IFN-γ blockade after genetic inhibition of PD-1 aggravates skeletal muscle damage and impairs skeletal muscle regeneration

Abstract

Background Innate immune responses play essential roles in skeletal muscle recovery after injury. Programmed cell death protein 1 (PD-1) contributes to skeletal muscle regeneration by promoting macrophage proinflammatory to anti-inflammatory phenotype transition. Interferon (IFN)-γ induces proinflammatory macrophages that appear to hinder myogenesis in vitro. Therefore, we tested the hypothesis that blocking IFN-γ in PD-1 knockout mice may dampen inflammation and promote skeletal muscle regeneration via regulating the macrophage phenotype and neutrophils. Methods Anti-IFN-γ antibody was administered in PD-1 knockout mice, and cardiotoxin (CTX) injection was performed to induce acute skeletal muscle injury. Hematoxylin and eosin (HE) staining was used to view morphological changes of injured and regenerated skeletal muscle. Masson’s trichrome staining was used to assess the degree of fibrosis. Gene expressions of proinflammatory and anti-inflammatory factors, fibrosis-related factors, and myogenic regulator factors were determined by real-time polymerase chain reaction (PCR). Changes in macrophage phenotype were examined by western blot and real-time PCR. Immunofluorescence was used to detect the accumulation of proinflammatory macrophages, anti-inflammatory macrophages, and neutrophils. Results IFN-γ blockade in PD-1 knockout mice did not alleviate skeletal muscle damage or improve regeneration following acute cardiotoxin-induced injury. Instead, it exacerbated skeletal muscle inflammation and fibrosis, and impaired regeneration via inhibiting macrophage accumulation, blocking macrophage proinflammatory to anti-inflammatory transition, and enhancing infiltration of neutrophils. Conclusion IFN-γ is crucial for efficient skeletal muscle regeneration in the absence of PD-1.

Effects of immune exhaustion and senescence of innate immunity in autoimmune disorders

“…PD-1 contributes to skeletal muscle regeneration by facilitating the transition of macrophages from a proinflammatory to an anti-inflammatory phenotype ( 57 ). IFN-γ, on the other hand, stimulates the formation of proinflammatory macrophages, which seem to impede myogenesis in vitro ( 57 ).…”

“…PD-1 contributes to skeletal muscle regeneration by facilitating the transition of macrophages from a proinflammatory to an anti-inflammatory phenotype ( 57 ). IFN-γ, on the other hand, stimulates the formation of proinflammatory macrophages, which seem to impede myogenesis in vitro ( 57 ). However, Zhuang et al ( 57 ) surprisingly revealed that blocking IFN-γ signaling of PD-1 knockout models actually exacerbated inflammation in the injured muscle, impeded muscle regeneration, and intensified muscle fibrosis.…”

“…IFN-γ, on the other hand, stimulates the formation of proinflammatory macrophages, which seem to impede myogenesis in vitro ( 57 ). However, Zhuang et al ( 57 ) surprisingly revealed that blocking IFN-γ signaling of PD-1 knockout models actually exacerbated inflammation in the injured muscle, impeded muscle regeneration, and intensified muscle fibrosis. This detrimental effect was attributed to the inhibition of macrophage infiltration and transition from a proinflammatory to an anti-inflammatory state, associated with an increased influx of neutrophils into the muscle tissue.…”