Commensal microbiota regulates skin barrier function and repair via signaling through the aryl hydrocarbon receptor

The epidermis forms a barrier that defends the body from desiccation and entry of harmful substances, while also sensing and integrating environmental signals. The tightly orchestrated cellular changes needed for the formation and maintenance of this epidermal barrier occur in the context of the skin microbiome. Using germ-free mice, we demonstrate the microbiota is necessary for proper differentiation and repair of the epidermal barrier. These effects are mediated by microbiota signaling through the aryl hydrocarbon receptor (AHR) in keratinocytes, a xenobiotic receptor also implicated in epidermal differentiation. Mice lacking keratinocyte AHR are more susceptible to barrier damage and infection, during steady-state and epicutaneous sensitization. Colonization with a defined consortium of human skin isolates restored barrier competence in an AHR-dependent manner. We reveal a fundamental mechanism whereby the microbiota regulates skin barrier formation and repair, which has far-reaching implications for the numerous skin disorders characterized by epidermal barrier dysfunction.

Commensal microbiota modulate gene expression in the skin

BACKGROUND

The skin harbors complex communities of resident microorganisms, yet little is known of their physiological roles and the molecular mechanisms that mediate cutaneous host-microbe interactions. Here, we profiled skin transcriptomes of mice reared in the presence and absence of microbiota to elucidate the range of pathways and functions modulated in the skin by the microbiota.

RESULTS

A total of 2820 genes were differentially regulated in response to microbial colonization and were enriched in gene ontology (GO) terms related to the host-immune response and epidermal differentiation. Innate immune response genes and genes involved in cytokine activity were generally upregulated in response to microbiota and included genes encoding toll-like receptors, antimicrobial peptides, the complement cascade, and genes involved in IL-1 family cytokine signaling and homing of T cells. Our results also reveal a role for the microbiota in modulating epidermal differentiation and development, with differential expression of genes in the epidermal differentiation complex (EDC). Genes with correlated co-expression patterns were enriched in binding sites for the transcription factors Klf4, AP-1, and SP-1, all implicated as regulators of epidermal differentiation. Finally, we identified transcriptional signatures of microbial regulation common to both the skin and the gastrointestinal tract.

CONCLUSIONS

With this foundational approach, we establish a critical resource for understanding the genome-wide implications of microbially mediated gene expression in the skin and emphasize prospective ways in which the microbiome contributes to skin health and disease.

The preadolescent acne microbiome: A prospective, randomized, pilot study investigating characterization and effects of acne therapy

BACKGROUND/OBJECTIVES

Acne, a common pediatric disease, tends to be more comedonal in preadolescents, whereas older individuals are more likely to have inflammatory lesions in addition to comedones. Thus the microbiome of preadolescents may be different. In this pilot study we aimed to characterize the preadolescent acne microbiome, compare the microbiome in preadolescents with and without acne, and investigate changes in the microbiome after topical treatment with benzoyl peroxide or a retinoid in a small cohort of preadolescents.

METHODS

Participants were 7-10 years of age with (intervention group) or without (control group) acne and were recruited during routine outpatient dermatology visits. Baseline questionnaires, physical examination, and pore strip application were performed for all participants. Intervention group participants were randomized to receive topical therapy with benzoyl peroxide 5% gel or cream or tretinoin 0.025% cream. Participants with acne were followed up 8-10 weeks later and pore strip application was repeated.

RESULTS

Preadolescents with acne were colonized with a greater diversity of cutaneous bacteria than controls and the most commonly identified bacterium was Streptococcus. The number of bacterial species and phylogenetic diversity decreased after treatment with benzoyl peroxide and tretinoin.

CONCLUSION

The predominant bacteria in microbiome studies of adult acne is Propionibacterium, whereas in this pediatric population we saw a lot of Streptococcus bacteria. After treatment, the microbiomes of intervention group participants more closely resembled those of control group participants.

Analysis of the Stomal Microbiota of a Percutaneous Osseointegrated Prosthesis: A Longitudinal Prospective Cohort Study

Percutaneous osseointegrated (OI) prostheses (POPs) are used to skeletally attach artificial limbs in amputees. While any permanent percutaneous interface is at risk of becoming infected by the resident microbiota colonizing the stoma, most of these patients remain infection-free. Avoidance of infection likely depends upon a mechanically and/or biologically stable skin-to-implant interface. The ultimate question remains, "why do some stomata become infected while others do not?" The answer might be found in the dynamic bacterial communities of the patient and within the stomal site itself. This study is an appendix to the first Food and Drug Administration approved prospective early feasibility study of OI prosthetic docking, in which, 10 transfemoral amputees were implanted with a unique POP device. In this analytical, longitudinal cohort study, each patient's skin and stomal microbiota were analyzed from the initial surgery to 1 year following the second-stage surgery. During each follow-up visit, three swab samples-stomal, device thigh skin and contralateral thigh skin-were obtained. DNA was extracted, and bacterial 16S ribosomal RNA (rRNA) genes were amplified and sequenced to profile microbial communities. The stomal microbiota were distinct from the microbiota on the adjacent thigh skin and the skin of the contralateral thigh, with a significantly increased abundance of Staphylococcus aureus within the stoma. Early on stomal microbiota were characterized by high diversity and high relative abundance of obligate anaerobes. Over time, the stomal microbiota shifted and stabilized in communities of lower diversity dominated by Streptococcus, Corynebacterium, and/or Staphylococcus spp. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2645-2654, 2019.