Rapid changes in the exon/intron structure of a mammalian thrombin inhibitor gene

Heparin cofactor II attenuates vascular remodeling in humans and mice

Heparin cofactor II (HCII), a serine protease inhibitor (serpin), inactivates thrombin action in the subendothelial layer of the vascular wall. Because a congenitally HCII-deficient patient has been shown to have multiple atherosclerotic lesions, it is hypothesized that HCII plays a pivotal role in the development of vascular remodeling, including atherosclerosis. To clarify this issue, 3 clinical studies concerning plasma HCII activity and atherosclerosis were carried out, and results demonstrated that a higher incidence of in-stent restenosis after percutaneous coronary intervention, maximum carotid arterial plaque thickness, and prevalence of peripheral arterial disease occurred in subjects with low plasma HCII activity. Furthermore, HCII-deficient mice were generated by a gene targeting method to determine the mechanism of the vascular protective action of HCII. Because HCII(-/-) mice were embryonically lethal, we used HCII(+/-) mice and found that they manifested augmentation of intimal hyperplasia and increased thrombosis after cuff or wire injury to the femoral arteries. HCII(+/-) mice with vascular injury showed augmentation of inflammatory cytokines and chemokines and oxidative stress. These abnormal phenotypes of vascular remodeling observed in HCII(+/-) mice were almost restored by human HCII protein supplementation. HCII protects against vascular remodeling, including atherosclerosis, in both humans and mice, and plasma HCII activity might be a predictive biomarker and novel therapeutic target for the prevention of cardiovascular diseases.

Multiple gains of spliceosomal introns in a superfamily of vertebrate protease inhibitor genes

Background

Intron gains reportedly are very rare during evolution of vertebrates, and the mechanisms underlying their creation are largely unknown. Previous investigations have shown that, during metazoan radiation, the exon-intron patterns of serpin superfamily genes were subject to massive changes, in contrast to many other genes.

Results

Here we investigated intron dynamics in the serpin superfamily in lineages pre- and postdating the split of vertebrates. Multiple intron gains were detected in a group of ray-finned fishes, once the canonical groups of vertebrate serpins had been established. In two genes, co-occurrence of non-standard introns was observed, implying that intron gains in vertebrates may even happen concomitantly or in a rapidly consecutive manner. DNA breakage/repair processes associated with genome compaction are introduced as a novel factor potentially favoring intron gain, since all non-canonical introns were found in a lineage of ray-finned fishes that experienced genomic downsizing.

Conclusion

Multiple intron acquisitions were identified in serpin genes of a lineage of ray-finned fishes, but not in any other vertebrates, suggesting that insertion rates for introns may be episodically increased. The co-occurrence of non-standard introns within the same gene discloses the possibility that introns may be gained simultaneously. The sequences flanking the intron insertion points correspond to the proto-splice site consensus sequence MAG↑N, previously proposed to serve as intron insertion site. The association of intron gains in the serpin superfamily with a group of fishes that underwent genome compaction may indicate that DNA breakage/repair processes might foster intron birth.

Strain-dependent embryonic lethality and exaggerated vascular remodeling in heparin cofactor II-deficient mice

Heparin cofactor II (HCII) specifically inhibits thrombin action at sites of injured arterial wall, and patients with HCII deficiency exhibit advanced atherosclerosis. However, the in vivo effects and the molecular mechanism underlying the action of HCII during vascular remodeling remain elusive. To clarify the role of HCII in vascular remodeling, we generated HCII-deficient mice by gene targeting. In contrast to a previous report, HCII(-/-) mice were embryonically lethal. In HCII(+/-) mice, prominent intimal hyperplasia with increased cellular proliferation was observed after tube cuff and wire vascular injury. The number of protease-activated receptor-1-positive (PAR-1-positive) cells was increased in the thickened vascular wall of HCII(+/-) mice, suggesting enhanced thrombin action in this region. Cuff injury also increased the expression levels of inflammatory cytokines and chemokines in the vascular wall of HCII(+/-) mice. The intimal hyperplasia in HCII(+/-) mice with vascular injury was abrogated by human HCII supplementation. Furthermore, HCII deficiency caused acceleration of aortic plaque formation with increased PAR-1 expression and oxidative stress in apoE-KO mice. These results demonstrate that HCII protects against thrombin-induced remodeling of an injured vascular wall by inhibiting thrombin action and suggest that HCII is potentially therapeutic against atherosclerosis without causing coagulatory disturbance.

Vertebrate serpins: construction of a conflict-free phylogeny by combining exon-intron and diagnostic site analyses

A combination of three independent biological features, genomic organization, diagnostic amino acid sites, and rare indels, was used to elucidate the phylogeny of the vertebrate serpin (serine protease inhibitor) superfamily. A strong correlation between serpin gene families displaying (1) a conserved exon-intron pattern and (2) family-specific combinations of amino acid residues at specific sites suggests that present-day vertebrates encompass six serpin gene families which evolved from primordial genes by massive intron insertion before or during early vertebrate radiation. Introns placed at homologous positions in the gene sequences in combination with diagnostic sequence characters may also constitute a reliable kinship indicator for other protein superfamilies.