Modifications of fibronectin in age-related diseases: diabetes and cancer

Association of TATA box-binding protein-associated factor RNA polymerase I subunit C (TAF1C) with T2DM

Proteins differential expression in type 2 diabetes mellitus (T2DM) can be due to etiological factors or pathological changes, such proteins can be utilized as biomarkers. Identification of a marker protein out of thousands became a feasible task during the proteomics era by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, blood samples were obtained from 80 Bahraini subjects with and without T2DM, a subset was used for proteomic analysis by LC-MS/MS, while all samples were used for ELISA analysis of 3 proteins, TATA-box binding protein-associated factor RNA polymerase-1-C (TAF1C), ceruloplasmin (CERP) and fibronectin (FN). The former 2 proteins were selected from the T2DM-protein-panel identified by LC-MS/MS, and the latter was analyzed for validation of the setting. The main findings of the proteomic analysis are i. Identifications of 62 differentially expressed proteins in T2DM, ii. Upregulation of 71% of the identified proteins. While the ELISA analysis showed that; both TAF1C and FN were significantly increased in T2DM (P0.015 and P0.001, respectively), while CERP was not (P0.088). Logistic regression analysis: i. confirmed the above associations after correction for covariates, ii. Revealed an interaction between age and gender that affect the association of the proteins with T2DM. In conclusion, knowing that TAF1C is a prerequisite in ribosomal biogenesis, our ELISA results are suggestive of increased protein synthesis in T2DM, explaining the observed upregulation of the proteins identified by LC-MSMS. The association between T2DM and TAF1C is a novel finding that might open a new avenue in DM research.

Age associated communication between cells and matrix: a potential impact on stem cell-based tissue regeneration strategies

A recent paper demonstrated that decellularized extracellular matrix (DECM) deposited by synovium-derived stem cells (SDSCs), especially from fetal donors, could rejuvenate human adult SDSCs in both proliferation and chondrogenic potential, in which expanded cells and corresponding culture substrate (such as DECM) were found to share a mutual reaction in both elasticity and protein profiles (see ref. (1) ). It seems that young DECM may assist in the development of culture strategies that optimize proliferation and maintain "stemness" of mesenchymal stem cells (MSCs), helping to overcome one of the primary difficulties in MSC-based regenerative therapies. In this paper, the effects of age on the proliferative capacity and differentiation potential of MSCs are reviewed, along with the ability of DECM from young cells to rejuvenate old cells. In an effort to highlight some of the potential molecular mechanisms responsible for this phenomenon, we discuss age-related changes to extracellular matrix (ECM)'s physical properties and chemical composition.

CVD risk factors are related to plasma fibrin clot properties independent of total and or γ' fibrinogen concentration

INTRODUCTION

Cardiovascular disease (CVD) risk factors are associated with total fibrinogen concentration and/or altered clot structure. It is however, unclear whether such associations with clot structure are ascribed to fibrinogen concentration or other independent mechanisms. We aimed to determine whether CVD risk factors associated with increased total and/or γ' fibrinogen concentration, were also associated with altered fibrin clot properties and secondly whether such associations were due to the fibrinogen concentration or through independent associations.

MATERIALS AND METHODS

In a plasma setting CVD risk factors (including total and γ' fibrinogen concentration) were cross-sectionally analysed in 2010 apparently healthy black South African participants. Kinetics of clot formation (lag time, slope and maximum absorbance) as well as clot lysis times were calculated from turbidity curves.

RESULTS

Of the measured CVD risk factors age, metabolic syndrome, C-reactive protein (CRP), high density lipoprotein (HDL)-cholesterol and homocysteine were significantly associated with altered fibrin clot properties after adjustment for total and or γ' fibrinogen concentration. Aging was associated with thicker fibres (p=0.004) while both metabolic syndrome and low HDL-cholesterol levels were associated with lower rates of lateral aggregation (slope), (p=0.0004 and p=0.0009), and the formation of thinner fibres (p=0.007 and p=0.0004). Elevated CRP was associated with increased rates of lateral aggregation (p=0.002) and consequently thicker fibres (p<0.0001). Hyperhomocysteinemia was associated with increased rates of lateral aggregation (p=0.0007) without affecting fibre thickness.

CONCLUSION

Final clot structure may contribute to increased CVD risk in vivo through associations with other CVD risk factors independent from total or γ' fibrinogen concentration.

