Determination of urinary lithogenic parameters in murine models orthologous to autosomal dominant polycystic kidney disease

Assessment of metabolic risk factors for nephrolithiasis in patients with autosomal dominant polycystic kidney disease: a cross-sectional study

BACKGROUND

Nephrolithiasis is more common in autosomal dominant polycystic kidney disease (ADPKD) than in the normal population. We aimed to investigate the anatomical and metabolic factors that may be associated with nephrolithiasis in patients with ADPKD METHODS: In this cross-sectional study, a total of 180 participants were included. Eighty-five patients with ADPKD [42 patients with nephrolithiasis (PKD N +) and 43 without nephrolithiasis (PKD N -)] were recruited. Forty-seven nephrolithiasis patients without ADPKD (N) and 48 healthy controls (HC) were selected as control groups. 24-h urine collections were measured in all participants. 24-h urine citrate, calcium, urate, oxalate, magnesium and sodium, serum electrolytes, and eGFRs were compared.

RESULTS

Total kidney volumes were not different between patients with PKD N + and PKD N -. Hypocitraturia was common in all patients with ADPKD (69.4%), and it was not different between PKD N + (76.2%) and PKD N- (62.8%). However, hypocitraturia was statistically higher in PKD N + and PKD N - than in N (38.3%) and HC (12.5%) (p<0.05). 24-h urine calcium, urate, and oxalate levels were similar between PKD N + and PKD N - CONCLUSIONS: Hypocitraturia was found to be significantly higher in patients with ADPKD than in healthy adults and other kidney stone patients.

Crystal deposition triggers tubule dilation that accelerates cystogenesis in polycystic kidney disease

The rate of disease progression in autosomal-dominant (AD) polycystic kidney disease (PKD) exhibits high intra-familial variability suggesting that environmental factors may play a role. We hypothesized that a prevalent form of renal insult may accelerate cystic progression and investigated tubular crystal deposition. We report that calcium oxalate (CaOx) crystal deposition led to rapid tubule dilation, activation of PKD-associated signaling pathways, and hypertrophy in tubule segments along the affected nephrons. Blocking mTOR signaling blunted this response and inhibited efficient excretion of lodged crystals. This mechanism of "flushing out" crystals by purposefully dilating renal tubules has not previously been recognized. Challenging PKD rat models with CaOx crystal deposition, or inducing calcium phosphate deposition by increasing dietary phosphorous intake, led to increased cystogenesis and disease progression. In a cohort of ADPKD patients, lower levels of urinary excretion of citrate, an endogenous inhibitor of calcium crystal formation, correlated with increased disease severity. These results suggest that PKD progression may be accelerated by commonly occurring renal crystal deposition which could be therapeutically controlled by relatively simple measures.

Polycystin-1 dysfunction impairs electrolyte and water handling in a renal precystic mouse model for ADPKD

The PKD1 gene encodes polycystin-1 (PC1), a mechanosensor triggering intracellular responses upon urinary flow sensing in kidney tubular cells. Mutations in PKD1 lead to autosomal dominant polycystic kidney disease (ADPKD). The involvement of PC1 in renal electrolyte handling remains unknown since renal electrolyte physiology in ADPKD patients has only been characterized in cystic ADPKD. We thus studied the renal electrolyte handling in inducible kidney-specific Pkd1 knockout (iKsp- Pkd1^-/-) mice manifesting a precystic phenotype. Serum and urinary electrolyte determinations indicated that iKsp- Pkd1^-/- mice display reduced serum levels of magnesium (Mg²⁺), calcium (Ca²⁺), sodium (Na⁺), and phosphate (P_i) compared with control ( Pkd1^+/+) mice and renal Mg²⁺, Ca²⁺, and P_i wasting. In agreement with these electrolyte disturbances, downregulation of key genes for electrolyte reabsorption in the thick ascending limb of Henle's loop (TA;, Cldn16, Kcnj1, and Slc12a1), distal convoluted tubule (DCT; Trpm6 and Slc12a3) and connecting tubule (CNT; Calb1, Slc8a1, and Atp2b4) was observed in kidneys of iKsp- Pkd1^-/- mice compared with controls. Similarly, decreased renal gene expression of markers for TAL ( Umod) and DCT ( Pvalb) was observed in iKsp- Pkd1^-/- mice. Conversely, mRNA expression levels in kidney of genes encoding solute and water transporters in the proximal tubule ( Abcg2 and Slc34a1) and collecting duct ( Aqp2, Scnn1a, and Scnn1b) remained comparable between control and iKsp- Pkd1^-/- mice, although a water reabsorption defect was observed in iKsp- Pkd1^-/- mice. In conclusion, our data indicate that PC1 is involved in renal Mg²⁺, Ca²⁺, and water handling and its dysfunction, resulting in a systemic electrolyte imbalance characterized by low serum electrolyte concentrations.

The genetic framework for development of nephrolithiasis

Over 1%–15% of the population worldwide is affected by nephrolithiasis, which remains the most common and costly disease that urologists manage today. Identification of at-risk individuals remains a theoretical and technological challenge. The search for monogenic causes of stone disease has been largely unfruitful and a technological challenge; however, several candidate genes have been implicated in the development of nephrolithiasis. In this review, we will review current data on the genetic inheritance of stone disease, as well as investigate the evolving role of genetic analysis and counseling in the management of nephrolithiasis.