Activation and targetability of TYMP–IL-6–TF signaling in the skin microenvironment in uremic calciphylaxis

Calciphylaxis is an orphan disease characterized by dermal microvessel thrombosis, inflicting painful cutaneous necrosis. It occurs predominantly in patients with end-stage kidney disease and has high mortality, elusive pathogenesis, and no approved therapies. We demonstrate that sera from patients with calciphylaxis induced de novo synthesis of interleukin-6 (IL-6) and soluble IL-6 receptor (IL-6R) and stimulated Janus kinase-2 (JAK) and signal transducer and activator of transcription (STAT)-3 phosphorylation in primary human dermal microvascular endothelial cells (ECs). Calciphylaxis skin demonstrated an altered microenvironment characterized by a gain of proximal and distal IL-6 ligand-receptor interactions. Microvessels are the predominant senders and recipients of IL-6 signaling, which, along with up-regulated A disintegrin and metalloproteinase 17 in dermal vasculature and interstitial IL-6R, supported trans-IL-6 signaling in calciphylaxis lesions. Calciphylaxis serum up-regulated thymidine phosphorylase (TYMP) in ECs. TYMP up-regulated IL-6, which activated tissue factor (TF), a primary trigger of the extrinsic coagulation cascade. IL-6-TF signaling in ECs was partially triggered by elevated IL-6 and kynurenine amounts in calciphylaxis serum and was inhibited by anti-IL-6 treatment. The TF-inducing ability of calciphylaxis serum is correlated with disease activity and response to IL-6 inhibitors in ECs. Calciphylaxis is therefore a combination of serum-inducing TYMP-IL-6-TF signaling in ECs and a heterogeneous permissive local dermal microenvironment. The latter is characterized by microvessels initiating IL-6 signaling and multiway cross-talk with adipocytes and eccrine glands, perpetuating the sinister thrombotic milieu. Our results support exploring the IL-6-TF-inducing ability of calciphylaxis serum as an activity marker and IL-6 as a therapeutic target for uremic calciphylaxis.