Effect of in vitro aging on the biosynthesis of glycosaminoglycans by human skin fibroblasts. Modulation by the elastin-laminin receptor

With Great Age Comes Great Metastatic Ability: Ovarian Cancer and the Appeal of the Aging Peritoneal Microenvironment

Age is one of the biggest risk factors for ovarian cancer. Older women have higher rates of diagnosis and death associated with the disease. In mouse models, it was shown that aged mice had greater tumor burden than their younger counterparts when intraperitoneally injected with ovarian tumor cells. While very few papers have been published looking at the direct link between ovarian cancer metastasis and age, there is a wealth of information on how age affects metastatic microenvironments. Mesothelial cells, the peritoneal extracellular matrix (ECM), fibroblasts, adipocytes and immune cells all exhibit distinct changes with age. The aged peritoneum hosts a higher number of senescent cells than its younger counterpart, in both the mesothelium and the stroma. These senescent cells promote an inflammatory profile and overexpress Matrix Metalloproteinases (MMPs), which remodel the ECM. The aged ECM is also modified by dysregulated collagen and laminin synthesis, increases in age-related crosslinking and increasing ovarian cancer invasion into the matrix. These changes contribute to a vastly different microenvironment in young and aged models for circulating ovarian cancer cells, creating a more welcoming “soil”.

Smad3 deficiency alters key structural elements of the extracellular matrix and mechanotransduction of wound closure

The loss of TGFbeta or its downstream mediator, Smad3, key players in tissue repair, accelerates closure of incisional wounds in mice. In contrast, we now report that excisional ear wounds in mice lacking Smad3 enlarge compared with wild-type controls resulting from changes in extracellular matrix molecules, which alter the mechanotransduction properties of these wounds. Specifically, levels of elastin and glycosoaminoglycans are increased, collagen fibers are more compactly organized, and matrix modulators like integrins, TGFbeta1, and matrix metalloproteinases (MMPs) are altered both basally and after wounding in Smad3 knockout mice. Mechanical testing of dorsal skin correlates these changes in matrix composition with functional parameters, specifically an increased elastic modulus, suggesting an imbalance of tissue forces. We propose that the altered mechanical elastic properties translate into a persistent retractile force that is opposed by decreased wound contractile forces contributing to the enlarging ear wound in Smad3 knockout mice. These studies highlight a previously undescribed role for Smad3 in the mechanotransduction of matrix unsupported ear wound closure.

Influence of aging on glycosaminoglycans and small leucine-rich proteoglycans production by skin fibroblasts

Skin aging is characterised by a progressive deterioration of its functional properties, linked to alterations of dermal connective tissue. Whereas many studies have been devoted to collagen alterations during aging, the situation is less clear concerning glycosaminoglycans and proteoglycans. Particularly, the alterations of the expression of small leucine-rich proteoglycans (SLRPs), a family of proteoglycans strongly implicated in cell regulation, have never been studied. In the present study we measured glycosaminoglycans and small leucine-rich proteoglycans synthesis by skin fibroblasts from donors of 1 month to 83 years old. [3H]-glucosamine and [35S]-sulfate incorporation did not show significant differences of sulfated GAG synthesis during aging. On the other hand, a significant positive correlation was found between hyaluronan secretion and donor's age. Northern blot analysis of SLRPs mRNAs showed a significant negative correlation of lumican mRNA with donor's age, whereas decorin and biglycan mRNAs were not significantly altered. Immunohistochemical study and quantitative image analysis confirmed a decreased lumican accumulation in aged human skin. Taken together, our results suggest that impairment of glycosaminoglycans and SLRPs synthesis might be involved in the functional alterations of aged skin.

