TRAF3 Modulation: Novel Mechanism for the Anti-inflammatory Effects of the Vitamin D Receptor Agonist Paricalcitol in Renal Disease
Sandra Rayego‐Mateos, José Luis Morgado‐Pascual, José Manuel Valdivielso, Ana B. Sanz, Enrique Bosch‐Panadero, Raúl R. Rodrigues-Díez, Jesús Egido, Alberto Ortíz, Emilio González‐Parra, Marta Ruiz‐Ortega
Abstract
Significance Statement TNF receptor–associated factor 3 (TRAF3) downregulation is a key feature promoting inflammation in CKD, and noncanonical NF- κ B2 activation is a key driver of inflammation in this context. TRAF3 levels in PBMCs are decreased in patients on hemodialysis and could be a biomarker for the inflammatory state. Paricalcitol may reverse TRAF3 downregulation in a vitamin D receptor–independent manner, suggesting novel signaling pathways behind the anti-inflammatory effect of paricalcitol. Background CKD leads to vitamin D deficiency. Treatment with vitamin D receptor agonists (VDRAs) may have nephroprotective and anti-inflammatory actions, but their mechanisms of action are poorly understood. Methods Modulation of the noncanonical NF- κ B2 pathway and its component TNF receptor–associated factor 3 (TRAF3) by the VDRA paricalcitol was studied in PBMCs from patients with ESKD, cytokine-stimulated cells, and preclinical kidney injury models. Results In PBMCs isolated from patients with ESKD, TRAF3 protein levels were lower than in healthy controls. This finding was associated with evidence of noncanonical NF- κ B2 activation and a proinflammatory state. However, PBMCs from patients with ESKD treated with paricalcitol did not exhibit these features. Experiments in cultured cells confirmed the link between TRAF3 and NF- κ B2/inflammation. Decreased TRAF3 ubiquitination in K48-linked chains and cIAP1-TRAF3 interaction mediated the mechanisms of paricalcitol action.TRAF3 overexpression by CRISPR/Cas9 technology mimicked VDRA’s effects. In a preclinical model of kidney injury, paricalcitol inhibited renal NF- κ B2 activation and decreased renal inflammation. In VDR knockout mice with renal injury, paricalcitol prevented TRAF3 downregulation and NF- κ B2–dependent gene upregulation, suggesting a VDR-independent anti-inflammatory effect of paricalcitol. Conclusions These data suggest the anti-inflammatory actions of paricalcitol depend on TRAF3 modulation and subsequent inhibition of the noncanonical NF- κ B2 pathway, identifying a novel mechanism for VDRA’s effects. Circulating TRAF3 levels could be a biomarker of renal damage associated with the inflammatory state.