Fibrillin-2 Degradation by Matrix Metalloproteinase-2 in Periodontium

Matrix Metalloproteinases in the Periodontium-Vital in Tissue Turnover and Unfortunate in Periodontitis

The extracellular matrix (ECM) is a complex non-cellular three-dimensional macromolecular network present within all tissues and organs, forming the foundation on which cells sit, and composed of proteins (such as collagen), glycosaminoglycans, proteoglycans, minerals, and water. The ECM provides a fundamental framework for the cellular constituents of tissue and biochemical support to surrounding cells. The ECM is a highly dynamic structure that is constantly being remodeled. Matrix metalloproteinases (MMPs) are among the most important proteolytic enzymes of the ECM and are capable of degrading all ECM molecules. MMPs play a relevant role in physiological as well as pathological processes; MMPs participate in embryogenesis, morphogenesis, wound healing, and tissue remodeling, and therefore, their impaired activity may result in several problems. MMP activity is also associated with chronic inflammation, tissue breakdown, fibrosis, and cancer invasion and metastasis. The periodontium is a unique anatomical site, composed of a variety of connective tissues, created by the ECM. During periodontitis, a chronic inflammation affecting the periodontium, increased presence and activity of MMPs is observed, resulting in irreversible losses of periodontal tissues. MMP expression and activity may be controlled in various ways, one of which is the inhibition of their activity by an endogenous group of tissue inhibitors of metalloproteinases (TIMPs), as well as reversion-inducing cysteine-rich protein with Kazal motifs (RECK).

Oral Intake of Low-Molecular-Weight Collagen Peptide Improves Hydration, Elasticity, and Wrinkling in Human Skin: A Randomized, Double-Blind, Placebo-Controlled Study

Collagen-peptide supplementation could be an effective remedy to improve hydration, elasticity, and wrinkling in human skin. The aim of this study was to conduct a double-blind, randomized, placebo-controlled trial to clinically evaluate the effect on human skin hydration, wrinkling, and elasticity of Low-molecular-weight Collagen peptide (LMWCP) with a tripetide (Gly-X-Y) content >15% including 3% Gly-Pro-Hyp. Individuals (n = 64) were randomly assigned to receive either placebo or 1000 mg of LMWCP once daily for 12 weeks. Parameters of skin hydration, wrinkling, and elasticity were assessed at baseline and after 6 weeks and 12 weeks. Compared with the placebo group, skin-hydration values were significantly higher in the LMWCP group after 6 weeks and 12 weeks. After 12 weeks in the LMWCP group, visual assessment score and three parameters of skin wrinkling were significantly improved compared with the placebo group. In case of skin elasticity, one parameter out of three was significantly improved in the LMWCP group from the baseline after 12 weeks, while, compared with the placebo group, two parameters out of three in the LMWCP group were higher with significance after 12 weeks. In terms of the safety of LMWCP, none of the subjects presented adverse symptoms related to the test material during the study period. These results suggest that LMWCP can be used as a health functional food ingredient to improve human skin hydration, elasticity, and wrinkling.

Potential Role of Reversion-Inducing Cysteine-Rich Protein with Kazal Motifs (RECK) in Regulation of Matrix Metalloproteinases (MMPs) Expression in Periodontal Diseases

Periodontal diseases are characterized by pathological destruction of extracellular matrix (ECM) of periodontal tissues. Matrix metalloproteinases (MMPs) are a significant part of the degradation of ECM. However, the regulation of MMPs expression level in periodontal diseases is as yet undetermined.

RECK (reversion-inducing cysteine-rich protein with Kazal motifs), a novel membrane-anchored inhibitor of MMPs, could regulate the expressions of MMP-2, 9 and MT1-MMP as a cell surface-signaling molecule. Thus, we propose that RECK may play an important role in regulating MMPs in the ECM degradation of periodontal diseases. The RECK/MMPs signaling pathway could provide a new approach for prevention and treatment of RECK in periodontal diseases by blocking MMPs.

Microfibril-associated glycoprotein-1 controls human ciliary zonule development in vitro

The ciliary zonule in the eye, also known as Zinn’s zonule, is composed of oxytalan fibers, which are bundles of microfibrils consisting mainly of fibrillin-1. However, it is still unclear which of the microfibril-associated molecules present in the ciliary zonule controls oxytalan fibers. Microfibril-associated glycoprotein-1 (MAGP-1) is the only microfibril-associated molecule identified in the human ciliary zonule. In the present study, we used siRNA against MAGP-1 in cultures of human non-pigmented ciliary epithelial cells to examine the extracellular deposition and appearance of fibrillin-1 employing Western blotting and immunofluorescence. MAGP-1 suppression led to a reduction of fibrillin-1 deposition. Immunofluorescence also confirmed that RNAi-mediated down-regulation of MAGP-1 led to suppression of fiber development. These results suggest that MAGP-1 plays a crucial role in the extracellular deposition of fibrillin-1 during formation of the human ciliary zonule.

