Genetic causes of aortic aneurysms. Unlearning at least part of what the textbooks say

Extracellular matrix dynamics in vascular remodeling

Vascular remodeling is the adaptive response to various physiological and pathophysiological alterations that are closely related to aging and vascular diseases. Understanding the mechanistic regulation of vascular remodeling may be favorable for discovering potential therapeutic targets and strategies. The extracellular matrix (ECM), including matrix proteins and their degradative metalloproteases, serves as the main component of the microenvironment and exhibits dynamic changes during vascular remodeling. This process involves mainly the altered composition of matrix proteins, metalloprotease-mediated degradation, posttranslational modification of ECM proteins, and altered topographical features of the ECM. To date, adequate studies have demonstrated that ECM dynamics also play a critical role in vascular remodeling in various diseases. Here, we review these related studies, summarize how ECM dynamics control vascular remodeling, and further indicate potential diagnostic biomarkers and therapeutic targets in the ECM for corresponding vascular diseases.

The mechanical impact of col11a2 loss on joints; col11a2 mutant zebrafish show changes to joint development and function, which leads to early-onset osteoarthritis

Collagen is the major structural component of cartilage, and mutations in the genes encoding type XI collagen are associated with severe skeletal dysplasias (fibrochondrogenesis and Stickler syndrome) and early-onset osteoarthritis (OA). The impact of the lack of type XI collagen on cell behaviour and mechanical performance during skeleton development is unknown. We studied a zebrafish mutant for col11a2 and evaluated cartilage, bone development and mechanical properties to address this. We show that in col11a2 mutants, type II collagen is made but is prematurely degraded in maturing cartilage and ectopically expressed in the joint. These changes are correlated with increased stiffness of both bone and cartilage; quantified using atomic force microscopy. In the mutants, the skeletal rudiment terminal region in the jaw joint is broader and the interzone smaller. These differences in shape and material properties impact on joint function and mechanical performance, which we modelled using finite element analyses. Finally, we show that col11a2 heterozygous carriers reach adulthood but show signs of severe early-onset OA. Taken together, our data demonstrate a key role for type XI collagen in maintaining the properties of cartilage matrix; which when lost leads to alterations to cell behaviour that give rise to joint pathologies.This article is part of the Theo Murphy meeting issue 'Mechanics of development'.

Abdominal aortic aneurysm and histological, clinical, radiological correlation

To date, the pathogenesis of abdominal aortic aneurism (AAA) still remains unclear. As such, the aim of this study was to evaluate changes of the aortic structure during AAA. We analysed the microscopic frame of vessels sections, starting from the primum movens leading to abnormal dilatation. AAA samples were collected and processed through various staining methods (Verhoeff-Van Gieson, Masson Goldner, Sirius Red). Subsequently, the vessel morphology and collagenic web of the tunica media and adventitia were determined and the amount of type I and type III collagen was measured. We also applied immune-histochemistry markers for CD34 and PGP 9.5 in order to identify vascular and nerve structures in the aorta. Immune-positivity quantification was used to calculate the percentage of the stained area. We found increasing deposition of type I collagen and reduced type III collagen in both tunica media and adventitia of AAA. The total amount of vasa vasorum, marked with CD34, and nerva vasorum, marked with PGP 9.5, was also higher in AAA samples. Cardiovascular risk factors (blood pressure, dyslipidemia, cigarette smoking) and radiological data (maximum aneurism diameter, intra-luminal thrombus, aortic wall calcification) increased these changes. These results suggest that the tunica adventitia may have a central role in the pathogenesis of AAA as clearly there are major changes characterized by rooted inflammatory infiltration. The presence of immune components could explain these modifications within the framework of the aorta.

Role of Collagen Gene Polymorphisms in the Structure of Early Gestation Loss

Studies of collagen gene polymorphisms associated with predisposition to early recurrent miscarriages revealed significant differences in the distribution of COL1A1 C-1997A C>A (rs1107946) genotypes and alleles in the group of pregnant patients with early miscarriages in comparison with controls (normal pregnancy). Identification of COL1A1 C-1997A C>A (rs1107946) collagen gene polymorphisms at the stage of pregnancy planning will make it possible to form early miscarriage risk groups for more thorough preparation to gestation and optimization of follow up of this patient population.

