The antimicrobial activity of chemerin-derived peptide p4 requires oxidative conditions

Systematic alanine and stapling mutational analysis of antimicrobial peptide Chem-KVL

Chem-KVL is a tandem repeating peptide, with 14 amino acids that was modified based on a short peptide from a fragment of the human host defense protein chemerin. Chem-KVL increases cationicity and hydrophobicity and shows broad-spectrum antibacterial activity. To determine the molecular determinants of Chem-KVL and whether staple-modified Chem-KVL would improve antibacterial activity and protease stability or decrease cytotoxicity, we combined alanine and stapling scanning, and designed a series of alanine and staple-derived Chem-KVL peptides, termed Chem-A1 to Chem-A14 and SCL-1 to SCL-7. We next examined their antibacterial activity against several gram-positive and gram-negative bacteria, their proteolytic stability, and their cytotoxicity. Ala scanning of Chem-KVL suggested that both the positively charged residues (Lys and Arg) and the hydrophobic residues (Lue and Val) were critical for the antibacterial activities of Chem-KVL peptide. Of note, Chem-A4 was able to remarkably inhibit the growth of gram-positive and gram-negative bacteria when compared to the original peptide. And the antibacterial activities of stapled SCL-4 and SCL-7 were several times higher than those of the linear peptide against gram-positive and gram-negative bacteria. Stapling modification of peptides resulted in increased helicity and protein stability when compared with the linear peptide. These stapled peptides, especially SCL-4 and SCL-7, may serve as the leading compounds for further optimization and antimicrobial therapy.

The chemerin-CMKLR1 axis in keratinocytes impairs innate host defense against cutaneous Staphylococcus aureus infection

The skin is the most common site of Staphylococcus aureus infection, which can lead to various diseases, including invasive and life-threatening infections, through evasion of host defense. However, little is known about the host factors that facilitate the innate immune evasion of S. aureus in the skin. Chemerin, which is abundantly expressed in the skin and can be activated by proteases derived from S. aureus, has both direct bacteria-killing activity and immunomodulatory effects via interactions with its receptor CMKLR1. Here, we demonstrate that a lack of the chemerin/CMKLR1 axis increases the neutrophil-mediated host defense against S. aureus in a mouse model of cutaneous infection, whereas chemerin overexpression, which mimics high levels of chemerin in obese individuals, exacerbates S. aureus cutaneous infection. Mechanistically, we identified keratinocytes that express CMKLR1 as the main target of chemerin to suppress S. aureus-induced IL-33 expression, leading to impaired skin neutrophilia and bacterial clearance. CMKLR1 signaling specifically inhibits IL-33 expression induced by cell wall components but not secreted proteins of S. aureus by inhibiting Akt activation in mouse keratinocytes. Thus, our study revealed that the immunomodulatory effect of the chemerin/CMKLR1 axis mediates innate immune evasion of S. aureus in vivo and likely increases susceptibility to S. aureus infection in obese individuals.

Plasma Chemerin Is Induced in Critically Ill Patients with Gram-Positive Infections

Chemerin is a chemoattractant protein abundantly expressed in hepatocytes. Chemerin exerts pro- and anti-inflammatory effects and acts as a pro-resolving protein. Chemerin levels are low in patients with liver cirrhosis and are increased in sepsis. The aim of this study was to identify associations between plasma chemerin levels and underlying diseases as well as causes of severe illness. The cohort included 32 patients with liver cirrhosis who had low systemic chemerin, and who were not considered for further evaluation. Plasma chemerin levels were similar between the 27 patients with systemic inflammatory response syndrome (SIRS), the 34 patients with sepsis and the 63 patients with septic shock. Chemerin in plasma correlated with C-reactive protein and leukocyte count but not with procalcitonin, a clinical marker of bacterial infection. Plasma chemerin did not differ among patients with and without ventilation and patients with and without dialysis. Vasopressor therapy was not associated with altered plasma chemerin levels. Infection with severe acute respiratory syndrome coronavirus 2 had no effect on plasma chemerin levels. Baseline levels of plasma chemerin could not discriminate between survivors and non-survivors. Notably, Gram-positive infection was associated with higher chemerin levels. In summary, the current study suggests that plasma chemerin might serve as an early biomarker for the diagnosis of Gram-positive infections in patients with sepsis.

