Regulation of elastin synthesis in organ and cell culture

Regulation of elastin synthesis in pathological states

Elastin is rapidly deposited during late gestation in resilient tissues such as the arteries, lungs and skin owing to increased concentration of its mRNA. Pathological states can arise from congenital insufficiency or disorganization of elastin (cutis laxa). Other elastin deficiencies may be due to excess elastolysis or gene dosage effects. In the former, high turnover rates can be assessed by measurements of elastin degradation products in urine. Excess elastin accumulation by skin fibroblasts is characteristic of genetic diseases such as Buschke-Ollendorff syndrome, Hutchinson-Gilford progeria and keloid. Elastin expression is modulated by peptide growth factors, steroid hormones and phorbol esters, among which transforming growth factor beta (TGF-beta) is an especially potent up-regulator, acting largely through stabilization of mRNA. Recent evidence indicates cutis laxa fibroblasts that express little or no elastin have normal transcriptional activity but abnormal rates of elastin mRNA degradation. This defect is substantially reversed by TGF-beta through mRNA stabilization. Current studies explore the hypothesis that stability determinants lie within the 3' untranslated region of elastin mRNA. Post-transcriptional control of elastin expression appears to be a major regulatory mechanism.

Quantitative Analysis for Soluble Elastin in Circulation and Cell Culture Fluids Using Monoclonal Antibody‐Based Sandwich Immunoassay

We have newly established 3 distinct murine monoclonal antibodies (MoAbs) against human soluble elastin by using chemically denatured immunogen isolated from human aorta; they are designated as HASG-2, HASG-30, and HASG-61-1. All of these MoAbs were highly reactive with soluble forms of native elastin in normal human serum. HASG-2 and HASG-61-1 MoAbs can recognize soluble bovine elastin as well as human antigen, but HASG-30 cannot. The sandwich enzyme-linked immunosorbent assay (ELISA) for human soluble elastin was developed with HASG-61-1 labeled with peroxidase and HASG-30 immobilized on the microplates. The circulating levels of soluble elastin in human healthy subjects (mean +/- SD; 42.9 +/- 19.9ng/mL; n = 85) could be measured with full accuracy and reproducibility, and gradually increased with aging. The positive correlation between the levels and ages was statistically significant (r = 0.581, p < 0.0001). In addition, we could also determine the concentration of tropoelastin secreted from cultured human dermal fibroblasts accurately by this ELISA. This simple assay can be utilized for the routine clinical laboratory screening of patients with arteriosclerotic vascular diseases or to accurately determine the concentrations of tropoelastin secreted from cultured human cells.

Cellular ageing related proteins secreted by human fibroblasts

Fibroblast secreted proteins participate in the formation of extracellular matrix. Extracellular matrix affects growth factor action, mediates cell adhesion and supports cell growth. Structural and quantitative characteristics of secreted proteins are modified in a similar manner, during both in vivo and in vitro cellular ageing. Such ageing related modifications may either be directly controlled by primary ageing causes, or evolve from a reformation of the extracellular matrix induced by a few ageing defects in key proteins such as fibronectin. They may result in the further inhibition of cell adhesion, cell stimulation by growth factors and, eventually, of cell proliferative ability.

Increased elastin production by progeria skin fibroblasts is controlled by the steady-state levels of elastin mRNA

Hutchinson-Gilford progeria is a unique, rare disease with markedly accelerated aging. The average lifespan of affected individuals is 12 years. Although the biochemical basis of the syndrome is unknown, its influence appears to be primarily upon mesodermal tissues. Characteristics such as the altered appearance of the skin and the extensive and fatal involvement of the cardiovascular system led us to study elastin production in cultured skin fibroblasts from three progeroid individuals. We found tropoelastin production by progeroid cells was elevated six- to nine-fold at the protein and mRNA levels, while relative collagen synthesis was similar to control strains. There was little difference between progeroid and normal cells in expression of total protein or in total cellular mRNA content. Western blot analysis of tropoelastin from progeroid fibroblasts confirmed increased production of elastin but revealed no gross changes in the molecular mass. The significant increase in tropoelastin expression lends support to the concept that progeria results from a mesenchymal dysplasia, and offers a possible biochemical marker for the phenotype.