The role of lysyl oxidase family members in the stabilization of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a major cause of morbidity and mortality in the United States today. We employed a model for AAA development using apolipoprotein E knock out mice fed a high-fat diet and treated with ANG II and β-aminopropionitrile (β-APN) for 4 wk. ANG II induces hypertension and atherosclerotic disease, whereas β-APN inhibits the activity of the lysyl oxidase/ lysyl oxidase-like protein (LOX/LOXL) family members. LOX/LOXL family members crosslink collagen and elastin in the extracellular matrix and therefore contribute to the integrity and stabilization of a healthy vessel wall. In this model, cotreatment with ANG II and β-APN caused a 90% AAA incidence and increased atherosclerotic lesion formation from less than 5% to greater than 25% after 4 wk. In more atheroprotected mouse strains (C57BL/6 and BalbC), cotreatment with ANG II and β-APN caused 50% and 40% AAA incidence, respectively. These data demonstrate the importance of LOX/LOXL to the stability of the vessel wall. Therapeutic strategies to overexpress LOX/LOXL enzymes or to support the crosslinking of soluble matrix proteins in a polymeric scaffold are a promising opportunity to achieve stabilization of AAAs.

Group B streptococcus mycotic aneurysm of the abdominal aorta: report of a case and review of the literature

Mycotic aneurysm of the aorta is an uncommon condition, and Group B Streptococcus (GBS) is exceedingly rare in this setting. We present the first reported case of a GBS-infected abdominal aortic aneurysm (AAA) in North America. Key clinical and imaging findings and pathologic correlation are highlighted. A relevant review of the literature is discussed, which will bring the reader up to date with this specific disease entity.

A case of multiple giant coronary aneurysms and abdominal aortic aneurysm coexisting with IgG4-related disease

IgG4-related disease (IgG4RD) is a unique systemic lymphoproliferative disorder characterized by elevated serum IgG4 levels and IgG4-producing plasma cell expansion in the affected tissues, which are accompanied by fibrotic or sclerotic changes. Vascular lesions may also be a part of IgG4RD as a number of case reports have discussed inflammatory abdominal aortic aneurysms associated with IgG4RD, but coronary artery lesions seem to be rare complications of IgG4RD. A 71-year-old man suffered from multiple giant coronary aneurysms and an abdominal aortic aneurysm with concurrent pancreatic, gall bladder, bile duct, and salivary gland lesions resulting from IgG4RD. The present observations suggest that coronary aneurysms may also develop as a consequence of this disease.

Structural and Functional Genetic Disorders of the Great Vessels and Outflow Tracts

Development of the aorta and pulmonary artery is a complex process involving multiple molecular genetic pathways that modulate morphogenesis of the outflow tracts and the anastomosis of branch vessels. Recent genetic studies of the cardiovascular system demonstrate that congenital and adult onset progressive disorders of the great vessels such as aneurysms are components of generalized vascular, cardiac, and extracardiovascular syndromes. Current paradigms suggest that aortic disease is founded in patterning anomalies of the conotruncus that occur in utero. These aberrations can be consequences of genetic aberrations in transcriptional regulation of signal transduction both within and outside the developing great vessels.

Ruptured abdominal aortic aneurysm in a 12-month-old boy

A rare case of abdominal aortic aneurysm in a 12-month-old boy is reported. The clinical presentation was one of acute catastrophic rupture. The morphologic and histologic findings suggested an idiopathic etiology.

