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.

Background

The formation of supernumerary teeth is an excellent model for studying the molecular mechanisms that control stem/progenitor cell homeostasis needed to generate a renewable source of replacement cells and tissues. Although multiple growth factors and transcriptional factors have been associated with supernumerary tooth formation, the regulatory inputs of extracellular matrix in this regenerative process remains poorly understood.

Results

In this study, we present evidence that disrupting glycosaminoglycans (GAGs) in the dental epithelium of mice by inactivating FAM20B, a xylose kinase essential for GAG assembly, leads to supernumerary tooth formation in a pattern reminiscent of replacement teeth. The dental epithelial GAGs confine murine tooth number by restricting the homeostasis of Sox2(+) dental epithelial stem/progenitor cells in a non-autonomous manner. FAM20B-catalyzed GAGs regulate the cell fate of dental lamina by restricting FGFR2b signaling at the initial stage of tooth development to maintain a subtle balance between the renewal and differentiation of Sox2(+) cells. At the later cap stage, WNT signaling functions as a relay cue to facilitate the supernumerary tooth formation.

Conclusions

The novel mechanism we have characterized through which GAGs control the tooth number in mice may also be more broadly relevant for potentiating signaling interactions in other tissues during development and tissue homeostasis.