Absence of Cold-Inducible RNA-Binding Protein (CIRP) Promotes Angiogenesis and Regeneration of Ischemic Tissue by Inducing M2-Like Macrophage Polarization

Abstract

Cold-inducible RNA-binding protein (CIRP) is an intracellular RNA-chaperone and extracellular promoter of inflammation, which is increasingly expressed and released under conditions of hypoxia and cold stress. The functional relevance of CIRP for angiogenesis and regeneration of ischemic muscle tissue has never been investigated and is the topic of the present study. We investigated the role of CIRP employing CIRP deficient mice along with a hindlimb model of ischemia-induced angiogenesis. 1 and 7 days after femoral artery ligation or sham operation, gastrocnemius muscles of CIRP-deficient and wildtype mice were isolated and processed for (immuno-) histological analyses. CIRP deficient mice showed decreased ischemic tissue damage as evidenced by Hematoxylin and Eosin staining, whereas angiogenesis was enhanced as demonstrated by increased capillary/muscle fiber ratio and number of proliferating endothelial (CD31+/BrdU+) cells on day 7 after surgery. Moreover, CIRP deficiency resulted in a reduction of total leukocyte count (CD45+), neutrophils (myeloperoxidase, MPO+), neutrophil extracellular traps (NETs) (MPO+/CitH3+), and inflammatory M1-like polarized macrophages (CD68+/MRC1-), whereas the number of tissue regenerating M2-like polarized macrophages (CD68+/MRC1-) was increased in ischemic tissue samples. In summary, we show that the absence of CIRP ameliorates angiogenesis and regeneration of ischemic muscle tissue, most likely by influencing macrophage polarization in direction to regenerative M2-like macrophages.

The Absence of Extracellular Cold-Inducible RNA-Binding Protein (eCIRP) Promotes Pro-Angiogenic Microenvironmental Conditions and Angiogenesis in Muscle Tissue Ischemia

“…In anti-CIRP antibody-treated mice a predominance of the anti-inflammatory M2-like polarized macrophages at the ischemic muscle tissue site was observed, as compared to control mice (for an overview see Figure 6). Overall, the blockade of eCIRP enhanced angiogenesis in vivo, reminiscent of results obtained in CIRP-deficient mice [59], to indicate that eCIRP is mainly responsible for modulating angiogenesis. Figure 6.…”

“…Recently, we showed in a murine hindlimb model that the genetic ablation of CIRP (including eCIRP and iCIRP) improves angiogenesis and the regeneration of ischemic tissue damage, most likely through the predominance of regenerative anti-inflammatory M2like polarized macrophages and the reduced accumulation of neutrophils and NETs [59]. Whether these changes in leukocyte recruitment, macrophage polarization, and ameliorated angiogenesis are attributed to the lack of intra-or extracellular CIRP remains unclear so far.…”

C3 Deficiency Leads to Increased Angiogenesis and Elevated Pro-Angiogenic Leukocyte Recruitment in Ischemic Muscle Tissue

“…Interestingly, this group already hypothesized that their findings might not be only restricted to the retinal. In our study on ischemic muscle tissue, we found in C3-deficient mice a reduced number of M1-like polarized macrophages but an increased number of M2-like polarized macrophages, which are well described for their pro-angiogenic function [ 67 , 68 ].…”

Cold-Induced RNA-Binding Protein Promotes Glucose Metabolism and Reduces Apoptosis by Increasing AKT Phosphorylation in Mouse Skeletal Muscle Under Acute Cold Exposure

“…CIRP mainly regulates the transcription and processing of RNA in the nucleus, and the translation and transformation of mRNA in the cytoplasm ( Zhu et al, 2016 ; Zhong and Huang, 2017 ). CIRP participates in multiple cell physiological activities through its regulation of targets ( Xia et al, 2012 ), for example, cell survival, proliferation, circadian rhythm regulation, telomere maintenance, tumor formation and development ( Zhong and Huang, 2017 ; Indacochea et al, 2021 ; Kübler et al, 2021 ). CIRP expression has been detected in various tissues and cells, especially in mild hypothermia ( Liu et al, 2019 ), hypoxia ( Wellmann et al, 2004 ), UV radiation ( Sun et al, 2018 ), heat stress ( Nishiyama et al, 1998 ), endoplasmic reticulum stress ( Khan et al, 2017 ), and oxidative stress ( De Leeuw et al, 2007 ), where its expression is up-regulated and respond to a variety of stress conditions by changing its expression and regulating mRNA stability through its binding site on the 3′-UTR of its targeted mRNAs ( Zhong and Huang, 2017 ; Zhong et al, 2021 ).…”