Genetic influences on aortic root size in American Indians: the Strong Heart Study

Aortic root dilatation is a major pathophysiological mechanism for aortic regurgitation and predisposes the aortic root to dissection or rupture. However, only a small proportion of the variance of aortic root size can be explained by its known clinical and demographic correlates. The present study was undertaken to determine the heritability of echocardiographically derived aortic root diameter in the American Indian participants in the second Strong Heart Study examination. Echocardiograms were analyzed in 1373 SHS participants who had > or =1 family member in the cohort. Heritability calculations were performed by using variance component analysis as implemented in SOLAR, a computer analysis program. In a polygenic model, the variables entered and identified as covariates of larger aortic root diameter were older age, male sex, and center (P<0.001), which accounted for 35% of the overall variability of aortic root diameter. After simultaneous adjustment was made for these significant covariates, the proportion of phenotypic variance due to additive genetic contribution or residual heritability (h2) was 0.51 (SE=0.08, P<0.001). Additionally, simultaneous adjustment for height, weight, and systolic and diastolic BPs yielded slightly lower residual h2 of aortic root diameter (h2=0.44, SE=0.08, P<0.001), which accounted for 26% of the overall variance of aortic root size. Because center effects were identified as significant covariates in the analyses, h2 analyses were performed separately in Arizona, Oklahoma, and North/South Dakota centers, which confirmed that a significant proportion of the phenotypic variance of aortic root diameter is due to additive genetic contribution. Heredity explains a substantial proportion of the variability of aortic root size that is not accounted for by age, sex, body size, and blood pressure. Echocardiographic screening of family members with aortic root dilatation may identify other individuals predisposed to aortic dissection or rupture.

Identification of a Chromosome 11q23.2-q24 Locus for Familial Aortic Aneurysm Disease, a Genetically Heterogeneous Disorder

Background —Aortic aneurysms cause significant mortality, and >20% relate to hereditary disorders. Familial aortic aneurysm (FAA) has been described in such conditions as the Marfan and Ehlers-Danlos type IV syndromes, due to defects in the fibrillin-1 and type III procollagen genes, respectively. Other gene defects that cause isolated aneurysms, however, have not thus far been described.

Methods and Results —We studied 3 families affected by FAA. No family met the diagnostic criteria for either Marfan or Ehlers-Danlos syndrome. Echocardiography defined involvement of both the thoracic and abdominal aorta. In family ANA, candidate gene analysis excluded linkage to loci associated with aneurysm formation, including fibrillin-1 , fibrillin-2 , and type III procollagen , and chromosome 3p24.2-p25. Genome-wide linkage analysis identified a 2.3-cM FAA locus ( FAA1 ) on chromosome 11q23.3-q24 with a maximum multipoint logarithm of the odds score of 4.4. In family ANB, FAA was linked to fibrillin-1 . In family ANF, however, FAA was not linked to any locus previously associated with aneurysm formation, including fibrillin-1 and FAA1 .

Conclusions —FAA disease is genetically heterogeneous. We have identified a novel FAA locus at chromosome 11q23.3-q24, a critical step toward elucidating 1 gene defect responsible for aortic dilatation. Future characterization of the FAA1 gene will enhance our ability to achieve presymptomatic diagnosis of aortic aneurysms and will define molecular mechanisms to target therapeutics.

Ehlers-Danlos syndrome type IV and multiple aortic aneurysms--a case report

Beside atherosclerosis, aortic aneurysms can be part of the clinical spectrum of many systemic diseases, including infectious, inflammatory, genetic and, less often, congenital disorders. A 48-year-old white man presented with multiple large aneurysms of the aorta and its main branches. Medical history was unremarkable except for the presence of a softened abdominal mass since he was 28 years old. On the physical examination, an arterial murmur was heard over the left carotid artery and a palpable mass was noted in the whole right side of the abdomen. No skin or joint abnormalities were noted. Aortography, computed tomography, and magnetic resonance angiography showed multiple large aneurysms of the descending thoracic and abdominal aorta. Aneurysms of the innominate, left subclavian, and carotid arteries were also seen. This case resembles those previously reported, in which multiple aortic aneurysms were associated with abnormalities of the type III procollagen gene (COL3A1). Although the classic stigmas of the Ehlers-Danlos syndrome type IV were lacking, this genetic disease may be the cause of the multiple aneurysms in this patient.

Aortic dissection

The presentation of aortic dissection in the emergency department may be more subtle than the classic description of a shocked patient with "ripping" chest pain. The epidemiology, variation in presentation, investigation, and management of aortic dissection are reviewed.

