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M2 Macrophages Attenuate AQP2+ Collecting Duct Cell Apoptosis via the TRAF1-TRAF2 Complex to Suppress Randall's
Liang Tang1,2,3, Zhangcheng Liao1,2,3,4, Meng Gao1,2,3
1Department of Urology, Xiangya Hospital, Central South University, Changsha, Hunan, China.
Abstract:
Calcium oxalate (CaOx) kidney stones are common and recur frequently, yet effective pharmacological prevention is limited. Randall's plaques (RPs), calcium deposits on renal papillae, act as anchoring sites for CaOx crystal growth, but the cellular origin and immunoregulatory mechanism underlying early calcium deposition remain unclear. Here, we found that early calcium deposition was partially localized to the renal interstitium surrounding aquaporin 2 (AQP2)-labeled collecting duct cells with apoptotic phenotype, and inhibiting high calcium-induced apoptosis of AQP2+ cells markedly reduced cell layer calcium deposition. Given the regulatory role of macrophages in renal stone formation, we revealed that M2 macrophages protected AQP2+ cells by delivering TRAF2 via exosomes. Mechanistically, exosomal TRAF2 interacted with intracellular TRAF1 to form a stable complex, which mutually inhibited their ubiquitin-mediated degradation by excluding the shared E3 ubiquitin ligase CBLC. This complex activated downstream nuclear factor κB1 (NF-κB1) and NF-κB2 signaling. NF-κB1 enhanced TRAF1 transcription, whereas NF-κB2 increased BCL2 expression while suppressing BAX and cleaved-PARP1, thereby limiting apoptosis and subsequent calcium deposition. Based on these findings, we developed M2 exosome-loaded, AQP2+ cell membrane-coated poly (lactic-co-glycolic acid) nanoparticles (Exo@A-P) for renal-targeted delivery. Exo@A-P treatment reduced collecting duct apoptosis and calcium deposition in hypercalciuria and renal calcified mice (Umod-/- ) without detectable toxicity, potentially supporting a targeted nanotherapeutic strategy to prevent early RP formation by utilizing TRAF2-rich exosome from M2 macrophages.
Insights
M2 macrophages protect kidney cells from calcium oxalate stone formation by delivering TRAF2 via exosomes. This mechanism, involving TRAF1 and NF-κB signaling, prevents apoptosis and calcium deposition, offering a potential nanotherapeutic strategy.
Area of Science:
- Nephrology
- Immunology
- Nanomedicine
Background:
- Calcium oxalate (CaOx) kidney stones are prevalent and recurrent, with limited pharmacological prevention options.
- Randall's plaques (RPs) are key sites for CaOx crystal growth, but their early cellular origins and immune regulation are poorly understood.
- Apoptosis of aquaporin 2 (AQP2)-positive collecting duct cells is implicated in early calcium deposition.
Purpose of the Study:
- To elucidate the cellular origin and immunoregulatory mechanisms of early calcium deposition in kidney stone formation.
- To investigate the role of M2 macrophages and their exosomal cargo in protecting renal cells from apoptosis and calcification.
- To develop and evaluate a targeted nanotherapeutic strategy for preventing RP formation.
Main Methods:
- Investigated calcium deposition in renal interstitium surrounding AQP2+ cells with apoptotic phenotypes.
- Examined the protective role of M2 macrophages and their exosome-mediated delivery of TRAF2.
- Analyzed the molecular mechanism involving TRAF2, TRAF1, CBLC, NF-κB1, NF-κB2, BCL2, BAX, and cleaved-PARP1.
- Developed and tested M2 exosome-loaded, AQP2+ cell membrane-coated nanoparticles (Exo@A-P) in mouse models.
Main Results:
- Inhibiting high calcium-induced apoptosis of AQP2+ cells reduced calcium deposition.
- M2 macrophages protected AQP2+ cells via exosomal TRAF2, which formed a complex with TRAF1, inhibiting degradation.
- This complex activated NF-κB signaling, promoting cell survival (BCL2) and reducing apoptosis (BAX, cleaved-PARP1).
- Exo@A-P treatment decreased apoptosis and calcium deposition in hypercalciuria and Umod-/- mice without toxicity.
Conclusions:
- M2 macrophage-derived exosomes carrying TRAF2 can prevent apoptosis of AQP2+ collecting duct cells, thereby reducing early calcium deposition and RP formation.
- The TRAF2-TRAF1-NF-κB pathway is crucial for regulating apoptosis and preventing renal calcification.
- Targeted delivery of M2 exosomes via engineered nanoparticles (Exo@A-P) shows promise for preventing kidney stone formation.