Pharmacology of skin aging. Stimulation of glycosaminoglycan biosynthesis by L-fucose and fucose-rich polysaccharides, effect of in vitro aging of fibroblasts

The effect of L-fucose and fucose-rich polysaccharides (FROP-s [Biomed. Pharmacother., 2003; 57: 187-94]) was investigated, using human skin fibroblast cultures at several passages. The cells were incubated with radioactive glucosamine for 24 h, followed by the determination of individual glycosaminoglycans (GAG-s) by selective hydrolysis using specific enzymes. The effect of L-fucose and of FROP-3 [Biomed. Pharmacother., in 2003; 57: 187-94], both at 1 and 10 microg/ml, added to the culture medium, was investigated. L-Fucose stimulated the incorporation of the tracer in heparan sulfates by fibroblasts at the ninth passage by 20%. FROP-3 stimulated incorporation in keratan sulfates by 45% by fibroblasts of the fifth passage. This effect was identical at both concentrations tested. For fibroblasts at the ninth passage FROP-3 stimulated incorporation in dermatan sulfate. This effect was dose dependent of the order of +67% at 1 microg/ml and +128% at 10 microg/ml. Incorporation in hyaluronan was also stimulated by about +27%. These stimulations of GAG-biosynthesis might play a role in the increase of total skin thickness of hairless rats treated with L-fucose, as well as in several other favorable results recorded for FROP-3 such as the increased hydration (resistance to pressure) and elasticity of human skin (Robert C, Robert AM, Robert L).

Effect of L-fucose and fucose-rich polysaccharides on elastin biosynthesis, in vivo and in vitro

With increasing age elastic fibres in human skin are progressively lysed and skin elasticity is also decreasing. Still there is an age-dependent increase of elastic fibre surface density, mostly due to an alteration of the fibres. The present experiments were undertaken to explore if L-fucose and fucose-rich polysaccharides (FROP-s) could influence elastin biosynthesis. We show here, that topical application of a fucose-containing preparation to the skin of hairless rats increased after 4 weeks the elastic fibre surface density by about 40%, shown by quantitative morphology. Using human skin fibroblasts in explant cultures, the addition of L-fucose or of FROP-3 increased the biosynthesis of immunoprecipitable tropoelastin by about 40%. No increase was found however of desmosine-isodesmosine in skin explant cultures after 72 h of incubation. The effect of L-fucose and FROP-3 on the biosynthesis of collagen and non-collagen proteins excreted by the skin explant cultures was also investigated. L-fucose, but not FROP-3, decreased collagen biosynthesis but both increased non-collagen protein biosynthesis. These results show that L-fucose and FROP-3 stimulate tropoelastin biosynthesis in vitro, and elastic fibre formation in vivo. This stimulation concerns also several non-collagen proteins secreted by skin explant cultures. Elastic fibre formation necessitates the simultaneous synthesis of several microfibrillar glycoproteins as well as of tropoelastin. The increased elastic fibre density in the in vivo experiments suggests that this is indeed achieved by L-fucose and FROP-3, further demonstrating their efficiency in the control of age-dependent modifications of connective tissues in general and of skin in particular.

Pharmacological properties of fucose. Applications in age-related modifications of connective tissues

Fucose is the only component of glycoconjugates of vertebrates in the L-configuration. It exhibits a number of unique and interesting biological properties reviewed briefly in this article. Its constant end-standing position on glycan chains predisposes fucose to play a key role in cell-cell and cell-matrix interactions, mediated by several receptors such as those recognising the Lewis-type blood group substances, fucose-recognising lectines and the mannose-fucose receptors. Some of the as yet unstudied or less well understood properties of L-fucose were explored in the present study, as its non-enzymatic interaction with amine-groups on macromolecules, its cellular uptake attributed to specific transport mechanisms and its effect on fibroblast cell cultures. We could document the stimulation of cell-proliferation and the inhibition of MMP-expression and activation, both for MMP-2 and MMP-9. These and the other shortly reviewed properties of L-fucose may play an important role in its biological applications and actions.

Protection by L-fucose and fucose-rich polysaccharides against ROS-produced cell death in presence of ascorbate

It was shown previously, that millimolar concentrations of ascorbate have cytotoxic and anti-proliferative effects (Eur. J. Clin. Invest. 32 (2002) 372). With increasing concentrations of ascorbate an increasing number of fibroblasts was detached from the culture dish and shown to be lysed by the effect of ascorbate-induced generation of reactive oxygen species (ROS-s). It also could be shown, that this cytotoxic effect is partly due to the dose-dependent inhibition by ascorbate of fibronectin biosynthesis. Superoxide dismutase (SOD) and catalase were shown to salvage cells from ROS-induced cell-death by preventing the inhibition of fibronectin biosynthesis. We used this model system to test the cyto-protective effect of L-fucose and fucose-rich oligo- and polysaccharides (FROP-s). It appeared that relatively low concentrations of L-fucose and FROP-3 (Biomed. Pharmacother. in press) could efficiently protect fibroblasts from the ascorbate-induced cell-death. These novel pharmacological properties of L-fucose and FROP-3 might well be related to their accelerating effect of wound healing.

