Low Molecular Weight Hyaluronic Acid Increases the Self-Defense of Skin Epithelium by Induction of β-Defensin 2 via TLR2 and TLR4

Abstract

In sites of inflammation or tissue injury, hyaluronic acid (HA), ubiquitous in the extracellular matrix, is broken down into low m.w. HA (LMW-HA) fragments that have been reported to activate immunocompetent cells. We found that LMW-HA induces activation of keratinocytes, which respond by producing β-defensin 2. This production is mediated by TLR2 and TLR4 activation and involves a c-Fos-mediated, protein kinase C-dependent signaling pathway. LMW-HA-induced activation of keratinocytes seems not to be accompanied by an inflammatory response, because no production of IL-8, TNF-α, IL-1β, or IL-6 was observed. Ex vivo and in vivo treatments of murine skin with LMW-HA showed a release of mouse β-defensin 2 in all layers of the epidermal compartment. Therefore, the breakdown of extracellular matrix components, for example after injury, stimulates keratinocytes to release β-defensin 2, which protects cutaneous tissue at a time when it is particularly vulnerable to infection. In addition, our observation might be important to open new perspectives in the development of possible topical products containing LMW-HA to improve the release of β-defensins by keratinocytes, thus ameliorating the self-defense of the skin for the protection of cutaneous tissue from infection by microorganisms.

Specific-sized Hyaluronan Fragments Promote Expression of Human β-Defensin 2 in Intestinal Epithelium

“…The effect of intermediate-sized HA on intestinal epithelium appears to be divergent from its effect on skin keratinocytes grown in vitro (35) in that no significant change in secreted H␤D2 protein concentration is observed in HT-29 cells following treatment with 35-kDa HA (Fig. 1E).…”

“…1E). Although defensins are best characterized as secreted effector molecules of innate defense (5), intracellular expression of H␤D2 protein has been suggested by positive immunostaining of mucosal tissue (7,14,52,53) and epithelial cell cultures (13,35) for some time. The function of intracellular H␤D2 peptide has not been studied extensively, particularly in epithelium.…”

“…Intraperitoneal injection of a polydispersed HA preparation of less than 750 kDa suppresses the epithelium-damaging, proinflammatory effects of DSS-induced murine colitis through a TLR4-dependent mechanism (34). Additionally, intermediate molecular mass HA (Ͻ200 kDa), but not high molecular mass HA (Ͼ1,000 kDa) promotes the expression of H␤D2 peptide in human keratinocytes partially through interaction with TLR4 without the accompanying inflammatory cytokine response elicited by LPS (35). Thus, endogenous HA may act as a signal to increase innate epithelial defense without provocation of the potentially damaging proinflammatory mechanisms of immune cells.…”

Human β-defensin 2 expression in ELBW infants with severe necrotizing enterocolitis

“…Mortality rate of severe NEC was 66% (n = 4) with no further deaths in the remaining patients. A total of 732 fecal samples were available (mean 11 per individual, range [5][6][7][8][9][10][11][12][13][14].…”

“…Under physiological conditions, hBD1 is expressed constitutively by intestinal epithelial cells, whereas hBD2 expression was found to be induced during infection and inflammation. hBD2 exhibits potent bactericidal activity against Gram-negative bacteria and eukaryotic pathogens, such as Candida strains (8), and reduced expression has been observed previously in preterm infants as compared with full-term babies (9); the expression of hBD2 is partly dependent on Toll-like receptor 4 (TLR4) (10), which is mainly stimulated by lipopolysaccharide (LPS), the glycolipid component of the outer membrane of Gramnegative bacteria. For correct function of TLR4, in vivo binding of MD2, a 20-30-kD glycoprotein secreted by endothelial and epithelial cells to its extracellular domain, is essential (11).…”