Poly(A) tail shortening correlates with mRNA repression in tropoelastin regulation

Transcriptional and posttranscriptional mechanisms contribute to the dysregulation of elastogenesis in Schimke immuno-osseous dysplasia

BACKGROUND

Schimke immuno-osseous dysplasia (SIOD) is an autosomal recessive disorder caused by mutations in SMARCAL1. A frequent complication is arteriosclerosis associated with reduced elastin expression; however, the mechanism underlying the reduced elastin expression remains unknown.

METHODS

Expression of transcriptional regulators of elastin (ELN) and microRNA (miRNA) regulators of ELN messenger RNA (mRNA), ELN promoter methylation, and ELN mRNA poly(A) tail length were assessed by quantitative RT-PCR, bisulfite Sanger sequencing, and the Poly(A) Tail Length Assay Kit, respectively, in unaffected developing human aortae and in an SIOD aorta.

RESULTS

Comparing unaffected fetal and adult aortae, ELN precursor mRNA (pre-mRNA) levels remained nearly constant, whereas mRNA levels declined by ~10(2)-fold. This corresponded with a reduction in poly(A) tail length but not with changes in the other parameters. In contrast, compared to the unaffected fetal aortae, the SIOD aorta had 18-fold less ELN pre-mRNA and 10(4)-fold less mRNA. This corresponded with increased expression of miRNA regulators and shorter ELN mRNA poly(A) tail lengths but not with altered expression of ELN transcriptional regulators or ELN promoter methylation.

CONCLUSION

Posttranscriptional mechanisms account for the reduction in ELN mRNA levels in unaffected aortae, whereas transcriptional and posttranscriptional mechanisms reduce elastin expression in SIOD aorta and predispose to arteriosclerosis.

Oxidized low-density lipoprotein accelerates the destabilization of extracellular-superoxide dismutase mRNA during foam cell formation

Extracellular-superoxide dismutase (EC-SOD) is one of the main anti-oxidative enzymes that protect cells against the damaging effects of superoxide. In the present study, we investigated the regulation of EC-SOD expression during the oxidized low density lipoprotein (oxLDL)-induced foam cell formation of THP-1-derived macrophages. The uptake of oxLDL into THP-1-derived macrophages was increased and EC-SOD expression was decreased in a time-dependent manner by oxLDL. Furthermore, EC-SOD suppression by oxLDL was mediated by the binding to scavenger receptors, especially CD36, from the results with siRNA experience. EC-SOD expression is known to be regulated by histone acetylation and binding of the transcription factor Sp1/3 to the EC-SOD promoter region in human cell lines. However, oxLDL did not affect these processes. On the other hand, the stability of EC-SOD mRNA was decreased by oxLDL. Moreover, oxLDL promoted destabilization of ectopically expressed mRNA from EC-SOD or chimeric Cu,Zn-SOD gene with the sequence corresponding to 3'UTR of EC-SOD mRNA, whereas oxLDL had no effect on ectopic mRNA produced from EC-SOD gene lacking the sequence. These results suggested that oxLDL decreased the expression of EC-SOD, which, in turn, accelerated the destabilization of EC-SOD mRNA, leading to weaker protection against oxidative stress and atherosclerosis.

The receptor for advanced glycation end-products supports lung tissue biomechanics

The receptor for advanced glycation end-products (RAGE) and its soluble forms are predominantly expressed in lung but its physiological importance in this organ is not yet fully understood. Since RAGE acts as a cell adhesion molecule, we postulated its physiological importance in the respiratory mechanics. Respiratory function in a buffer-perfused isolated lung system and biochemical parameters of the lung were studied in young, adult, and old RAGE knockout (RAGE-KO) mice and wild-type (WT) mice. Lungs from RAGE-KO mice showed a significant increase in the dynamic lung compliance and a decrease in the maximal expiratory air flow independent of age-related changes. We also determined lower mRNA and protein levels of elastin in lung tissue of RAGE-KO mice. RAGE deficiency did not influence the collagen protein level, lung capillary permeability, and inflammatory parameters (TNF-α, high-mobility group box protein 1) in lung. Overexpressing RAGE as well as soluble RAGE in lung fibroblasts or cocultured lung epithelial cells increased the mRNA expression of elastin. Moreover, immunoprecipitation studies indicated a trans interaction of RAGE in lung epithelial cells. Our findings suggest the physiological importance of RAGE and its soluble forms in supporting the respiratory mechanics in which RAGE trans interactions and the influence on elastin expression might play an important role.

Elastomeric Recombinant Protein-based Biomaterials

Elastomeric protein-based biomaterials, produced from elastin derivatives, are widely investigated as promising tissue engineering scaffolds due to their remarkable properties including substantial extensibility, long-term stability, self-assembly, high resilience upon stretching, low energy loss, and excellent biological activity. These elastomers are processed from different sources of soluble elastin such as animal-derived soluble elastin, recombinant human tropoelastin, and elastin-like polypeptides into various forms including three dimensional (3D) porous hydrogels, elastomeric films, and fibrous electrospun scaffolds. Elastin-based biomaterials have shown great potential for the engineering of elastic tissues such as skin, lung and vasculature. In this review, the synthesis and properties of various elastin-based elastomers with their applications in tissue engineering are described.