Dnajb11-Kidney Disease Develops from Reduced Polycystin-1 Dosage but not Unfolded Protein Response in Mice

Abstract

Background: Patients with heterozygous inactivating mutations in DNAJB11 manifest with cystic but not enlarged kidneys and renal failure in adulthood. Pathogenesis is proposed to resemble an overlap of autosomal dominant polycystic kidney disease (ADPKD) and autosomal dominant tubulointerstitial kidney disease (ADTKD), but this phenotype has never been modeled in vivo. DNAJB11 encodes an Hsp40 co-chaperone in the endoplasmic reticulum (ER): the site of maturation of the ADPKD polycystin-1 (PC1) protein, and of unfolded protein response (UPR) activation in ADTKD. We hypothesized that investigation of DNAJB11 would shed light on mechanisms for both diseases. Methods: We used germline and conditional alleles to model Dnajb11-kidney disease in mice. In complementary experiments we generated two novel Dnajb11 -/- cell lines that allow assessment of Polycystin-1 (PC1) C-terminal fragment and its ratio to the immature full-length protein. Results: Dnajb11 loss results in a profound defect in PC1 cleavage but with no effect on other cystoproteins assayed. Dnajb11 -/- mice are live-born at below the expected Mendelian ratio and die at weaning age with cystic kidneys. Conditional loss of Dnajb11 in renal tubular epithelium results in PC1 dosage-dependent kidney cysts, thus defining a shared mechanism with ADPKD. Dnajb11 mice show no evidence of UPR activation nor cyst-independent fibrosis, which is a fundamental distinction from typical ADTKD pathogenesis. Conclusions: DNAJB11-kidney disease is on the spectrum of ADPKD phenotypes with a Polycystin-1-dependent pathomechanism. The absence of UPR across multiple models suggests that alternative mechanisms, which may be cyst-dependent, explain the renal failure in the absence of kidney enlargement.

The Role of the Co-Chaperone DNAJB11 in Polycystic Kidney Disease: Molecular Mechanisms and Cellular Origin of Cyst Formation

“…does not result in cystic kidneys suggests that cysts are not derived from distal tubular segments where Ksp-Cre is expressed (thick ascending loop of Henle, distal tubule, and collecting duct). A recent study also reported the absence of cysts in Ksp-Cre; Dnajb11 fl/fl mice (42). It was shown in this study that a reduction in Pkd1 copy number (Pkd1 +/-) in these animals resulted in cyst formation (42).…”

“…A recent study also reported the absence of cysts in Ksp-Cre; Dnajb11 fl/fl mice (42). It was shown in this study that a reduction in Pkd1 copy number (Pkd1 +/-) in these animals resulted in cyst formation (42). Since patients with ADPKD caused by monoallelic DNAJB11 mutations do not have heterozygous PKD1 mutations it was speculated that a lower basal PC1 dosage in humans compared to mice may explain cyst formation in the human disease (42).…”

“…It was shown in this study that a reduction in Pkd1 copy number (Pkd1 +/-) in these animals resulted in cyst formation (42). Since patients with ADPKD caused by monoallelic DNAJB11 mutations do not have heterozygous PKD1 mutations it was speculated that a lower basal PC1 dosage in humans compared to mice may explain cyst formation in the human disease (42). Our finding that cysts in Dnajb11-deficient mice are derived from proximal tubules but not from distal tubule segments provides a simple explanation for cyst formation without the requirement of additional factors or genetic manipulations.…”

“…Future studies in human samples from patients with cystic disease caused by monoallelic DNAJB11 mutations will have to test whether cyst epithelia indeed harbor somatic mutations as reported for PKD1 or PKD2 (20). As shown recently, cyst burden and kidney enlargement in Dnajb11-deficient mice are much milder than in Pkd1or Pkd2-deficient mouse models (42). This corresponds with the human disease, which is also characterized by a milder cystic phenotype and slower disease progression compared to classical ADPKD (18).…”

Inhibition of Asparagine Synthetase Effectively Retards Polycystic Kidney Disease Progression

“…Notably, we found that ATF4 is upregulated in all PKD models described above, including KspCre;Pkd1 ΔC/flox kidneys at P4 ( Fig 3B ) and P45-tamoxifen-induced Tam-Cre;Pkd1 ΔC/flox kidneys at P160 ( Fig 3C ). Of interest, the ATF4-ASNS axis is known to be activated in response to ER stress by PERK-dependent activation of unfolded protein response (UPR), a pathway that has been shown not to be de-regulated in PKD (Fedeles et al , 2015; Roy et al , 2023), but also during an imbalance in amino acids availability in cells and tissues via activation of the General Control Nonderepressible-2- kinase (GCN2) within the so called amino acid response (AAR) that converges downstream with the PERK pathway on eIF2alpha which translationally regulates ATF4 levels (Lomelino et al , 2017) ( Fig 3A ). This process is mimicked by the limitation of essential amino acids (EAAs) in cell culture (Jin et al , 2021), whereby GCN2 acts as a metabolic sensor for the depletion of amino acids, via the binding of uncharged tRNAs (Kanno et al , 2020).…”