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.