Human SLC4A11-C functions as a DIDS-stimulatable H+ (OH-) permeation pathway: partial correction of R109H mutant transport

The SLC4A11 gene mutations cause a variety of genetic corneal diseases, including congenital hereditary endothelial dystrophy 2 (CHED2), Harboyan syndrome, some cases of Fuchs' endothelial dystrophy (FECD), and possibly familial keratoconus. Three NH2-terminal variants of the human SLC4A11 gene, named SLC4A11-A, -B, and -C are known. The SLC4A11-B variant has been the focus of previous studies. Both the expression of the SLC4A11-C variant in the cornea and its functional properties have not been characterized, and therefore its potential pathophysiological role in corneal diseases remains to be explored. In the present study, we demonstrate that SLC4A11-C is the predominant SLC4A11 variant expressed in human corneal endothelial mRNA and that the transporter functions as an electrogenic H+ (OH-) permeation pathway. Disulfonic stilbenes, including 4,4'-diisothiocyano2,2'-stilbenedisulfonate (DIDS), 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonate (H2DIDS), and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonate (SITS), which are known to bind covalently, increased SLC4A11-C-mediated H+ (OH-) flux by 150-200% without having a significant effect in mock-transfected cells. Noncovalently interacting 4,4'-diaminostilbene-2,2'-disulfonate (DADS) was without effect. We tested the efficacy of DIDS on the functionally impaired R109H mutant (SLC4A11-C numbering) that causes CHED2. DIDS (1 mM) increased H+ (OH-) flux through the mutant transporter by similar to 40-90%. These studies provide a basis for future testing of more specific chemically modified dilsulfonic stilbenes as potential therapeutic agents to improve the functional impairment of specific SLC4A11 mutant transporters.