Authors' Reply: Clarifying On-Target p38 Inhibition and Protein Restriction Effects in CKD-Associated Vascular Calcification

We thank Zhao et al.1 for their constructive comments on our recent JASN article, “High Phosphate and Low Protein Mediate Arterial and Cutaneous Vascular Calcification in CKD Mice.”2 We appreciate their thoughtful evaluation of our model and their suggestions to refine mechanistic interpretation and translational relevance. We agree that the pharmacologic specificity of SB203580 deserves consideration. SB203580 is known to selectively inhibit p38α/β while exerting limited effects on p38γ/δ and some off-target kinases at experimental concentrations.3 We chose this inhibitor on the basis of its established efficacy in vascular calcification models and well-characterized pharmacokinetic properties.4 Nonetheless, testing structurally distinct p38 inhibitors and using dominant-negative Mapk14 and smooth muscle–specific, tamoxifen-inducible p38α knockout mice (Myh11-CreERT2/Mapk14fl/fl) would provide important genetic validation. We also appreciate the suggestion to further dissect the synergistic effects of high phosphate and protein restriction. Our initial goal was to reproduce the clinical setting in which patients with CKD often exhibit both hyperphosphatemia and malnutrition. Although we measured aortic fetuin-A and matrix Gla protein, we agree that serial serum monitoring and pair-feeding approaches would clarify how systemic changes in calcification inhibitors and mineral balance parallel tissue mineralization. Moreover, fetuin-A supplementation studies would directly test the causality of the malnutrition–fetuin-A axis. Finally, we acknowledge that our study was limited to male C57BL/6J mice and a 4-week intervention, which may underestimate sex-specific and chronic effects. Future investigations will include both sexes and extended follow-up to capture the full spectrum of vascular and cutaneous pathology. We thank the correspondents again for their insightful feedback, which will help strengthen the mechanistic rigor and translational scope of this experimental platform.