Login to Access Video or Poster Abstract: MP19-07
Sources of Funding: NIH NIDDK P20DK100863 (MLS); R21 DK109912 (SPH, MLS); NIH NIDCR R01DE022032 (SPH)

Introduction

Randall&[prime]s plaques at the renal papillary tips are known sites of stone propagation, yet the inciting events leading to Randall&[prime]s plaque are poorly understood. Noncollagneous proteins (NCPs) including osteopontin have been identified in the sites of biomineralization and may be critical in the early formation of Randall&[prime]s plaques. In contrast to traditional bright-field and polarized microscopy, fluorescence microscopy has the potential to localize and map these proteinaceous regions. This study was undertaken to localize osteogenic noncollagenous proteins in renal papilla as a potential nidus toward stone pathogenesis.

Methods

Whole human renal papillae including tissue proximal to the fornix with grossly visible Randall&[prime]s plaque were harvested en bloc after nephrectomy. Papillary tissues were processed in a routine fashion and longitudinal histologic sections were characterized using bright field (BF), polarized light (PM), fluorescence (FM), and scanning electron microscopy (SEM) techniques (see Figure) before and after decalcification using EDTA solution. Immunolocalization of NCPs including osteopontin was performed via immunogold labeling of ultrathin sections.

Results

Mineralized tubules (average diameter 18µm) revealed strong auto-fluorescence in blue, green, and red spectra. After decalcification of the same sections, birefringence visible under polarized light (PM) microscopy disappeared. However, the auto-fluorescence potentially associated with NCPs remained intact. Correlative light and electron microscopy (CLEM) and ultrastructural analyses revealed the mineralized tubular structure in renal papilla is rich in osteopontin (gold particles in Figure).

Conclusions

Localization of precursors to Randall&[prime]s plaque was detected by auto-fluorescence. NCPs appear to closely associate with tubules of diameter of 18 µm consistent with vascular elements in renal papilla, and may be intimately associated with stone formation.

Funding

NIH NIDDK P20DK100863 (MLS); R21 DK109912 (SPH, MLS); NIH NIDCR R01DE022032 (SPH)