The role of type III collagen in the development of familial abdominal aortic aneurysms

OBJECTIVES

to evaluate the prevalence of familiar abdominal aortic aneurysm (AAA) and the role of type III collagen deficiency.

METHODS

fifty-six consecutive patients coming for aneurysm repair were asked if one or more first-degree relatives had an AAA. During operation, a skin biopsy was taken from the patients for protein analysis to measure the type III collagen production in cultured fibroblasts.

RESULTS

a positive family history was found in 28.6% of the AAA patients. Six (10.7%) of the AAA patients had a type III collagen deficiency (mean 4.3% (S.D.+/-0.5)). In this group three men, mean age 65.3 years (S.D.+/-5.0), had a positive family history and a type III collagen deficiency. Segregation analysis with an intragenic marker in the type III collagen gene in a single family was in favour of linkage with the gene for type III procollagen (COL3A1) locus.

CONCLUSIONS

the high prevalence of familial AAA suggests a genetic aetiology. A small group of patients have a type III collagen deficiency. Linkage with the COL3A1 gene could not be proven or excluded in the families studied.

Expression and localization of macrophage elastase (matrix metalloproteinase-12) in abdominal aortic aneurysms

Elastolytic matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of abdominal aortic aneurysms (AAA), a disorder characterized by chronic aortic wall inflammation and destruction of medial elastin. The purpose of this study was to determine if human macrophage elastase (HME; MMP-12) might participate in this disease. By reverse transcription-polymerase chain reaction, HME mRNA was consistently demonstrated in AAA and atherosclerotic occlusive disease (AOD) tissues (six of six), but in only one of six normal aortas. Immunoreactive proteins corresponding to proHME and two products of extracellular processing were present in seven of seven AAA tissue extracts. Total HME recovered from AAA tissue was sevenfold greater than normal aorta (P < 0.001), and the extracted enzyme exhibited activity in vitro. Production of HME was demonstrated in the media of AAA tissues by in situ hybridization and immunohistochemistry, but HME was not detected within the media of normal or AOD specimens. Importantly, immunoreactive HME was specifically localized to residual elastin fragments within the media of AAA tissue, particularly areas adjacent to nondilated normal aorta. In vitro, the fraction of MMP-12 sequestered by insoluble elastin was two- to fivefold greater than other elastases found in AAA tissue. Therefore, HME is prominently expressed by aneurysm-infiltrating macrophages within the degenerating aortic media of AAA, where it is also bound to residual elastic fiber fragments. Because elastin represents a critical component of aortic wall structure and a matrix substrate for metalloelastases, HME may have a direct and singular role in the pathogenesis of aortic aneurysms.

Abdominal aortic aneurysm in a young child: a 25-year follow-up study

Although abdominal aortic aneurysm (AAA) is a common problem in elderly patients, AAA is rare in children. Despite its rarity, early diagnosis is imperative to prevent limb-threatening or fatal complications. The treatment may be complicated, because it must allow for the growth of the child. A saccular AAA in an 11-year-old boy, complicated by three repeated embolizations to the lower extremities and treated by aneurysmorrhaphy 25 years ago, was studied. In addition, the long-term function of a vein interposition graft in the common femoral artery was identified.

Epidemiology and potential for prevention of abdominal aortic aneurysm

BACKGROUND

Ruptured abdominal aortic aneurysm (AAA) is a common cause of death which is preventable by elective repair of an asymptomatic AAA.

METHODS

The literature was reviewed with emphasis on epidemiological studies and population-based screening surveys.

RESULTS AND CONCLUSION

The prevalence of small AAA ranges between 3 and 8 per cent. The incidence of asymptomatic AAA seems to be increasing, although exact incidence estimates vary. The most important risk factors for AAA are male sex, age, family history and smoking. Hypertension is associated with a mildly increased risk, but diabetes is not associated with any increase. Primary prevention of AAA is not a realistic option. There is no evidence of an effective medical treatment to prevent growth of small AAAs, although trials with propranolol are under way. The only intervention to prevent death from aneurysm is elective repair of the asymptomatic lesion. Screening for asymptomatic AAA can reduce the incidence of rupture. However, further studies are needed to determine the cost effectiveness of screening compared with that of other health programmes.

