NHA2 promotes cyst development in an in vitro model of polycystic kidney disease

Abstract

Key pointsr Significant and selective up-regulation of the Na + /H + exchanger NHA2 (SLC9B2) was observed in cysts of patients with autosomal dominant polycystic kidney disease.r Using the MDCK cell model of cystogenesis, it was found that NHA2 increases cyst size.Silencing or pharmacological inhibition of NHA2 inhibits cyst formation in vitro.r Polycystin-1 represses NHA2 expression via Ca 2+ /NFAT signalling whereas the dominant negative membrane-anchored C-terminal fragment (PC1-MAT) increased NHA2 levels.r Drugs (caffeine, theophylline) and hormones (vasopressin, aldosterone) known to exacerbate cysts elicit NHA2 expression.r Taken together, the findings reveal NHA2 as a potential new player in salt and water homeostasis in the kidney and in the pathogenesis of polycystic kidney disease.Abstract Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2 encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively. The molecular pathways linking polycystins to cyst development in ADPKD are still unclear. Intracystic fluid secretion via ion transporters and channels plays a crucial role in cyst expansion in ADPKD. Unexpectedly, we observed significant and selective up-regulation of NHA2, a member of the SLC9B family of Na + /H + exchangers, that correlated with cyst size and disease severity in ADPKD patients. Using three-dimensional cultures of MDCK cells to model cystogenesis in vitro, we showed that ectopic expression of NHA2 is causal to increased cyst size. Induction of PC1 in MDCK cells inhibited NHA2 expression with concordant inhibition of Ca 2+ influx through store-dependent and -independent pathways, whereas reciprocal activation of Ca 2+ influx by the dominant negative membrane-anchored C-terminal tail fragment of PC1 elevated NHA2. We showed that NHA2 is a target of Ca 2+ /NFAT signalling and is transcriptionally induced by

A new coupling of an acid‐base transporter to PKD and cyst formation

“…Using a wellrecognized in vitro model of cyst formation involving the growth of MDCK hemicysts/domes in culture, they demonstrated that both the transport inhibitor phloretin and shRNA-mediated knockdown of NHA2 markedly reduced cyst size. Prasad et al (2019) present strong evidence for the involvement of NHA2 as a novel acid-base transporter in ADPKD. NHA2 expression was closely associated with well-established ADPKD mechanisms and signalling pathways (e.g.…”

“…In the current issue of The Journal of Physiology, Prasad et al (2019) have further explored the involvement of acid-base transporters in PKD. The authors report that the human NHA2 orthologue of the bacterial NhaA (NHE superfamily) is upregulated in human ADPKD, and NHA2 stimulates cyst growth in an in vitro cell model.…”

“…Using bioinformatics and an impartially designed approach, Prasad et al (2019) identified pharmacological agents such as caffeine and theophylline (methyl xanthines) that stimulated NHA2 gene expression, as well as dexamethasone and valproic acid that inhibited expression. These agents all influence intracellular Ca 2+ in agreement with the 3D-culture model data.…”

“…Further studies are essential for clarification. Prasad et al (2019) have reported exciting new results that allude to multifaceted Perspectives J Physiol 597.2 roles of acid-base transporters in PKD. In addition to moving solutes directly and contributing to reabsorption/secretion, these transporters also regulate intracellular pH, which is well known to influence cell function, signalling pathways, and proliferation -all of which are key elements of PKD.…”

Allosteric links between the hydrophilic N‐terminus and transmembrane core of human Na+/H+ antiporter NHA2

“…In 2021, Anderegg et al corroborated the NHA2 role in blood pressure regulation in mice, and identified it as critical for the maintenance of serine–threonine with‐no‐lysine kinase 4 (WNK4) levels, and thus ultimately for the activity of the Na + /Cl − co‐transporter NCC in the distal convoluted tubules of the kidney 12 . Increased NHA2 expression also promotes cyst development in an in vitro model of polycystic kidney disease 13 . In the testis, NHA2 is relevant for sperm motility and male fertility, since the deletion of NHA2 significantly reduced the percentage of motile sperm (of about 30%) and resulted in a decrease in pregnancy rate (of about 25%) in mice 14 .…”