Downregulation of fibronectin overexpression reduces basement membrane thickening and vascular lesions in retinas of galactose-fed rats

Overexpression of extracellular matrix (ECM) components is closely associated with the development of vascular basement membrane (BM) thickening, a histological hallmark of diabetic microangiopathy. To determine whether BM thickening of retinal capillaries could be prevented by down regulating synthesis of fibronectin, an ECM component, we used antisense oligos targeted against translation initiation site of the fibronectin transcript in galactose-fed rat, an animal model of diabetic retinopathy. After 2 months of galactose-feeding, intravitreal administration of 3 micro mol/l antisense fibronectin oligos was initiated at monthly intervals for 3 months. The antisense strategy significantly reduced fibronectin mRNA and protein level in the retinas of treated eyes compared with untreated eyes of galactose-fed rats (130 +/- 16 vs. 179 +/- 18% of control, P < 0.01, and 144 +/- 28 vs. 204 +/- 22% of control, respectively, r = 0.9) and resulted in partial reduction of retinal capillary BM width (123 +/- 16 vs. 201 +/- 12 nm, P < 0.03). In eyes treated with antisense fibronectin oligos, approximately 35% reduction in both pericyte loss and acellular retinal capillaries was observed (P < 0.04 and P < 0.03, respectively). Glycohemoglobin level was consistently elevated in the treated (6.9 +/- 0.6%) and untreated (6.5 +/- 0.7%) galactose-fed rats compared with control rats (4.5 +/- 0.8%). Overall, these results indicate that downregulation of fibronectin synthesis reduces BM thickening in retinal capillaries with beneficial effect to retinal lesions. The antisense fibronectin oligos may provide a useful approach for reducing vascular lesions in diabetic retinopathy. The thickened vascular BM may be a potential therapeutic target for preventing retinal lesions in diabetic retinopathy.

Plasma fibronectin in French centenarians

Plasma fibronectin was shown to increase with age, the difference between individuals (the SD of the mean) also increases with age. Fibronectin is highly sensitive to proteolytic degradation and several of the degradation products were shown to have noxious effects as proper proteolytic activity, activation of IL-1 and collagenase expression and also activation of fibronectin biosynthesis. It was therefore interesting to compare the plasma fibronectin values of centenarians in relatively good health with an elderly population in a geriatric hospital, somewhat younger (70-96 years) but with a variety of pathologies. A third population of men and women between 59 and 70 in good health (the EVA-epidemiological study) was also used for comparison. Plasma fibronectin was determined by a specific and highly sensitive Elisa assay. Fibronectin fragments were characterized by immunoblot. It could be shown that plasma fibronectin in centenarians had a lower distribution with lower average values than the geriatric population. Fibronectin fragments could be demonstrated in the plasma of a selection of geriatric patents but not in the plasma of centenarians. These results suggest a more moderate increase of plasma fibronectin in the relatively healthy centenarians as compared to a younger but pathological population. They also show that the plasma fibronectin of the investigated centenarians was better protected from proteolytic degradation than in the geriatric population. The above results also confirm the contention that epigenetic mechanisms such as an age-dependent increase of fibronectin synthesis and degradation and the potential noxious effects of degradation products may well play an important role in the age-dependent decline of physiological functions.

Identification of multiple genes in bovine retinal pericytes altered by exposure to elevated levels of glucose by using mRNA differential display

Loss of capillary pericytes, a characteristic finding in diabetic retinopathy, is strongly associated with hyperglycemia. The pathologic aberrations associated with diabetic retinopathy are localized primarily in the retinal capillaries and are only poorly reversed by subsequent euglycemic control. Since hyperglycemia significantly inhibits pericyte growth in culture, we investigated the regulation of gene expression in retinal pericytes exposed to physiologic (5.5mM) and pathologic (20 mM) glucose concentrations. By utilizing modifications of the mRNA differential display technique, over 14,000 mRNA species were screened, and 35 candidate clones were obtained. Partial DNA sequence demonstrated that 25 of these were distinct genes, including 7 known, 16 previously unreported, and 2 sequences with known homologues. Northern blot analysis demonstrated altered gene expression in 10 (40%), undetectable signals in 12 (48%), and nonregulation in 3 (12%). Genes with glucose-regulated expression included those encoding fibronectin (51% +/- 15%, P = 0.003; mean percentage of control +/- SD), caldesmon (68% +/- 18%; P = 0.026), two ribosomal proteins (201% +/- 72%, P = 0.011; 136% +/- 16%, P = 0.036), Rieske FeS reductase (66% +/- 17%; P = 0.029), three previously unreported sequences (57%, 167%, 271%), and molecules homologous to autoantigens (213%) and tyrosine kinases (down 16- to 33-fold). Caldesmon protein concentrations in pericytes and smooth muscle cells demonstrated decreases by Western blot analysis concordant with mRNA levels. These studies identify genes whose expression is significantly altered after 7 days of exposure to elevated glucose levels and provide new targets for understanding the adverse effects of hyperglycemia on vascular cells. In addition, this study provides strong support for the use of differential mRNA display as a method to rapidly isolate differentially expressed genes in metabolic systems.