Urinary chemerin as a potential biomarker for inflammatory bowel disease

Purpose

Systemic levels of the adipokine chemerin are elevated in different inflammatory conditions such as inflammatory bowel disease (IBD). In IBD, chemerin protein expression in colon mucosa is induced and serum chemerin levels are increased. Aim of this study was to identify chemerin protein in human feces and/or urine and to evaluate a possible association with IBD activity.

Materials and methods

Feces and urine of 40 patients with IBD and the respective sera of 34 patients were collected. Chemerin levels were analyzed by immunoblot in feces and urine samples. In addition, enzyme-linked immunosorbent assay (ELISA) was used to measure chemerin in all urine, feces and serum samples of the patients and in urine of 17 healthy controls.

Results

Chemerin was not detectable in 80% of the human feces samples by ELISA. Chemerin in human urine was detected by immunoblot and ELISA. Compared to serum levels, urinary concentration was about 6,000-fold lower. Urinary chemerin did not differ between patients with ulcerative colitis (n = 15) and Crohn's disease (n = 25). Urinary chemerin was not related to its serum levels, did not correlate with serum C-reactive protein level and negatively correlated with serum creatinine. Of note, urinary chemerin of patients with a fecal calprotectin > 500 μg/g was significantly higher compared to patients with lower calprotectin levels and compared to healthy controls. Serum creatinine did not differ between the patient groups.

Conclusion

Urinary chemerin might present a novel non-invasive biomarker for monitoring IBD severity and clinical course.

Antimicrobial Properties of a Peptide Derived from the Male Fertility Factor kl2 Protein of Drosophila melanogaster

Antimicrobial peptides (AMPs) are important components of innate immunity. Here, we report the antimicrobial properties of a peptide derived from the Male fertility factor kl2 (MFF-kl2) protein of Drosophila melanogaster, which was identified as a functional analog of the mammalian antibacterial chemerin-p4 peptide. The antimicrobial activity of multifunctional chemerin is mainly associated with a domain localized in the middle of the chemerin sequence, Val66-Pro85 peptide (chemerin-p4). Using bioinformatic tools, we found homologs of the chemerin-p4 peptide in the proteome of D. melanogaster. One of them is MFF-p1, which is a part of the MFF kl2 protein, encoded by the gene male fertility factor kl2 (kl-2) located on the long arm of the Y chromosome. The second detected peptide (Z-p1) is a part of the Zizimin protein belonging to DOCK family, which is involved in cellular signaling processes. After testing the antimicrobial properties of both peptides, we found that only MFF-p1 possesses these properties. Here, we demonstrate its antimicrobial potential both in vitro and in vivo after infecting D. melanogaster with bacteria. MFF-p1 strongly inhibits the viable counts of E. coli and B. subtilis after 2 h of treatment and disrupts bacterial cells. The expression of kl-2 is regulated by exposure to bacteria and by the circadian clock.

Circulating Chemerin and Its Kinetics May Be a Useful Diagnostic and Prognostic Biomarker in Critically Ill Patients with Sepsis: A Prospective Study

