The Role of Cutaneous Microbiota Harmony in Maintaining a Functional Skin Barrier

Abstract

INTRODUCTION

Epithelial barrier dysfunctions in atopic dermatitis: a skin-gut-lung model linking microbiome alteration and immune dysregulation

“…Filaggrin ( FLG ) is a structural protein that is fundamental in forming the cornified cell envelope and maintaining intercellular cohesion . Breakdown of FLG generates alanine, pyrrolidone carboxylic acid and urocanic acid, natural moisturizing factors that preserve hydration, lower surface pH and contribute to skin antimicrobial defence . FLG deficiency leads to increased epidermal pH, which promotes serine protease activity to degrade SC desmosomes and inhibit CER production …”

“…Microflora composition is determined by one's sex, age, ethnicity, climate, UV exposure, and lifestyle (e.g. diet, hygiene habits and alcohol consumption) . A diverse skin microbiota has been shown to promote normal skin homeostasis through induction of Th17 cell immune response and secretion of antimicrobial peptides that nourish commensal flora and prevent growth of pathogenic species .…”

“…For example, Staphylococcus epidermidis is a commensal bacterium that suppresses inflammation after skin injury and enhances innate immunity . Staphylococcus epidermidis also restricts growth and reproduction of pathogenic gram‐positive species through competition for resources and secretion of antimicrobial peptides . Conversely, S. aureus colonization leads to skin breakdown and increased risk of AD development .…”

“…Periods of remission are associated with increased bacterial diversity, with more S. epidermidis and species of Streptococcus , Corynebacterium and Propionibacterium . This temporal shift in skin microflora may be related to skin structural barrier defects that permit penetration by pathogenic species and loss of protective species …”

“…The epidermal barrier is composed of the stratum corneum (SC) and tight junctions (TJs). 10 Epidermal barrier impairment in AD can result from altered lipid composition, dysfunctional and decreased structural proteins, increased skin pH and reduced skin microbiome diversity. Cutaneous permeability defects can be assessed by measuring transepidermal water loss (TEWL), which correlates with disease severity.…”