pH-Dependent Expression, Stability, and Activity of Malassezia restricta MrLip5 Lipase

Epidermal barrier impairment predisposes for excessive growth of the allergy-associated yeast Malassezia on murine skin

BACKGROUND

The skin barrier is vital for protection against environmental threats including insults caused by skin-resident microbes. Dysregulation of this barrier is a hallmark of atopic dermatitis (AD) and ichthyosis, with variable consequences for host immune control of colonizing commensals and opportunistic pathogens. While Malassezia is the most abundant commensal fungus of the skin, little is known about the host control of this fungus in inflammatory skin diseases.

METHODS

In this experimental study, MC903-treated mice were colonized with Malassezia spp. to assess the host-fungal interactions in atopic dermatitis. Additional murine models of AD and ichthyosis, including tape stripping, K5-Nrf2 overexpression and flaky tail mice, were employed to confirm and expand the findings. Skin fungal counts were enumerated. High parameter flow cytometry was used to characterize the antifungal response in the AD-like skin. Structural and functional alterations in the skin barrier were determined by histology and transcriptomics of bulk skin. Finally, differential expression of metabolic genes in Malassezia in atopic and control skin was quantified.

RESULTS

Malassezia grows excessively in AD-like skin. Fungal overgrowth could, however, not be explained by the altered immune status of the atopic skin. Instead, we found that by upregulating key metabolic genes in the altered cutaneous niche, Malassezia acquired enhanced fitness to efficiently colonise the impaired skin barrier.

CONCLUSIONS

This study provides evidence that structural and metabolic changes in the dysfunctional epidermal barrier environment provide increased accessibility and an altered lipid profile, to which the lipid-dependent yeast adapts for enhanced nutrient assimilation. Our findings reveal fundamental insights into the implication of the mycobiota in the pathogenesis of common skin barrier disorders.

Heat-killed Lacticaseibacillus paracasei GMNL-653 ameliorates human scalp health by regulating scalp microbiome

BACKGROUND

The equilibrium of the scalp microbiome is important for maintaining healthy scalp conditions, including sebum secretion, dandruff, and hair growth. Many different strategies to improve scalp health have been reported; however, the effect of postbiotics, such as heat-killed probiotics, on scalp health remains unclear. We examined the beneficial effects of heat-killed probiotics consisting of Lacticaseibacillus paracasei, GMNL-653, on scalp health.

RESULTS

Heat-killed GMNL-653 could co-aggregate with scalp commensal fungi, Malassezia furfur, in vitro, and the GMNL-653-derived lipoteichoic acid inhibited the biofilm formation of M. furfur on Hs68 fibroblast cells. The mRNA of hair follicle growth factors, including insulin-like growth factor-1 receptor (IGF-1R), vascular endothelial growth factor, IGF-1, and keratinocyte growth factor was up-regulated in skin-related human cell lines Hs68 and HaCaT after treatment with heat-killed GMNL-653. For clinical observations, we recruited 22 volunteer participants to use the shampoo containing the heat-killed GMNL-653 for 5 months and subsequently measured their scalp conditions, including sebum secretion, dandruff formation, and hair growth. We applied polymerase chain reaction (PCR) to detect the scalp microbiota of M. restricta, M. globosa, Cutibacterium acnes, and Staphylococcus epidermidis. A decrease in dandruff and oil secretion and an increase in hair growth in the human scalp were observed after the use of heat-killed GMNL-653-containing shampoo. The increased abundance of M. globosa and the decreased abundance of M. restricta and C. acnes were also observed. We further found that accumulated L. paracasei abundance was positively correlated with M. globosa abundance and negatively correlated with C. acnes abundance. S. epidermidis and C. acnes abundance was negatively correlated with M. globosa abundance and positively correlated with M. restricta. Meanwhile, M. globosa and M. restricta abundances were negatively associated with each other. C. acnes and S. epidermidis abundances were statistically positively correlated with sebum secretion and dandruff, respectively, in our shampoo clinical trial.

CONCLUSION

Our study provides a new strategy for human scalp health care using the heat-killed probiotics GMNL-653-containing shampoo. The mechanism may be correlated with the microbiota shift.

Head and neck dermatitis is exacerbated by Malassezia furfur colonization, skin barrier disruption, and immune dysregulation

Introduction & objectives

Head and neck dermatitis (HND) is a refractory phenotype of atopic dermatitis (AD) and can be a therapeutic challenge due to lack of responsiveness to conventional treatments. Previous studies have suggested that the microbiome and fungiome may play a role in inducing HND, but the underlying pathogenic mechanisms remain unknown. This study aimed to determine the link between HND and fungiome and to examine the contribution of Malassezia furfur.

Materials and methods

To identify the effect of the sensitization status of M. furfur on HND, 312 patients diagnosed with AD were enrolled. To elucidate the mechanism underlying the effects of M. furfur, human keratinocytes and dermal endothelial cells were cultured with M. furfur and treated with Th2 cytokines. The downstream effects of various cytokines, including inflammation and angiogenesis, were investigated by real-time quantitative PCR. To identify the association between changes in lipid composition and M. furfur sensitization status, D-squame tape stripping was performed. Lipid composition was evaluated by focusing on ceramide species using liquid chromatography coupled with tandem mass spectrometry.

Results

Increased sensitization to M. furfur was observed in patients with HND. Additionally, sensitization to M. furfur was associated with increased disease severity in these patients. IL-4 treated human keratinocytes cultured with M. furfur produced significantly more VEGF, VEGFR, IL-31, and IL-33. IL-4/M. furfur co-cultured dermal endothelial cells exhibited significantly elevated VEGFR, TGF-β, TNF-α, and IL-1β levels. Stratum corneum lipid analysis revealed decreased levels of esterified omega-hydroxyacyl-sphingosine, indicating skin barrier dysfunction in HND. Finally, M. furfur growth was inhibited by the addition of these ceramides to culture media, while the growth of other microbiota, including Cutibacterium acnes, were not inhibited.

Conclusions

Under decreased levels of ceramide in AD patients with HND, M. furfur would proliferate, which may enhance pro-inflammatory cytokine levels, angiogenesis, and tissue remodeling. Thus, it plays a central role in the pathogenesis of HND in AD.

Skin Commensal Fungus Malassezia and Its Lipases

Malassezia is the most abundant genus in the fungal microflora found on human skin, and it is associated with various skin diseases. Among the 18 different species of Malassezia that have been identified to date, M. restricta and M. globosa are the most predominant fungal species found on human skin. Several studies have suggested a possible link between Malassezia and skin disorders. However, our knowledge on the physiology and pathogenesis of Malassezia in human body is still limited. Malassezia is unable to synthesize fatty acids; hence, it uptakes external fatty acids as a nutrient source for survival, a characteristic compensated by the secretion of lipases and degradation of sebum to produce and uptake external fatty acids. Although it has been reported that the activity of secreted lipases may contribute to pathogenesis of Malassezia, majority of the data were indirect evidences; therefore, enzymes' role in the pathogenesis of Malassezia infections is still largely unknown. This review focuses on the recent advances on Malassezia in the context of an emerging interest for lipases and summarizes the existing knowledge on Malassezia, diseases associated with the fungus, and the role of the reported lipases in its physiology and pathogenesis.