Here, we present kidney tissues from dRTA-affected siblings heterozygous for kAE1G609R, characterized by predominant absence rather than mistargeting of kAE1 in intercalated cells.
Our data unveil the molecular mechanism of Golgi retention of kAE1G701D and suggest that disruption of the COPI-kAE1G701D interaction could be a therapeutic strategy to treat dRTA caused by this mutant.
The promoter regions of the kAE1 gene with the minor allele A at rs999716 downstream of the TATA box showed reduced promoter activities compared that with the major allele G. Patients with the A allele at rs999716 may express less kAE1 mRNA and protein in the intercalated cells, developing incomplete dRTA.
Thus impaired trafficking of the kAE1G701D and A858D mutants would lead to a profound decrease in functional kAE1 at the basolateral membrane of alpha-intercalated cells in the distal nephron of the patients with dRTA.
Therefore, compound heterozygous patients expressing both recessive mutants (G701D/S773P) likely developed dRTA due to the lack of a functional kAE1 at the basolateral surface of alpha-intercalated cells.
Individuals heterozygous with wild-type (WT) kAE1 either did not display any symptoms of dRTA (DeltaV850/WT) or displayed a mild incomplete form of dRTA (A858D/WT), while compound heterozygotes (DeltaV850/A858D) had dRTA.
Heterozygotes with SAO are able to acidify their urine, without symptoms of dRTA (distal renal tubular acidosis) that can be associated with mutations in kAE1.
The biosynthesis and trafficking of kAE1 containing a novel recessive missense dRTA mutation (kAE1S773P) was studied in transiently transfected HEK-293 cells, expressing the mutant alone or in combination with wild-type kAE1 or another recessive mutant, kAE1G701D.
Intracellular retention of kAE1 in the alpha-intercalated cells of the kidney would account for the impaired acid secretion into the urine characteristic of dRTA.