Changes related to age and cerebrovascular symptoms in the extracellular matrix of human carotid plaques

BACKGROUND AND PURPOSE

Many processes involved in the pathogenesis of atherosclerosis result in modifications of the extracellular matrix. These changes not only determine the mechanical stability of atherosclerotic lesions but can directly or indirectly influence further development of the lesions. The purpose of the present study was to compare the matrix composition of human carotid plaques from symptomatic patients with those obtained from patients without symptoms. Furthermore, matrix changes related to age were studied.

METHODS

Thirty atherosclerotic carotid plaques were removed by endarterectomy from 27 patients and divided into 2 groups on the basis of the presence of ipsilateral symptoms. The plaques were homogenized, and the total levels of the major components of the extracellular matrix were determined.

RESULTS

Plaques associated with symptoms were characterized by increased levels of elastin (1.58+/-0.46 versus 1.24+/-0.40 mg/g wet wt; P=0.03) and decreased levels of hydroxyapatite (45.1+/-46.3 versus 131.4+/-111.7 mg/g wet wt; P=0.02) compared with asymptomatic plaques. The increase in elastin in plaques from symptomatic patients was due to elevated levels of an intermediate-size fraction, as determined by liquid chromatography. Collagen and sulfated glycosaminoglycans were present in equal amounts in both groups. Elastin content in carotid plaques decreased with age.

CONCLUSIONS

Carotid plaques from symptomatic patients have lower levels of hydroxyapatite than those from asymptomatic patients. The present study also raises the possibility that non-cross-linked forms of elastin, increased in plaques associated with symptoms, could be a marker of plaque vulnerability and/or directly induce harmful cellular activities or increase lipoprotein retention in the vascular wall.

Modulation of cell-phenotype during in vitro aging. Glycosaminoglycan biosynthesis by skin fibroblasts and corneal keratocytes

The aim of this study was to compare keratocyte and fibroblast phenotypes during in vitro aging by comparing their biosynthesis of glycosaminoglycans using explant and cell cultures. Human skin and corneal explant cultures were realised with Dulbecco Modified Eagle's medium containing 3H glucosamine. Sequential cell cultures were studied at different passages for GAGs biosynthesis by 3H glucosamine incorporation followed by selective degradation with specific hydrolases. Radioactivity was determined and each GAG fraction evaluated. KS and DS are the major components synthesised by corneal explant culture. During in vitro aging, keratocytes synthesised 41% less KS between passages 4-9 with a decrease by 26% of the proportion of DS observed in the same conditions. In skin explant cultures, as expected the major components are CS and hyaluronan (HA). In the first cell passage studied compared with skin organ cultures we could notice a strong decrease of the proportions of DS and KS compensated by an increase of the proportion of HA. During the successive passages of fibroblasts, the proportions of DS and HS decreased (-30 and -62%, respectively) and those of KS increased (+90%). These results indicate that there remain measurable differences between keratocyte and fibroblast phenotypes as far as GAG-synthesis is concerned all though the successive passages, starting from explant cultures and up to the limits of in vitro cell passages.

Cellular and molecular mechanisms of aging and age related diseases

This review on aging is focused on those cellular and molecular mechanisms which concern age related pathologies. The central question addressed is the relationship between normal aging and age-related pathologies such as osteoarthritis, cardiovascular diseases, emphysema, malignant tumors and cognitive decline, dementias. The mechanisms recognized as most important in cell and tissue aging are briefly outlined. Emphasis is laid on the importance of post-synthetic modifications of the macromolecules of the extracellular matrix and on cell matrix interactions. Loss of intercellular communication and cell-matrix interactions as a result of receptor decay and receptor uncoupling were recently recognized as key events. Unavoidable poly-pathology at advanced age may be the answer to the above question.