Abstract
Staphylococci can sense Substance P (SP) in skin, but this molecule is generally released by nerve terminals along with another neuropeptide, Calcitonin Gene Related Peptide (CGRP). In this study, we investigated the effects of αCGRP on Staphylococci. CGRP induced a strong stimulation of Staphylococcus epidermidis virulence with a low threshold (<10−12 M) whereas Staphylococcus aureus was insensitive to CGRP. We observed that CGRP-treated S. epidermidis induced interleukin 8 release by keratinocytes. This effect was associated with an increase in cathelicidin LL37 secretion. S. epidermidis displayed no change in virulence factors secretion but showed marked differences in surface properties. After exposure to CGRP, the adherence of S. epidermidis to keratinocytes increased, whereas its internalization and biofilm formation activity were reduced. These effects were correlated with an increase in surface hydrophobicity. The DnaK chaperone was identified as the S. epidermidis CGRP-binding protein. We further showed that the effects of CGRP were blocked by gadolinium chloride (GdCl3), an inhibitor of MscL mechanosensitive channels. In addition, GdCl3 inhibited the membrane translocation of EfTu, the Substance P sensor. This work reveals that through interaction with specific sensors S. epidermidis integrates different skin signals and consequently adapts its virulence.
Highlights
Skin is the major neuroendocrine organ of the human body[1] and harbors a large and highly diverse microbiota[2]
The results are representative of three independent experiments
The effect of Calcitonin Gene Related Peptide (CGRP) on bacterial cytotoxicity was evaluated on HaCaT keratinocytes by measurement of lactate dehydrogenase (LDH), a stable cytosolic enzyme released during cell lysis[14]
Summary
Skin is the major neuroendocrine organ of the human body[1] and harbors a large and highly diverse microbiota[2]. We have previously shown that skin bacteria of different phyla, including gram-positive species such as Bacillus cereus[5], Staphylococcus aureus[5,6] and Staphylococcus epidermidis[5,6], and gram-negative bacteria such as Pseudomonas fluorescens[7] can detect Substance P (SP), the principle skin neuropeptide This molecule between nano- and micro-molar concentrations acts on bacteria and leads to a general increase in virulence. The effect of αCGRP on S. aureus and S. epidermidis virulence was investigated in cultured keratinocytes and reconstructed human epidermis to more closely simulate normal skin conditions. They are of the same genus, these bacteria had completely different sensitivities to CGRP. A schema was proposed to explain how S. epidermidis can sense and integrate different host signals and adapt its virulence in response to a cutaneous environment
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