P2Y6 promoted pruning of FSTL1 nerves by cutaneous macrophages to reset pain threshold and cardiac function

Hyperactivation of cutaneous macrophages promotes the development of chronic pain. Stimulation of nociceptive regions promotes neuroplasticity, which affects pain perception and related physiological responses. However, the specific mechanisms by which cutaneous macrophages sense and elicit nociceptive responses are unknown. Here, we exacerbated the reduction of systemic pain threshold after chronic heart failure (CHF) by silencing follistatin-like 1 (FSTL1), especially the abnormal cutaneous nociceptive sensation at PC6 acupoint, the site associated with cardiac involvement pain. The upregulation of P2Y6 and interleukin-27 expression is intimately linked to the activation of skin macrophages. Hyperactivation of P2Y6 receptor (P2Y6R) may be associated with MHC II M1⁺ macrophage polarization in PC6. Thus, P2Y6 is one of the key factors that modulate the functional polarization of skin macrophages, which may subsequently influence the expansion of the pain field. The supportive effect of CD206 M2⁺ macrophages on the cutaneous FSTL1⁺ nerves was significantly reduced. Meanwhile, FSTL1⁺ nerves in PC6 functionally interacted with calcitonin gene-related peptide (CGRP)⁺ nerves, and the overactivation of nerve growth factor (NGF) secreted by cutaneous macrophages induced CGRP⁺ neuropathological remodeling, which supported the enlargement of the pain sensory area. The activation of CGRP and P2X3 receptor (P2X3R), Na⁺/K⁺ ATPase (NKA), and P2X3R in the C8 DRG may be one of the molecular bases mediating cutaneous nociceptive transmission and affecting the function of the heart. Hyperactivation of NKA was consistent with decreased pain threshold and changes in cardiac dysfunction, and PC6 injection of an NKA inhibitor (digilanid C) was effective in ameliorating nociception and cardiac impairment. The beneficial effects of digilanid C were counteracted by FSTL1 silencing. These results indicated that P2Y6 mediates the remodeling of pain perception by skin macrophages via the action of FSTL1, while NKA inhibitors synergistically exert their therapeutic effects.