Chemerin, a novel adipokine, is a potent chemoattractant molecule with antimicrobial properties, implicated in immune responses. Our aim was to investigate circulating chemerin and its kinetics, early in sepsis in critically ill patients and its association with severity and prognosis. Serum chemerin was determined in a cohort of 102 critically ill patients with sepsis during the first 48 h from sepsis onset and one week later, and in 102 age- and gender-matched healthy controls. Patients were followed for 28 days and their outcomes were recorded. Circulating chemerin was significantly higher in septic patients at onset compared to controls (342.3 ± 108.1 vs. 200.8 ± 40.1 μg/L, p < 0.001). Chemerin decreased significantly from sepsis onset to one week later (342.3 ± 108.1 vs. 308.2 ± 108.5 μg/L, p < 0.001), but remained higher than in controls. Chemerin was higher in patients presenting with septic shock than those with sepsis (sepsis onset: 403.2 ± 89.9 vs. 299.7 ± 99.5 μg/L, p < 0.001; one week after: 374.9 ± 95.3 vs. 261.6 ± 91.9 μg/L, p < 0.001), and in nonsurvivors than survivors (sepsis onset: 427.2 ± 96.7 vs. 306.9 ± 92.1 μg/L, p < 0.001; one week after: 414.1 ± 94.5 vs. 264.2 ± 79.9 μg/L, p < 0.001). Moreover, patients with septic shock and nonsurvivors, presented a significantly lower absolute and relative decrease in chemerin one week after sepsis onset compared to baseline (p < 0.001). Based on ROC curve analyses, the diagnostic performance of chemerin (AUC 0.78, 95% CI 0.69–0.87) was similar to C-reactive protein (CRP) (AUC 0.78, 95% CI 0.68–0.87) in discriminating sepsis severity. However, increased chemerin at sepsis onset and one week later was an independent predictor of 28-day mortality (sepsis onset: HR 3.58, 95% CI 1.48–8.65, p = 0.005; one week after: HR 10.01, 95% CI 4.32–23.20, p < 0.001). Finally, serum chemerin exhibited significant correlations with the severity scores, white blood cells, lactate, CRP and procalcitonin, as well as with biomarkers of glucose homeostasis, but not with cytokines and soluble urokinase-type plasminogen activator receptor (suPAR). Circulating chemerin is increased early in sepsis and its kinetics may have diagnostic and prognostic value in critically ill patients. Further studies are needed to shed light on the role of chemerin in sepsis.

Chemerin-Derived Peptide Val66-Pro85 Is Effective in Limiting Methicillin-Resistant S. aureus Skin Infection

Chemerin-derived peptide Val⁶⁶-Pro⁸⁵ (p4) restricts the growth of a variety of skin-associated bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). To better understand the antimicrobial potential of chemerin peptide, we compared p4 activity against MRSA in vitro to cathelicidin LL-37, one of the key endogenous peptides implicated in controlling the growth of S. aureus. The efficacy of p4 was also validated in relevant experimental models of skin pathology, such as topical skin infection with community-acquired MRSA, and in the context of skin inflammatory diseases commonly associated with colonization with S. aureus, such as atopic dermatitis (AD). We showed that p4 collaborates additively with LL-37 in inhibiting the growth of S. aureus, including MRSA, and that p4 was effective in vivo in reducing MRSA burden. p4 was also effective in reducing levels of skin-infiltrating leukocytes in S. aureus-infected AD-like skin. Taken together, our data suggest that p4 is effective in limiting S. aureus and, in particular, MRSA skin infection.

Tandem Repeat of a Short Human Chemerin-Derived Peptide and Its Nontoxic d-Lysine-Containing Enantiomer Display Broad-Spectrum Antimicrobial and Antitubercular Activities

To design novel antimicrobial peptides by utilizing the sequence of the human host defense protein, chemerin, a seven-residue amphipathic stretch located in the amino acid region, 109-115, was identified, which possesses the highest density of hydrophobic and positively charged residues. Although this 7-mer peptide was inactive toward microorganisms, its 14-mer tandem repeat (Chem-KVL) was highly active against different bacteria including methicillin-resistant Staphylococcus aureus, a multidrug-resistant Staphylococcus aureus strain, and slow- and fast-growing mycobacterial species. The selective enantiomeric substitutions of its two l-lysine residues were attempted to confer cell selectivity and proteolytic stability to Chem-KVL. Chem-8dK with a d-lysine replacement in its middle (eighth position) showed the lowest hemolytic activity against human red blood cells among Chem-KVL analogues and maintained high antimicrobial properties. Chem-8dK showed in vivo efficacy against Pseudomonas aeruginosa infection in BALB/c mice and inhibited the development of resistance in this microorganism up to 30 serial passages and growth of intracellular mycobacteria in THP-1 cells.

