Hydrogen Sulfide Deficiency Contributes to Tubular Damage and Calcium Oxalate Crystal Formation in Hyperoxaluria Nephropathy: Role of Osteopontin and Tamm-Horsfall Protein.

Hydrogen sulfide (H2S) exerts regulatory functions in kidney diseases. However, its protective role against kidney stone formation remains unclear. Here, we demonstrate that hyperoxaluria or oxalate exposure impairs H2S formation, leading to tubular injury and calcium oxalate (CaOx) crystal deposition in both in vivo and in vitro models. In male rats fed 5% hydroxy-L-proline (HP), time-dependent increases in urinary supersaturation, tubular damage, and renal CaOx deposition were observed compared to controls. These changes were associated with the decreased expression of H2S-producing enzymes and elevated urinary secretion of osteopontin (OPN) and Tamm-Horsfall protein (THP). Notably, the protein level and activity of specificity protein 1 (Sp1), a transcription factor regulating these enzymes, were markedly decreased in HP-treated kidneys. Chronic supplementation with the H2S donor GYY4137 (GYY) significantly attenuated HP-induced tubular injury and CaOx deposition by reducing OPN and THP secretion. Consistent with in vivo results, H2S donors mitigated oxalate-induced tubular cell damage and CaOx formation in MDCK cells. Mechanistically, oxalate activated cyclic AMP/protein kinase A (PKA) signaling, which promoted OPN and THP secretion; these effects were eradicated by the PKA inhibitor H89 or GYY. These findings indicate that hyperoxaluria impairs Sp1 transcriptional activity, resulting in H2S deficiency and compromised anticrystallization defense in oxalate-induced tubulopathy.