Fibronectin and glycosaminoglycan synthesis by fibrotic pig fibroblasts in primary culture

Synthesis of fibronectin and glycosamingoglycans (GAGs) was studied in fibroblasts from pigs with post-irradiation subcutaneous fibrosis. Fibrosis was developed in the femoral muscle by local gamma irradiation with a dose of 60 Gy. Normal fibroblasts were obtained from the healthy skin of the same animal. To measure GAG and fibronectin synthesis fibrotic and normal fibroblasts were labeled with 3H-glucosamine, 35S-sulfate and 35S-methionine. Fibrotic fibroblasts synthesized 2.5 times as much fibronectin as normal skin fibroblasts but total protein synthesis did not change. Parallel enhanced secretion of hyaluronic acid and dermatan sulfate into the cell culture medium were also observed. GAGs from the pericellular layer of trypsin-digested fibrotic fibroblasts exhibited increased 3H incorporation, but reduced 35S-sulfate incorporation. The largest reduction in the latter was observed for heparan sulfate. These results indicate that the fibroblasts from the well developed fibrotic tissue maintain enhanced synthesis of matrix macromolecules in primary cultures. Structural and/or metabolic changes in secreted GAGs, combined with the stimulation of tissue repair by growth factors may be responsible for the excessive deposition of collagen in post-irradiation fibrosis.

Massive cardiac disease in a patient with Waldenstrom's macroglobulinaemia

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Aging of the extracellular matrix and its pathology

Recent concepts on the mechanisms of aging of extracellular matrix (EM) are reviewed as well as its involvement in age-associated diseases. Cell differentiation, histogenesis and organogenesis can be analyzed in terms of the program of the biosynthesis of EM macromolecules during development, maturation and aging. The most important biological role of EM is the integration of cells in tissues, of tissues in organs and of organs in the whole organism. EM can directly influence cell behavior through the contact between EM and the genome mediated by structural glycoproteins (fibronectin, laminin, elastonectin, etc.) interacting with other EM macromolecules (collagen, proteoglycans, elastin) and the cytoskeleton by trans-membrane receptors (integrins). Most age-associated diseases exhibit a deviation (qualitative or quantitative) from the normal program of EM biosynthesis. Three examples are analyzed in some detail: atherosclerosis, diabetes and malignant tumors. The degradation of elastic fibers catalyzed by cellular elastase-type enzymes is observed in atherosclerosis and also in emphysema and skin aging. Several of these enzymes were isolated and characterized from platelets, fibroblasts, smooth muscle cells and lipoproteins. The biosynthesis of some of them increases with age and facilitates cell migration. Plasma fibronectin increases with age exponentially. This increase is absent or strongly attenuated in diabetes and some cancers. Tissue fibronectin increases in diabetes, Werner syndrome and in the peritumoral desmoplastic reaction while most tumor cells can no more retain fibronectin on their membrane facilitating their movement in the organism. These examples demonstrate the importance of the study of cell matrix interactions for gerontology.

Increased biosynthesis and processing of fibronectin in fibroblasts from diabetic mice

Diabetic connective tissues exhibit a deranged regulation of extracellular matrix biosynthesis. Fibronectin is shown to be increased in human dermal connective tissue by immunofluorescence, mainly at the dermoepidermal and capillary basement membranes. The rate of fibronectin biosynthesis, excretion, and incorporation in a pericellular polymeric form was investigated using genetically diabetic KK mouse skin and fibroblasts as compared to Swiss and C57BL mouse skin and fibroblasts. The rate of incorporation of [35S]methionine into proteins recovered in the culture medium or in deoxycholate and NaDodSO4 or urea extracts was investigated. The rate of incorporation in the medium and deoxycholate extracts was comparable. However, the relative rate of incorporation of the tracer in the NaDodSO4-extractable, pericellular polymeric form was increased in the diabetic KK fibroblasts both for total proteins and for fibronectin. In pulse-chase experiments, the deoxycholate-soluble and NaDodSO4-soluble fractions exhibited a precursor-product relationship. The rate of passage of fibronectin from the deoxycholate-soluble (cellular compartment) form to the NaDodSO4-soluble (pericellular polymeric) form was strongly accelerated in the diabetic fibroblast cultures. These results confirm the increased rate of synthesis of fibronectin in diabetic fibroblasts as well as its processing from the cellular compartment to the polymeric pericellular form. The increase of fibronectin in diabetic connective tissues, in the matrix as well as in the basement membranes, may play a role in the mechanism of micro- and macroangiopathies and in the perturbed permeability characteristics of the diabetic capillaries, and as a glycoprotein it may contribute to the increased periodic acid/Schiff reagent staining of diabetic capillary basement membranes.