Staphylococcus aureus Triggers Induction of miR-15B-5P to Diminish DNA Repair and Deregulate Inflammatory Response in Diabetic Foot Ulcers

Abstract

Diabetic foot ulcers (DFUs) are a debilitating complication of diabetes in which bacterial presence, including the frequent colonizer Staphylococcus aureus, contributes to inhibition of healing. MicroRNAs (miRs) play a role in healing and host response to bacterial pathogens. However, the mechanisms by which miR response to cutaneous S. aureus contributes to DFU pathophysiology are unknown. Here, we show that S. aureus inhibits wound closure and induces miR-15b-5p in acute human and porcine wound models and in chronic DFUs. Transcriptome analyses of DFU tissue showed induction of miR-15b-5p to be critical, regulating many cellular processes, including DNA repair and inflammatory response, by suppressing downstream targets IKBKB, WEE1, FGF2, RAD50, MSH2, and KIT. Using a human wound model, we confirmed that S. aureus-triggered miR-15b-5p induction results in suppression of the inflammatory- and DNA repair-related genes IKBKB and WEE1. Inhibition of DNA repair and accumulation of DNA breaks was functionally confirmed by the presence of the pH2AX within colonized DFUs. We conclude that S. aureus induces miR-15b-5p, subsequently repressing DNA repair and inflammatory response, showing a mechanism of inhibition of healing in DFUs previously unreported, to our knowledge. This underscores a previously unknown role of DNA damage repair in the pathophysiology of DFUs colonized with S. aureus.

A tractable, simplified ex vivo human skin model of wound infection

“…Of interest is the noted separation at the dermal‐epidermal junction in the infected wounds (Figure ). This was previously noted in ex vivo human skin wounds infected with S. aureus and may be due to the release of Staphopain A, virulence factors and/or other extracellular proteases with collagenolytic activity during the invasion of the wound bed . This provides yet another interesting prospect for future investigation.…”

Descriptive vs mechanistic scientific approach to study wound healing and its inhibition: Is there a value of translational research involving human subjects?

“…Although the etiology of VLU, DFU and PU is multifactorial, these wounds share some common recognizable defects . These common features of non‐healing wound pathophysiology include hyperproliferative non‐migratory epidermis, unresolved inflammation, impaired fibroblasts function, extracellular matrix deposition, increased levels of proteases, decreased angiogenesis and complex microbial communities associated with biofilms …”

“…Here, we outline studies that have successfully utilized a combined approach of using “omics” and patient samples to pinpoint specific processes and molecules associated with healing impairment. Gene expression profiling has been employed to identify specific sets of genes and corresponding microRNAs (miRs) that are deregulated in VLU and DFU tissue samples . Furthermore, comparative genomic analyses were employed to elucidate transcriptional features that distinguish chronic VLU from acute healing wounds (AW) .…”

“…The most recent study focused on identifying genes, associated pathways and miRs in DFU as a result of Staphylococcus aureus colonization. S. aureus induced miR‐15b‐5p, subsequently repressing DNA repair and diminishing inflammatory response, revealing a novel mechanism of healing inhibition in chronic DFU colonized with this pathogen . DFU are also characterized by a significant reduction of miR‐132, which contributes to the deregulation of inflammation‐related pathways such as NF‐κB, NOD‐like receptor, Toll‐like receptor and TNF‐α signalling .…”

“…The resulting specimens collected from debridement can be classified accordingly into three groups: callus only, partial specimens (containing callus with some epidermis) and complete specimens (containing callus, the full thickness epidermis and a portion of the dermis) . The presence of a full thickness epidermis and dermis proved to be an essential determinant of a high‐quality tissue sample, as only complete specimens were viable for further biomarker assessment, RNA isolation and gene expression analysis . However, up to one‐third of the total collected biopsies were callus only or partial specimens, and as such did not yield quality biomaterial useful for further analyses.…”