Latent transforming growth factor-β binding protein 2 negatively regulates coalescence of oxytalan fibers induced by stretching stress

Oxytalan fibers are extracellular matrix components consisting of pure microfibrils. However, the mechanism whereby oxytalan fibers develop is not fully understood. We have previously reported that in human periodontal ligament (PDL) fibroblasts subjected to stretching stress, bundles of oxytalan fibers coalesce under the control of fibulin-5. Latent transforming growth factor-β binding protein 2 (LTBP-2) is known to bind to fibulin-5. The purpose of this study was to clarify the role of LTBP-2 in the coalescence of oxytalan fibers. We subjected PDL fibroblasts to stretching in order to examine the effects of LTBP-2 on the coalescence of oxytalan fibers in cell/matrix layers. Interaction of LTBP-2 with fibulin-5 was examined by immunoprecipitation assay, and changes in LTBP-2 deposition upon stretching were investigated by Western blotting and immunofluorescence assays. We used small interfering RNA against LTBP-2 in PDL cell culture and examined the appearance of oxytalan fibers on the basis of immunofluorescence. Stretching induced coalescence of oxytalan fibers, but did not affect LTBP-2 expression. The amount of extracellularly deposited LTBP-2 was decreased by about 70% as a result of stretching, compared with the control. LTBP-2 interacted with fibulin-5 on the fibers, and stretching decreased the amount of the LTBP-2 interacted with fibulin-5 by about 60%. Oxytalan fiber coalescence did not occur when LTBP-2 was suppressed by about 95%, whereas it occurred when LTBP-2 was suppressed by about 40%, fibulin-5 being colocalized with oxytalan fibers. These results suggest that LTBP-2, in response to tension stress, may negatively control the function of fibulin-5, thereby modulating the mechanism of oxytalan fiber coalescence.

Development of the oxytalan fiber system in the rat molar periodontal ligament evaluated by light- and electron-microscopic analyses

In the elastic fiber system of the periodontal ligaments only oxytalan fibers can be identified, whereas all three types of fibers, oxytalan, elaunin and elastic fibers, are present in the gingiva. However, little information is available concerning their organization in the developing periodontal ligament. In the present study, growth and distribution of the oxytalan fiber system were examined in the developing periodontal ligament of rat molars using the specific staining for oxytalan, elastic and collagen fibers, and electron-microscopic analyses. Oxytalan staining clearly confirmed the earliest oxytalan fibers in a bell-staged tooth germ at embryonic day 18, which were tiny violet-colored fibers in the dental follicle. Their cross images were made up of dot-like microfibrils of 10-15nm in diameter close to fibroblasts in the dental follicle of the rat molars aged 1 day. These microfibrils appeared to be linked to one another through delicate filaments in 3-nm-diameter. At the beginning of root formation, the cross figures of oxytalan fibers were found as dot-like structures around the root sheath as well as in areas very close to blood vessels. As development proceeded, longer oxytalan fibers were produced in the apico-occlusal direction along with blood vessels. In addition, the immunoreactive products to anti-amyloid β protein on the surface of blood vessels suggest that this molecule might be involved in the adhesion of oxytalan fibers to vascular basement membranes. Thus, the oxytalan fiber system might regulate periodontal ligament function through tensional variations registered on the walls of the vascular structures.

Fibrillin-1 and fibrillin-2 are essential for formation of thick oxytalan fibers in human nonpigmented ciliary epithelial cells in vitro

The ciliary zonule, also known as Zinn's zonule, is composed of oxytalan fibers. However, the mechanism by which epithelial cells in the ciliary body form these fibers in not fully understood. We examined human nonpigmented ciliary epithelial cells to determine the appearance and amount of oxytalan fibers in terms of positivity for their major components, fibrillin-1 and fibrillin-2. Examination of fibrillin-1 and fibrillin-2 expression by immunofluorescence revealed that thin fibers positive for fibrillin-1 on Day 2 changed to thick fibers by Day 8. The fibers positive for fibrillin-2 appeared on the thick fibrillin-1-positive fibers after Day 4. Northern blot analysis revealed that the level of fibrillin-1 did not change markedly, while induction of fibrillin-2 gene was evident on Day 5. Western blot analysis showed that fibrillin-1 deposition increased gradually, while that of fibrillin-2 increased markedly from Day 5 to Day 8. Fibrillin-1 suppression did not lead to the formation of fibrillin-2-positive thick fibers, whereas fibrillin-2 suppression led to the formation of fibrillin-1-positive thin fibers, but not thick fibers. These results suggest that both fibrillin-1 and fibrillin-2 are essential for the formation of thick oxytalan fibers in the ciliary zonule and are informative for clarifying the mechanism of homeostasis of the ocular matrix.