Influence of hypercholesterolemia and adventitial inflammation on the development of aortic aneurysm in rabbits

Abdominal aortic aneurysms are characterized by intimal atherosclerosis, disruption and attenuation of the elastic media, and a variable adventitial inflammatory infiltrate. We have developed an animal model of this disorder to evaluate the contribution of hypercholesterolemia, medial injury, and adventitial inflammation to aneurysmal dilatation. To accomplish this, we used periaortic application of calcium chloride, which induced both medial injury with calcification and endothelial injury. Ultrasonography was used to demonstrate the dilatation and thickening of the aortic wall. Over the first 3 weeks after periaortic application of 0.25 mol/L CaCl2, the external aortic diameter increased from 3.5 +/- 0.5 to 4.2 +/- 0.8 mm, but the ID remained unchanged. This apparent wall thickening was accompanied by vascular remodeling, and biochemical changes included approximately 50% reduction in tissue hydroxyproline concentration and increased activity of gelatinases (matrix metalloproteinase [MMP]-2 and MMP-9). Independently, cholesterol feeding to induce hypercholesterolemia or the concomitant periaortic application of thioglycollate had little effect on the histological, biochemical, or diameter changes. Together, hypercholesterolemia and thioglycollate were associated with rapid aortic dilatation in CaCl2, treated animals but not controls: after 3 weeks, the ID and OD had doubled, the OD increasing from 3.5 +/- 0.4 to 7.1 +/- 0.4 mm, P = .005. The remarkable feature that accompanied this dilatation was the infiltration of cells, mostly foamy macrophages, into the adventitia, with a further reduction in hydroxyproline concentration. Adventitial inflammation may provide the critical stimulus to dilatation of an aorta with preexisting intimal and medial injury.

Abdominal aortic aneurysms in children

Abdominal aortic aneurysms are rare in children. Causes include mycotic aneurysms, vasculitides (eg, Takayasu's arteritis), connective tissue diseases (eg, Marfan's syndrome, Ehlers-Danlos syndrome, and tuberous sclerosis) and traumatic false aneurysms. Four cases are described. Case 1 was a 12-year-old boy who presented with an acute unheralded rupture of the subdiaphragmatic aorta accompanied by lower limb paralysis and ischemia. Attempted repair failed because of extensive friability of the large arteries. Histological evaluation confirmed cystic medial necrosis despite Marfanoid phenotype. Cases 2 and 3 were boys aged 12 and 11 with Takayasu's arteritis who presented with hypertensive encephalopathy and heart failure. Although both had involvement of the origins of the renal arteries, one aneurysm was predominantly suprarenal and the other infrarenal. Currently both children are being managed successfully with antihypertensive therapy. Case 4 was a 5-year-old girl who presented with hypertension and a pulsatile abdominal mass after treatment of infective endocarditis 18 months previously. Arteriography and three-dimensional computed tomography confirmed an aneurysm (6 x 5 x 4 cm) arising from the aorta and involving the right renal artery. Aneurysmectomy, removal of a small ischemic right kidney, and Gore-Tex grafting resulted in cure of the hypertension and uneventful recovery. The present series confirms that rupture is a fatal complication, renovascular complications are common, and medical control of hypertension is an essential part of management. Management strategies need to be highly individualized, and may be successful without surgical intervention. Close clinical and ultrasound follow-up of those managed nonoperatively is essential.

