The Role of Antimicrobial Peptides in
Periodontal Disease
337
peptides in the pathogenesis of inflammatory skin diseases. This example is described in
some studies related to two well-characterized skin diseases, psoriasis and atopic dermatitis.
In psoriatic lesions, expression of LL-37, hBD-2, and hBD-3 is up-regulated (Frohm et al,
1997; Harder et al, 1997a; Harder et al, 2001), whereas expression of these three peptides is
significantly reduced in atopic dermatitis lesions (Ong et al, 2002). The difference in the
levels of antimicrobial peptide expression between psoriasis and atopic dermatitis can be
elaborated by different cytokine milieus between these two skin diseases, a Th1 versus a Th2
profile, respectively (Nomura et al, 2003). It has been demonstrated that enhanced production
of IL-4 and IL-13, two cytokines categorized as a Th2 profile, in atopic dermatitis, can block
expression of some antimicrobial peptides in skin keratinocytes (Nomura et al, 2003), which
may then account for the reduction of antimicrobial peptide expression in this lesion.
It is known that one basic function of human skin is to form a natural barrier against
microbial colonization and invasion, which leads to tissue homeostasis. To further enhance
this function, the skin can also produce several antimicrobial peptides, which help control the
number and types of microorganisms on the skin. If the production of antimicrobial peptides
is impaired by dysfunction of the host immune system as a result of the pathogenesis of skin
diseases, an increased risk of opportunistic infections from bacteria or viruses in the skin
lesion ensues. Consequently, the deficiency of antimicrobial peptides, particularly LL-37, in
atopic dermatitis lesions causes frequent infections from vaccinia virus (Howell et al, 2004).
Similarly, a drastic reduction of LL-37 protein expressionthat results in increased
susceptibility to infections has also been observed in patients with acute myeloid leukemia
(An et al, 2005).
With respect to periodontal disease, data regarding the expression of
-defensin
antimicrobial peptides in different types of periodontal diseases compared to healthy
periodontal tissue are still contradictory and inconclusive. For example, the findings from one
study (Dommisch et al, 2005) showed no significant differences in
-defensin mRNA
expression in different clinical stages of periodontal disease as compared to that in normal
tissue. Nevertheless, in the same study, hBD-2 expression was found to be significantly
higher than hBD-1 expression in both gingivitis and periodontitis groups (Dommisch et al,
2005). In contrast, it was later shown in another study (Vardar-Sengul et al, 2007) that the
levels of hBD-1 expression did not significantly differ from those of hBD-2 expression in
patients with gingivitis. However, in patients with periodontitis, hBD-1 expression was
significantly higher than hBD-2 expression in chronic periodontitis, whereas hBD-2
expression was significantly higher than hBD-1 expression in aggressive periodontitis
(Vardar-Sengul et al, 2007). The reason behind these discrepancies may be due to a small
number of patients and healthy volunteers, recruited in each study. Consequently, before any
conclusions can be drawn for the relationship between
-defensin expression and periodontal
disease, a larger study is required for assessing more accurate levels of
-defensin expression
in both healthy
and diseased tissues, obtained from different types of periodontal diseases.
It is noteworthy that significant up-regulation of both hBD-1 and hBD-2 expression is
found in periodontal pocket epithelium as compared to the adjacent healthy epithelium from
the same patient (Lu et al, 2004). In contrast, higher levels of hBD-3 expression are found in
periodontally healthy tissues as compared to diseased tissues (Bissell et al, 2004). These may
suggest differential functions between hBD-1/hBD-2 and hBD-3 in periodontal disease, and
Suttichai Krisanaprakornkit and Sakornrat Khongkhunthian
338
also a more protective role for hBD-3 in regulating host immune responses to microbial
assaults, as mentioned under the previous headings.
To the best of our knowledge, there has been no report that shows the relationship
between the deficiency of
-defensin expression in periodontal tissues and periodontal
diseases. On the contrary, both LL-37, which is mainly derived from neutrophils, and
neutrophil
-defensins show a direct link to the pathogenesis of a certain type of periodontitis.
This is revealed by one study (Pütsep et al, 2002) that shows the deficiency in LL-37 and the
reduction of neutrophil
-defensins in patients with morbus Kostmann syndrome, a severe
congenital neutropenia. These patients suffer from recurrent gingivitis and even severe
periodontitis during early childhood that result from the lack of neutrophil-derived
antimicrobial peptides. Furthermore, it has been demonstrated
invitro
that several periodontal
pathogens, e.g.,
Aggregatibacter actinomycetemcomitans
, are sensitive to the bactericidal
effects of LL-37 (Tanaka et al, 2000; Isogai et al, 2003), so it is likely that the defective
antimicrobial function of neutrophils from patients with morbus Kostmann syndrome, who
are deficient in LL-37, cannot eliminate
Aggregatibacter actinomycetemcomitams
, which is
highly associated with early-onset periodontitis.
In this regard, it is interesting to further investigate whether the deficiency of these
antimicrobial peptides is also implicated with other forms of periodontitis associated with a
syndrome, for instance, juvenile periodontitis in Papillon-Lefèvre syndrome, whose
abnormalities result from cathepsin C mutations (Hart et al, 1999; Toomes et al, 1999). Is it
probable that some antimicrobial peptides are substrates for cathepsin C enzyme, and these
peptides may become more active after enzymatic degradation? If the answer is positive, one
can assume that impaired cathepsin C function may not yield sufficient amounts of active
antimicrobial peptides to exert their antimicrobial effects on periodontal pathogens. The
deficiency in active antimicrobial peptides finally leads to repeated periodontal infections.
Dostları ilə paylaş: