Modulation of Tmem135 Leads to Retinal Pigmented Epithelium Pathologies in Mice

Abstract

Purpose Aging is a critical risk factor for the development of retinal diseases, but how aging perturbs ocular homeostasis and contributes to disease is unknown. We identified transmembrane protein 135 ( Tmem135 ) as a gene important for regulating retinal aging and mitochondrial dynamics in mice. Overexpression of Tmem135 causes mitochondrial fragmentation and pathologies in the hearts of mice. In this study, we examine the eyes of mice overexpressing wild-type Tmem135 ( Tmem135 TG) and compare their phenotype to Tmem135 mutant mice. Methods Eyes were collected for histology, immunohistochemistry, electron microscopy, quantitative PCR, and Western blot analysis. Before tissue collection, electroretinography (ERG) was performed to assess visual function. Mouse retinal pigmented epithelium (RPE) cultures were established to visualize mitochondria. Results Pathologies were observed only in the RPE of Tmem135 TG mice , including degeneration, migratory cells, vacuolization, dysmorphogenesis, cell enlargement, and basal laminar deposit formation despite similar augmented levels of Tmem135 in the eyecup (RPE/choroid/sclera) and neural retina. We observed reduced mitochondria number and size in the Tmem135 TG RPE. ERG amplitudes were decreased in 365-day-old mice overexpressing Tmem135 that correlated with reduced expression of RPE cell markers. In Tmem135 mutant mice, RPE cells are thicker, smaller, and denser than their littermate controls without any signs of degeneration. Conclusions Overexpression and mutation of Tmem135 cause contrasting RPE abnormalities in mice that correlate with changes in mitochondrial shape and size (overfragmented in TG vs. overfused in mutant). We conclude proper regulation of mitochondrial homeostasis by TMEM135 is critical for RPE health.

The Influence of Mitochondrial Dynamics and Function on Retinal Ganglion Cell Susceptibility in Optic Nerve Disease

“…Similar observations were also made in vivo. Enlarged mitochondria were observed in the RPE and photoreceptor cells of Tmem135 mutants [ 162 ], while significantly smaller mitochondria were found in the RPE [ 163 ] as well as the hearts [ 164 ] of mice over-expressing Tmem135 . Mitochondrial energy production may be also affected in these mice since mitochondrial oxidative phosphorylation proteins were increased in the retinas and hearts of Tmem135 mutants while their decrease was observed in the same tissues of the over-expressors [ 163 ].…”

“…Enlarged mitochondria were observed in the RPE and photoreceptor cells of Tmem135 mutants [ 162 ], while significantly smaller mitochondria were found in the RPE [ 163 ] as well as the hearts [ 164 ] of mice over-expressing Tmem135 . Mitochondrial energy production may be also affected in these mice since mitochondrial oxidative phosphorylation proteins were increased in the retinas and hearts of Tmem135 mutants while their decrease was observed in the same tissues of the over-expressors [ 163 ]. Evaluation of mitochondrial sizes in the axons of the myelinated optic nerve showed that mutant mice exhibited impaired fission leading to significantly larger mitochondria, while over-expressing transgenic animals trended toward smaller mitochondria compared to WT littermates ( Figure 7 ).…”

TMEM135 is a Novel Regulator of Mitochondrial Dynamics and Physiology with Implications for Human Health Conditions

“…It should also be noted that Ca 2+ regulates several cellular processes, including apoptosis, signal transduction, and transcriptional regulation [ 79 , 80 , 81 ]. Given TMEM135 is involved in mitochondrial dynamics [ 12 , 82 , 83 ], we speculate that TMEM135 may also regulate Ca 2+ flux, Ca 2+ uptake, and Ca 2+ -dependent transcription factors and kinases. TMEM135 may regulate several transcription factors that have integral roles in maintaining Ca 2+ dynamics in the cell.…”

A mutation in transmembrane protein 135 impairs lipid metabolism in mouse eyecups

“…Previous studies also suggested the function of TMEM135 in lipid metabolism 5 , 6 . In addition, a study using transgenic mice overexpressing the Tmem135 gene ( Tmem135 TG) showed that Tmem135 overexpression results in RPE dysmorphogenesis and degeneration 7 . Electron micrographs of the RPE from Tmem135 FUN025/FUN025 mice showed over-fused (elongated) mitochondrial networks while the RPE of Tmem135 TG mice displayed over-fragmented mitochondrial networks relative to controls 3 , 7 .…”

“…In addition, a study using transgenic mice overexpressing the Tmem135 gene ( Tmem135 TG) showed that Tmem135 overexpression results in RPE dysmorphogenesis and degeneration 7 . Electron micrographs of the RPE from Tmem135 FUN025/FUN025 mice showed over-fused (elongated) mitochondrial networks while the RPE of Tmem135 TG mice displayed over-fragmented mitochondrial networks relative to controls 3 , 7 . Despite their morphological differences, both Tmem135 FUN025/FUN025 and Tmem135 TG RPE show reduced mitochondrial function 8 .…”