Energy Shortage in Human and Mouse Models ofSLC4A11-Associated Corneal Endothelial Dystrophies

Abstract

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.

Altered gene expression in slc4a11−/− mouse cornea highlights SLC4A11 roles

“…In the transcriptome analysis here, we observed gene expression alterations centered on cytoskeletal, membrane-associated, and ECM components in the mouse cornea. This work complements a recent transcriptomic analysis of cultured human CECs subjected to siRNA to reduce their SLC4A11 expression 28 and analysis of gene expression in human CEC 29 , 30 . Analysis of gene expression changes compensating for slc4a11 loss may be useful to identify molecular targets to treat FECD and CHED pathologic conditions.…”

“…SLC4A11 defects are recognized to manifest with compromised energy metabolism. In particular, strong evidence supports a role of SLC4A11 in facilitating CEC glutaminolysis in energy production 28 , 38 , 39 and suggested a role of SLC4A11 in uncoupling mitochondria to prevent oxidative damage 40 . In the present study, we identified seven expression alterations related to CEC energy metabolism (Table 3 , Suppl.…”

Inducible Slc4a11 Knockout Triggers Corneal Edema Through Perturbation of Corneal Endothelial Pump

“… 9 A comparative transcriptome analysis performed in CHED primary CE cells and a mouse corneal endothelial cell line derived from Slc4a11 KO mice indicated a generalized inhibition of metabolic and transport gene expression in KO cells. 11 Oxidative stress appears to be a root cause of these changes since quenching mitochondrial ROS, mitochondrial uncoupling of KO cells, or circumventing glutaminolysis, all of which lower ROS production, rescue KO cells, and reverse corneal edema progression. 9 …”

The H+ Transporter SLC4A11: Roles in Metabolism, Oxidative Stress and Mitochondrial Uncoupling

“…Human CHED samples are very rare. However, a recent study examined SLC4A11 localization in two CHED endothelial specimens and found that SLC4A11 was localized to the plasma membrane and did not overlap with an ER marker [ 44 ]. Thus, it appears that trafficking and localization studies are greatly influenced by expression system, and that the use of corneal endothelial tissue and/or primary cultured endothelial cells, although more challenging, would give unequivocal answers.…”

“…Using comparative transcriptome analysis of primary cultures of human corneal endothelial cells and SLC4A11 KO MCEC (mouse corneal endothelial cells), Zhang et al [ 44 ] also found inhibition of cell metabolism, ion transport (e.g., SLC4A4-NBCe1), and mitochondrial function, along with the activation of AMPK-p53/ULK1, consistent with increased mitophagy and mitochondrial dysfunction. Downregulation of the sodium bicarbonate transporter (NBCe1) was a key finding with the cultured cells, but this was not seen in KO tissue [ 51 ].…”