Fibulin-4 and -5, but not Fibulin-2, are Associated with Tropoelastin Deposition in Elastin-Producing Cell Culture

Elastic system fibers consist of microfibrils and tropoelastin. During development, microfibrils act as a template on which tropoelastin is deposited. Fibrillin-1 is the major component of microfibrils. It is not clear whether elastic fiber-associated molecules, such as fibulins, contribute to tropoelastin deposition. Among the fibulin family, fibulin-2, -4 and -5 are capable of binding to tropoelastin and fibrillin-1. In the present study, we used the RNA interference (RNAi) technique to establish individual gene-specific knockdown of fibulin-2, -4 and -5 in elastin-producing cells (human gingival fibroblasts; HGF). We then examined the extracellular deposition of tropoelastin using immunofluorescence. RNAi-mediated down-regulation of fibulin-4 and -5 was responsible for the diminution of tropoelastin deposition. Suppression of fibulin-5 appeared to inhibit the formation of fibrillin-1 microfibrils, while that of fibulin-4 did not. Similar results to those for HGF were obtained with human dermal fibroblasts. These results suggest that fibulin-4 and -5 may be associated in different ways with the extracellular deposition of tropoelastin during elastic fiber formation in elastin-producing cells in culture.

Tissue elasticity and the ageing elastic fibre

The ability of elastic tissues to deform under physiological forces and to subsequently release stored energy to drive passive recoil is vital to the function of many dynamic tissues. Within vertebrates, elastic fibres allow arteries and lungs to expand and contract, thus controlling variations in blood pressure and returning the pulmonary system to a resting state. Elastic fibres are composite structures composed of a cross-linked elastin core and an outer layer of fibrillin microfibrils. These two components perform distinct roles; elastin stores energy and drives passive recoil, whilst fibrillin microfibrils direct elastogenesis, mediate cell signalling, maintain tissue homeostasis via TGFβ sequestration and potentially act to reinforce the elastic fibre. In many tissues reduced elasticity, as a result of compromised elastic fibre function, becomes increasingly prevalent with age and contributes significantly to the burden of human morbidity and mortality. This review considers how the unique molecular structure, tissue distribution and longevity of elastic fibres pre-disposes these abundant extracellular matrix structures to the accumulation of damage in ageing dermal, pulmonary and vascular tissues. As compromised elasticity is a common feature of ageing dynamic tissues, the development of strategies to prevent, limit or reverse this loss of function will play a key role in reducing age-related morbidity and mortality.

Fibulin-5 contributes to microfibril assembly in human periodontal ligament cells

The elastic system fibers comprise oxytalan, elaunin and elastic fibers, which differ in their relative microfibril and elastin content. Human periodontal ligaments (PDL) contain only oxytalan fibers (pure microfibrils) among them. Since fibulin-5 regulates the organization of elastic fibers to link the fibers to cells, we hypothesized that fibulin-5 may contribute to the formation of oxytalan fibers. We used siRNA for fibulin-5 in PDL cell culture to examine the extracellular deposition of fibrillin-1 and -2, which are the major components of microfibrils. Fibulin-5 was labeled on microfibrils positive for fibrillin-1 and -2. Fibulin-5 suppression reduced the level of fibrillin-1 and -2 deposition to 60% of the control level. These results suggest that fibulin-5 may control the formation of oxytalan fibers, and play a role in the homeostasis of oxytalan fibers.

Integrin alphavbeta3 regulates microfibril assembly in human periodontal ligament cells

Fibrillin-1 is the major structural component of extracellular microfibrils. However, the mechanism by which extracellular fibrillin-1 assembles into microfibrils is not fully understood. Fibrillin-1 contains the Arg-Gly-Asp (RGD) motif, which may allow binding to RGD-recognizing integrins. We hypothesized that integrin alphavbeta3 on the cell surface of human periodontal ligament (PDL) fibroblasts may influence fibrillin-1 assembly into cell/matrix layers. We treated PDL fibroblasts with an integrin alphavbeta3-specific antagonist to examine fibrillin-1 assembly. Western blotting and immunofluorescence analysis showed that treatment with the integrin alphavbeta3 antagonist at 5 muM clearly abolished fibrillin-1 deposition. These results provide for the first time evidence that integrin alphavbeta3 regulates extracellular assembly of fibrillin-1, thereby modulating cell-mediated homeostasis of microfibrils.