Redox Active Antimicrobial Peptides in Controlling Growth of Microorganisms at Body Barriers

Epithelia in the skin, gut and other environmentally exposed organs display a variety of mechanisms to control microbial communities and limit potential pathogenic microbial invasion. Naturally occurring antimicrobial proteins/peptides and their synthetic derivatives (here collectively referred to as AMPs) reinforce the antimicrobial barrier function of epithelial cells. Understanding how these AMPs are functionally regulated may be important for new therapeutic approaches to combat microbial infections. Some AMPs are subject to redox-dependent regulation. This review aims to: (i) explore cysteine-based redox active AMPs in skin and intestine; (ii) discuss casual links between various redox environments of these barrier tissues and the ability of AMPs to control cutaneous and intestinal microbes; (iii) highlight how bacteria, through intrinsic mechanisms, can influence the bactericidal potential of redox-sensitive AMPs.

Expression of antimicrobial peptide genes oscillates along day/night rhythm protecting mice skin from bacteria

Antimicrobial peptides (AMPs) are important components of the innate immune system and are involved in skin protection against environmental insults and in wound healing. Herein, we assessed the gene expression of chemerin (Rarres2), cathelicidin CRAMP (Camp), and three β-defensins (Defb1, Defb3, and Defb14) in mouse skin during light/dark cycle (LD 12:12) and constant darkness (DD). Next, we examined the survival of bacteria applied on the skin at specific times during the day. We found that the expression of Rarres2, Camp, and Defb1 was the highest at 4 h after the beginning of darkness, during high activity of mice. These rhythms, however, were not maintained under DD in the skin but were present in the liver. This indicated that in the case of skin, a circadian input was masked by daily changes of light in the environment. In contrast, Defb3 and Defb14 showed the highest mRNA levels when the mice slept, and these rhythmic mRNA oscillations were maintained under DD. This shows that Rarres2, Camp, and Defb1 levels in the skin are correlated with high locomotor activity in mice and they are controlled by daily changes of light and dark. Alternatively, oscillations in the mRNA levels of Defb3 and Defb14 seem to protect skin and heal wounds during sleep. These rhythms are maintained under DD, indicating that they are regulated by a circadian clock. Our study suggests that daily AMP expression affects the survival of bacteria on the surface of skin, which depends on the phase of AMP cycling.

Bacteria Modify Their Sensitivity to Chemerin-Derived Peptides by Hindering Peptide Association With the Cell Surface and Peptide Oxidation

Chronic inflammatory skin diseases like psoriasis alter the local skin microbiome and lead to complications such as persistent infection with opportunistic/pathogenic bacteria. Disease-associated changes in microbiota may be due to downregulation of epidermal antimicrobial proteins/peptides, such as antimicrobial protein chemerin. Here, we show that chemerin and its bioactive derivatives have differential effects on the viability of different genera of cutaneous bacteria. The lethal effects of chemerin are enhanced by bacterial-derived ROS-induced chemerin peptide oxidation and suppressed by stationary phase sigma factor RpoS. Insight into the mechanisms underlying changes in the composition of cutaneous bacteria during autoreactive skin disease may provide novel ways to mobilize chemerin and its peptide derivatives for maximum antimicrobial efficacy.

Architecture of antimicrobial skin defense

The skin is the largest and the most exposed organ in the body and its defense is regulated at several anatomical levels. Here, we explore how skin layers, including the epidermis, dermis, adipose tissue, and skin appendages, as well as cutaneous microbiota, contribute to the function of skin antimicrobial defense. We highlight recent studies that reveal the differential and complementary responses of skin layers to bacterial, viral, and fungal infection. In particular, we focus on key soluble mediators in the layered skin defense, such as antimicrobial peptides, as well as on lipid antimicrobials, cytokines, chemokines, and barrier-maintaining molecules. We include our own evaluative analyses of transcriptomic datasets of human skin to map the involvement of antimicrobial peptides in skin protection under both steady state and infectious conditions. Furthermore, we explore the versatility of the mechanisms underlying skin defense by highlighting the role of the immune and nervous systems in their interaction with cutaneous microbes, and by illustrating the multifunctionality of selected antimicrobial peptides in skin protection.