Inflammation-induced osteogenic signaling promotes calcium phosphate crystal formation in kidneys via MAPK, NF-κB,...

Approximately two-thirds of patients with kidney stones exhibit Randall's plaques, interstitial calcium phosphate deposits extending to the papillary surface, serving as stone formation niduses. Although inflammation and osteogenic processes have been implicated in plaque development, their mechanistic connection remains unclear. In vascular calcification, which shares key pathological features with Randall's plaques, pro-inflammatory cytokines upregulate osteogenesis-related proteins to promote calcification. Whether similar signaling occurs in kidneys remains unclear. This study aimed to explore physiopathology and facilitate the development of potential targeted therapies for kidney stones.

HK-2 cells were treated with calcium and pro-inflammatory cytokines to assess calcium deposition and investigate osteogenic transition signaling pathways. Non-cell-based assays were developed to examine the direct effects of osteogenesis-related proteins on specific stages of calcium phosphate crystal formation, including nucleation, growth, and aggregation. To determine whether inflammation is related to osteogenic responses and calcification in vivo, a novel rat model of renal calcium deposition was established by combining a high-calcium diet with unilateral ureteral obstruction surgery. Renal calcium deposits were also evaluated.

In vitro, pro-inflammatory cytokines enhanced calcium-induced mineralization in renal tubular cells and were associated with the activation of MAPK, NF-κB, and Smad signaling pathways, along with the upregulation of osteogenesis-related proteins. These proteins exerted direct, stage-specific effects on calcium phosphate crystal nucleation, growth, and aggregation. In our novel rat model, inflammation enhanced renal calcium deposition and upregulated osteogenic markers within 1 month. The positive correlation between the renal expression of inflammatory cytokines and osteoblast markers mirrored the in vitro findings.

This study provides insight into renal calcification, suggesting that pro-inflammatory cytokines are associated with activation of MAPK, NF-κB, and Smad signaling pathways and upregulation of osteogenesis-related proteins, which may contribute to key stages of crystal formation. Furthermore, this work establishes a novel and time-efficient animal model that offers a valuable platform for investigating the pathogenesis of renal calcification, including processes potentially relevant to Randall's plaque-associated calcification.