At an injury site, efficient clearance of apoptotic cells by wound macrophages or efferocytosis is a prerequisite for the timely resolution of inflammation. Emerging evidence indicates that microRNA-21 (miR-21) may regulate the inflammatory response. In this work, we sought to elucidate the significance of miR-21 in the regulation of efferocytosis-mediated suppression of innate immune response, a key process implicated in resolving inflammation following injury. An increased expression of inducible miR-21 was noted in postefferocytotic peripheral blood monocyte-derived macrophages. Such induction of miR-21 was associated with silencing of its target genes PTEN and PDCD4. Successful efferocytosis of apoptotic cells by monocyte-derived macrophages resulted in the suppression of LPS-induced NF-κB activation and TNF-α expression. Interestingly, bolstering of miR-21 levels alone, using miR mimic, resulted in significant suppression of LPS-induced TNF-α expression and NF-κB activation. We report that efferocytosis-induced miR-21, by silencing PTEN and GSK3β, tempers the LPS-induced inflammatory response. Macrophage efferocytosis is known to trigger the release of anti-inflammatory cytokine IL-10. This study demonstrates that following successful efferocytosis, miR-21 induction in macrophages silences PDCD4, favoring c-Jun–AP-1 activity, which in turn results in elevated production of anti-inflammatory IL-10. In summary, this work provides direct evidence implicating miRNA in the process of turning on an anti-inflammatory phenotype in the postefferocytotic macrophage. Elevated macrophage miR-21 promotes efferocytosis and silences target genes PTEN and PDCD4, which in turn accounts for a net anti-inflammatory phenotype. Findings of this study highlight the significance of miRs in the resolution of wound inflammation.

In chronic wounds, biofilm infects host tissue for extended periods of time. This work establishes the first chronic pre-clinical model of wound biofilm infection aimed at addressing long-term host response. Although biofilm infected wounds did not show marked differences in wound closure, the repaired skin demonstrated compromised barrier function. This observation is clinically significant because it leads to the notion that even if a biofilm infected wound is closed as observed visually, it may be complicated by the presence of failed skin which is likely to be infected and or further complicated post-closure. Study of underlying mechanisms recognized for the first time biofilm-inducible miR-146a and miR-106b in the host skin wound-edge tissue. These miRs silenced ZO-1 and ZO-2 to compromise tight junction function resulting in leaky skin as measured by transepidermal water loss. Intervention strategies aimed at inhibiting biofilm-inducible miRNAs may be productive in restoring barrier function of host skin.

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SUMMARY Monocytes and macrophages (mϕ) are plastic cells whose functions are governed by microenvironmental cues. Wound fluid bathing the wound tissue reflects the wound microenvironment. Current literature on wound inflammation is primarily based on the study of blood monocyte-derived mϕ (MDM), cells that have never been exposed to the wound microenvironment. We sought to pair-match compare MDMs with mϕ isolated from chronic wound of patients. Oncostatin M (OSM) was differentially overexpressed in pair-matched wound mϕ. Both PGE2 and its metabolite 13,14-dihydro-15-keto-PGE2 (PGE-M) were abundant in wound fluid and induced OSM in wound-site mϕ. Consistently, induction of OSM mRNA was observed in mϕ isolated from PGE2–enriched PVA sponges implanted in murine wounds. Treatment of human THP-1 cell-derived mϕ with PGE2 or PGE-M caused dose-dependent induction of OSM. Characterization of the signal transduction pathways demonstrated the involvement of EP4 receptor and cAMP signaling. In human mϕ, PGE2 phosphorylated Axl, a receptor tyrosine kinase (RTK). Axl phosphorylation was also induced by a cAMP analog demonstrating interplay between the cAMP and RTK pathways. PGE2–dependent Axl phosphorylation led to AP-1 transactivation which is directly implicated in inducible expression of OSM. Treatment of human mϕ or mice excisional wounds with recombinant OSM resulted in an anti-inflammatory response as manifested by attenuated expression of endotoxin-induced TNFα and IL-1β. OSM treatment also improved wound closure during the early inflammatory phase of healing. In summary this work recognizes PGE2 in the wound-fluid as a potent inducer of mϕ OSM, a cytokine with anti-inflammatory role in cutaneous wound healing.