Differences in Wound Healing in Mice with Deficiency of IL-6 versus IL-6 Receptor

Abstract

IL-6 modulates immune responses and is essential for timely wound healing. As the functions mediated by IL-6 require binding to its specific receptor, IL-6Rα, it was expected that mice lacking IL-6Rα would have the same phenotype as IL-6–deficient mice. However, although IL-6Rα–deficient mice share many of the inflammatory deficits seen in IL-6–deficient mice, they do not display the delay in wound healing. Surprisingly, mice with a combined deficit of IL-6 and IL-6Rα, or IL-6–deficient mice treated with an IL-6Rα–blocking Ab, showed improved wound healing relative to mice with IL-6 deficiency, indicating that the absence of the receptor contributed to the restoration of timely wound healing, rather than promiscuity of IL-6 with an alternate receptor. Wounds in mice lacking IL-6 showed delays in macrophage infiltration, fibrin clearance, and wound contraction that were not seen in mice lacking IL-6Rα alone and were greatly reduced in mice with a combined deficit of IL-6 and IL-6Rα. MAPK activation-loop phosphorylation was elevated in wounds of IL-6Rα–deficient mice, and treatment of wounds in these mice with the MEK inhibitor U0126 resulted in a delay in wound healing suggesting that aberrant ERK activation may contribute to improved healing. These findings underscore a deeper complexity for IL-6Rα function in inflammation than has been recognized previously.

Shedding of Endogenous Interleukin-6 Receptor (IL-6R) Is Governed by A Disintegrin and Metalloproteinase (ADAM) Proteases while a Full-length IL-6R Isoform Localizes to Circulating Microvesicles

“…ADAM10, or even an entirely different mechanism is responsible for serum sIL-6R generation. Here, we show that conditional ablation of ADAM10 in myeloid cells, which have been reported to generate the bulk (63%) of blood-borne sIL-6R (18), also resulted in unaltered sIL-6R serum levels. We further excluded neutrophil elastase, cathepsin G, and proteinase 3, which are highly abundant in myeloid cells, from contributing to sIL-6R generation in mouse as well as human blood.…”

“…cDNA was synthesized from 1 g of RNA with RevertAid TM Moloney MuLV reverse transcriptase (Fermentas, Thermo Scientific) using oligo(dT) 18 primer. Murine IL-6R mRNA transcripts were amplified via PCR using the following primers: mu IL-6R forward 1, 5Ј-AAG GAG GAG CTT GAC CTT GG-3Ј (Exon 6); mu IL-6R reverse 1, 5Ј-GTG GAG GAG AGG TCG TCT TG-3Ј (Exon 10); mu IL-6R forward 5UTR, 5Ј-GTG CGA GCT GAG TGT GGA G-3Ј; mu IL-6R forward Exon1, 5Ј-GGC TGC ACG CTG TTG GTC-3Ј; and mu IL-6R forward Exon4, 5Ј-ACA GTG TGG GAA GCA AGT CC-3Ј.…”

“…This indicates that either a different protease or an entirely different mode of generation contributes to circulating sIL-6R. Over 60% of serum sIL-6R in the mouse stem from myeloid cells, whereas the remainder can be attributed to hepatocytes and T cells (18). Given the role of ADAM10 as constitutive sheddase of endogenous IL-6R in monocytes and macrophages we reasoned that ADAM10 might be a good candidate for the protease generating circulating sIL-6R.…”

“…5A). RNA used for cDNA synthesis was isolated from organs or cells, which exhibit high IL-6R expression and have been shown to contribute to circulating sIL-6R levels (18). However, in contrast to human sIL-6R (Refs.…”

17β-estradiol ameliorates age-associated loss of fibroblast function by attenuating IFN-γ/STAT1-dependent miR-7 upregulation

“…IL6 can display pro‐ and anti‐inflammatory actions: IL6‐KO mice exhibit impaired granulation tissue formation and delayed cutaneous wound healing; IL6‐KO dermal fibroblasts had decreased production of matrix enzymes, suggesting an IL6 role in modulating fibroblast function (Luckett & Gallucci, 2007). One later study demonstrated that IL6Rα‐ERK signaling improved wound healing (McFarland‐Mancini et al ., 2010). In contrast to IL6, IFN‐γ decreased formation of new granulation tissue in rats and dysregulated collagen production and in vitro experiments demonstrated that IFN‐γ decreased collagen synthesis in rat fibroblasts (Laato et al ., 2001).…”