Innate immunology and microbial diversity in human skin diseases
Open Access
- Author:
- Schneider, Andrea
- Graduate Program:
- Biomedical Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 02, 2020
- Committee Members:
- Amanda Marie Nelson, Dissertation Advisor/Co-Advisor
Amanda Marie Nelson, Committee Chair/Co-Chair
Neil David Christensen, Committee Member
Lisa M Shantz, Committee Member
Todd Schell, Outside Member
Diane M Thiboutot, Committee Chair/Co-Chair
Ralph Lauren Keil, Program Head/Chair
Diane M Thiboutot, Dissertation Advisor/Co-Advisor - Keywords:
- Skin
Microbiome
Non-Melanoma Skin Cancer
Innate Immunity
Hidradenitis Suppurativa
Acne - Abstract:
- The work encompassed in this dissertation aims to elucidate interactions between our skin and the environment to understand their impact on health and disease. Ultraviolet (UV) radiation from the sun is an environmental exposure which leads to inflammation, genetic mutations, and non-melanoma skin cancer (NMSC). We observed that NMSCs expressed Toll-like-receptor 3 (TLR3) protein in both basal cell carcinomas (BCCs) and cutaneous squamous cell carcinomas (cSCCs). We hypothesized that UVB-induced keratinocyte damage leads to TLR3-dependent signaling which promotes an epithelial-to-mesenchymal transition (EMT) contributing to NMSC initiation. We observed TLR3 activation and a sustained EMT morphology in normal human epidermal keratinocytes (NHEKs) exposed to UVB or polyinosinic-polycytidylic acid (poly(I:C)), a synthetic TLR3 agonist. EMT-associated transcription factors (ZEB1, SNAI1, TWIST1), mesenchymal proteins (fibronectin, vimentin), and invasion capacity were all increased in NHEKs following TLR3 activation. In addition, this process was specific to TLR3 as activation of other TLRs did not induce this phenotypic change and both pharmacological and genetic inhibition of TLR3 attenuated EMT. Finally, TLR3 activation of EMT relied, in part, on NF-B signaling in keratinocytes. All together, these data suggest that TLR3 activation leads to EMT changes in keratinocytes which likely contribute to NMSC development. The skin is also home to a number of bacteria, viruses, and fungi, which can impact its overall health. Dysbiosis of the skin microbiome has been associated with a number of skin diseases including acne, where cutaneous bacteria contribute to increased inflammation, and atopic dermatitis, where bacteria enhance disruption of the skin barrier. We investigated the microbial environment in hidradenitis suppurativa (HS), an inflammatory skin disease characterized by painful nodules and abscesses in the axilla and groin regions where the role of cutaneous bacteria is not well understood. We sampled the follicular and skin surface microbiome of the axilla and groin of HS patients (non-lesion and lesion) and healthy individuals using 16S rRNA gene sequencing (V3-V4). Overall, we noted a global dysbiosis of the skin microbiome in HS patients that was characterized by a significant decrease in the skin commensal Cutibacterium and an increased abundance of opportunistic anaerobic pathogens. In addition, while healthy controls had distinct microbial signatures by body site and skin niche, HS patients lost this heterogeneity. Finally, using a computational approach, we identified significant alterations in the metabolic pathways of the HS microbiome compared to healthy controls and which microbes likely contributed to these metabolic pathways. Altogether, our data suggests that skin microbial dysbiosis in HS is influenced by the changing skin architecture and microenvironment and that the presence of these “abnormal” bacteria greatly influence the overall metabolic function of the skin community. How the skin microbial community and the skin interact with each other is important to restoring a healthy microbiome and skin microenvironment. Finally, we shifted our focus to understanding which features of the host can impact the microbial environment. To address this, we examined the effects of puberty and acne on the skin microbiome composition. In this study we sampled 48 individuals, ages 7-17, with and without acne. A significant shift in both -diversity and -diversity occurred between consecutive Tanner stages 2 and 3, highlighting a natural shift in the microbiome between early (T1-T2) and late (T3-T5) stages of puberty. The timing of this shift strongly coincided with the increase in sebum production in subjects. This shift was further characterized by a decrease in the numbers of distinct bacterial species and an increased abundance of Cutibacterium acnes, in both normal and acne patients. -diversity was very similar in children regardless of acne status, but an “acne microbiome signature” emerged for acne patients during late puberty. Strain level analysis of C. acnes demonstrated a significant shift in -diversity in normal subjects from early to late puberty, and in late puberty between normal and acne patients. This strain level diversity in C. acnes was primarily driven by changes in single locus sequencing type (SLST) clusters A and D. Finally, functional analysis by network mapping identified a significant shift in two metabolic pathways, Porphyrin and Chlorophyll Metabolism and Histidine Metabolism, which were most active in late (T3-T5) acne patients. Overall, we showed that puberty has the largest influence over changes in the skin microbiome, but as children mature, a distinct acne microbiome signature emerges in those patients with acne. In summary, our skin has the remarkable ability to withstand and respond to a variety of insults. The data presented in this dissertation illustrates the complexity of the interactions between the skin and its environment. In the long term, an understanding of these interactions may be key to optimizing or developing novel therapeutics for a variety of skin diseases.