To elucidate the molecular events in solute carrier family 4 member 11 (SLC4A11)-deficient corneal endothelium that lead to the endothelial dysfunction that characterizes the dystrophies associated with SLC4A11 mutations, congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy 4. METHODS. Comparative transcriptomic analysis (CTA) was performed in primary human corneal endothelial cells (pHCEnC) and murine corneal endothelial cells (MCEnC) with normal and reduced levels of SLC4A11 (SLC4A11 KD pHCEnC) and Slc4a11 (Slc4a11 −/− MCEnC), respectively. Validation of differentially expressed genes was performed using immunofluorescence staining of CHED corneal endothelium, as well as western blot and quantitative PCR analysis of SLC4A11 KD pHCEnC and Slc4a11 −/− MCEnC. Functional analyses were performed to investigate potential functional changes associated with the observed transcriptomic alterations. RESULTS. CTA revealed inhibition of cell metabolism and ion transport function as well as mitochondrial dysfunction, leading to reduced adenosine triphosphate (ATP) production, in SLC4A11 KD pHCEnC and Slc4a11 −/− MCEnC. Co-localization of SNARE protein STX17 with mitochondria marker COX4 was observed in CHED corneal endothelium, as was activation of AMPK-p53/ULK1 in both SLC4A11 KD pHCEnC and Slc4a11 −/− MCEnC, providing additional evidence of mitochondrial dysfunction and mitophagy. Reduced Na +-dependent HCO 3 − transport activity and altered NH 4 Cl-induced membrane potential changes were observed in Slc4a11 −/− MCEnC. CONCLUSIONS. Reduced steady-state ATP levels and subsequent activation of the AMPK-p53 pathway provide a link between the metabolic functional deficit and transcriptome alterations, as well as evidence of insufficient ATP to maintain the Na + /K +-ATPase corneal endothelial pump as the cause of the edema that characterizes SLC4A11associated corneal endothelial dystrophies.
Mutations in the solute-linked carrier family 4 member 11 (SLC4A11) gene are associated with congenital hereditary endothelial dystrophy (CHED), Fuchs endothelial corneal dystrophy and Harboyan syndrome, in all of which visually significant cornea edema may require corneal transplantation. However, the pathogenesis of SLC4A11-associated corneal endothelial dystrophies remains to be elucidated. Recent evidence suggested cellular respiration reprogramming and mitochondrial oxidative stress in SLC4A11-deficient corneal endothelium. Given the complexity of cellular metabolic regulation and its cell type specific impact on cellular physiology, we systemically analyzed the transcriptome of SLC4A11 knock-down primary human corneal endothelium (SLC4A11 KD pHCEnC) and corneal endothelial cells derived from Slc4a11 -/mice (Slc4a11 -/-MCEnC) to provide a comprehensive characterization of the transcriptome profile changes resulting from loss of SLC4A11. To identify the conserved molecular mechanisms that lead to cornea endothelial dysfunction in both the human and murine models, we performed comparative transcriptomic analysis. Our analysis identified inhibition of cell metabolism and ion transport function as well as mitochondria dysfunction as shared between SLC4A11 KD pHCEnC and Slc4a11 -/-MCEnC. Functional analysis confirmed the absence of SLC4A11-mediated NH 4 Cl-induced membrane depolarization in Slc4a11 -/-MCEnC. Transcriptome of SLC4A11 KD pHCEnC and Slc4a11 -/-MCEnC identified downregulation of Na + -HCO 3 transporter (NBCe1, SLC4A4), a key player in corneal endothelial 'pump' function, and upregulation of Syntaxin 17 (STX17), an initiator of mitophagy. NBCe1 and STX17 were further analyzed in Slc4a11 -/-MCEnC for functional impact and in SLC4A11 KD pHCEnC and corneal endothelium from individuals with CHED for protein expression, all Zhang et al. Energy Crisis in SLC4A11-deficient Corneal Endothelium 3 showed consistent changes with transcriptome. CHED corneal endothelium also showed decreased immunostaining intensity for mitochondria markers suggesting decreased mitochondira density . In SLC4A11 KD pHCEnC and Slc4a11 -/-MCEnC, steady state ATP depletion and ATP sensing AMPK-p53 pathway activation were observed, consistent with the prediction using transcriptome data that transcriptional factor p53 were responsible for the transcriptomic changes. These findings suggest that insufficient energy fueling the corneal endothelial 'pump', as a result of metabolic inhibition and failing mitochondria, is the direct cause of clinical phenotype of corneal edema in SLC4A11-associated corneal endothelial dystrophies. Zhang et al. Energy Crisis in SLC4A11-deficient Corneal Endothelium 4
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