially expressed (P < 0.05) were analyzed using statistical overrepresentation analysis to determine enriched pathways, processes, and protein classes using g:profiler and PANTHER Gene Ontology. We examined the effects of mutant TIMP3 on RPE metabolism using human ARPE-19 cells expressing mutant S179C TIMP3 and patient-derived induced pluripotent stem cell-derived RPE (iRPE) carrying the S204C TIMP3 mutation. RPE metabolism was directly probed using isotopic tracing coupled with GC/MS analysis. Steady state [U-13C6] glucose isotopic tracing was preliminarily conducted on S179C ARPE-19 followed by [U-13C6] glucose and [U-13C5] glutamine isotopic tracing in SFD iRPE cells. RESULTS: Quantitative proteomics and enrichment analysis conducted on RPE of mice expressing mutant S179C TIMP3 identified differentially expressed proteins that were enriched for metabolism-related pathways and processes. Notably these results highlighted dysregulated glycolysis and glucose metabolism. Stable isotope tracing experiments with [U-13C6] glucose demonstrated enhanced glucose utilization and glycolytic activity in S179C TIMP3 APRE-19 cells. Similarly, [U-13C6] glucose tracing in SFD iRPE revealed increased glucose contribution to glycolysis and the TCA cycle. Additionally, [U-13C5] glutamine tracing found evidence of altered malic enzyme activity. CONCLUSIONS: This study provides important information on the dysregulation of RPE glucose metabolism in SFD and implicates a potential commonality with other retinal degenerative diseases, emphasizing RPE cellular metabolism as a therapeutic target.

Derivation of Clinical-Grade Induced Pluripotent Stem Cell Lines from Erythroid Progenitor Cells in Xenofree Conditions.

One of the major hurdles in realizing the therapeutic potential of human-induced pluripotent stem cells (iPSC) is the generation of clinical-grade iPSC lines and their differentiated progenies for preclinical and clinical applications. Therefore, there is a need to have standardized protocols for efficient generation of clinical-grade iPSC lines from easily accessible somatic cells in feeder-free, xenofree GMP grade culture conditions without genomic integration of the reprogramming factors. Here, we provide a detailed protocol for expansion of erythroid progenitor cells from peripheral blood mononuclear cells (PBMNC) and generation of iPSC lines in feeder-free and xenofree culture conditions from these cells by using GMP grade reagents. With this optimized protocol, clinical-grade iPSC lines can be derived from erythroid progenitor cells expanded from peripheral blood, which is easy-to-access, minimally invasive, and can be obtained from any donors. It will have implications in developing a large number of iPSC lines from individual healthy donors, diseased patients, or donors with homozygous human leukocyte antigen (HLA) for "haplobanking."

3D iPSC modeling of the retinal pigment epithelium-choriocapillaris complex identifies factors involved in the pathology of macular degeneration.

The retinal pigment epithelium (RPE)-choriocapillaris (CC) complex in the eye is compromised in age-related macular degeneration (AMD) and related macular dystrophies (MDs), yet in vitro models of RPE-CC complex that enable investigation of AMD/MD pathophysiology are lacking. By incorporating iPSC-derived cells into a hydrogel-based extracellular matrix, we developed a 3D RPE-CC model that recapitulates key features of both healthy and AMD/MD eyes and provides modular control over RPE and CC layers. Using this 3D RPE-CC model, we demonstrated that both RPE- and mesenchyme-secreted factors are necessary for the formation of fenestrated CC-like vasculature. Our data show that choroidal neovascularization (CNV) and CC atrophy occur in the absence of endothelial cell dysfunction and are not necessarily secondary to drusen deposits underneath RPE cells, and CC atrophy and/or CNV can be initiated systemically by patient serum or locally by mutant RPE-secreted factors. Finally, we identify FGF2 and matrix metalloproteinases as potential therapeutic targets for AMD/MDs.

Generation of an integration-free iPSC line (CSCRi005-A) from erythroid progenitor cells of a healthy Indian male individual.

Reprogramming of somatic cells with higher genome integrity, and use of non-integrating gene delivery methods and xeno-free cell culture conditions aid in the generation of iPSCs which are more suitable for disease modelling and clinical applications. We describe here an iPSC line generated using such conditions, which expressed all the pluripotency markers, retained normal karyotype and exhibited the potential for tri-lineage differentiation, both in-vitro and in-vivo. This is the first iPSC line available from a healthy Indian individual for researchers.

Understanding the Molecular Basis of Heterogeneity in Induced Pluripotent Stem Cells.

Reprogramming of somatic cells to generate induced pluripotent stem cells (iPSCs) has considerable latency and generates epigenetically distinct partially and fully reprogrammed clones. To understand the molecular basis of reprogramming and to distinguish the partially reprogrammed iPSC clones (pre-iPSCs), we analyzed several of these clones for their molecular signatures. Using a combination of markers that are expressed at different stages of reprogramming, we found that the partially reprogrammed stable clones have significant morphological and molecular heterogeneity in their response to transition to the fully pluripotent state. The pre-iPSCs had significant levels of OCT4 expression but exhibited variable levels of mesenchymal-to-epithelial transition. These novel molecular signatures that we identified would help in using these cells to understand the molecular mechanisms in the late of stages of reprogramming. Although morphologically similar mouse iPSC clones showed significant heterogeneity, the human iPSC clones isolated initially on the basis of morphology were highly homogeneous with respect to the levels of pluripotency.