Interaction between fibrillin genotype and blood pressure and the development of aneurysmal disease

Debate as to whether abdominal aortic aneurysms (AAA) are caused by atherosclerosis or whether they have a strong genetic etiology continues. We have investigated the hypothesis that risk factors are likely to be strongest in patients with generalized aneurysmal disease. We screened 232 consecutive AAA patients for popliteal aneurysm and investigated cardiovascular and genetic risk factors in these patients. Ultrasonography demonstrated the presence of a popliteal aneurysm in 24 of 232 (10%) patients. Multivariate analysis identified four independent factors associated with popliteal aneurysm: age (p = 0.013), height (p = 0.017), triglyceride concentration (p = 0.009), and systolic blood pressure (p = 0.037). In the AAA patients a significant association of fibrillin-1 genotype was present, determined by a tandem repeat polymorphism, with both systolic and pulse pressure. The genotypes associated with the highest pressures were significantly more common among the patients with popliteal aneurysm, p = 0.03. Following these findings we investigated whether there was an association between fibrillin-1 genotype and blood pressure in a healthy population, 245 men aged 50-61 years. Again we found a significant association between fibrillin genotype and pulse pressure, p = 0.003. We suggest that a strong interaction occurs between fibrillin genotype and blood pressure which contributes to the development of aneurysmal disease.

Molecular genetic insights into cardiovascular disease

The recent application of molecular genetic tools to inherited forms of cardiovascular disease has provided important insight into the molecular mechanisms underlying cardiac arrhythmias, cardiomyopathies, and vascular diseases. These studies point to defects in ion channels, contractile proteins, structural proteins, and signaling molecules as key players in disease pathogenesis. Genetic testing is now available for a subset of inherited cardiovascular diseases, and new mechanism-based therapies may be available in the near future. This remarkable progress and the implications it may have for more common forms of cardiovascular disease are reviewed here.

A Gly1127Ser mutation in an EGF-like domain of the fibrillin-1 gene is a risk factor for ascending aortic aneurysm and dissection

Ascending aortic disease, ranging from mild aortic root enlargement to aneurysm and/or dissection, has been identified in 10 individuals of a kindred, none of whom had classical Marfan syndrome (MFS). Single-strand conformation analysis of the entire fibrillin-1 (FBN1) cDNA of an affected family member revealed a G-to-A transition at nucleotide 3379, predicting a Gly1127Ser substitution. The glycine in this position is highly conserved in EGF-like domains of FBN1 and other proteins. This mutation was present in 9 of 10 affected family members and in 1 young unaffected member but was not found in other unaffected members, in 168 chromosomes from normal controls, and in 188 chromosomes from other individuals with MFS or related phenotypes. FBN1 intragenic marker haplotypes ruled out the possibility that the other allele played a significant role in modulating the phenotype in this family. Pulse-chase studies revealed normal fibrillin synthesis but reduced fibrillin deposition into the extracellular matrix in cultured fibroblasts from a Gly1127Ser carrier. We postulate that the Gly1127Ser FBN1 mutation is responsible for reduced matrix deposition. We suggest that mutations such as this one may disrupt EGF-like domain folding less drastically than do substitutions of cysteine or of other amino acids important for calcium-binding that cause classical MFS. The Gly1127Ser mutation, therefore, produces a mild form of autosomal dominantly inherited weakness of elastic tissue, which predisposes to ascending aortic aneurysm and dissection later in life.

The perivascular connective matrix

The functional properties of the perivascular matrix facilitate the movement, protection and the nutrition of the blood vessels. At the same time the matrix deliniates the vessels to the organs. Different vascular diseases of the vascular system implicate the perivascular matrix consisting of a network of structural and cellular connective tissue components. Impairment of its structural integrity predominantly occurs either from primary or secondary affections. Monospecific antibodies directed against different structural proteins enable detailed histomorphological examinations of the inflammatory tissue reaction in the perivascular space. Since myofibroblasts, fibrocytes, endothelial cells, and macrophages participate in tissue repair mechanisms, in vitro studies on the collagen synthesis may contribute to the understanding of the perivascular tissue reaction according to injury. The present report summarizes perivascular diseases and the in vitro synthesis of procollagen, collagen, and fibronectin of endothelial cells, fibroblasts, smooth muscle cells, and macrophages.

Pathogenesis of abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm involves many factors acting over time. However, destruction of elastin in the aortic wall is a key event that shifts the load produced by blood pressure on to collagen. This is exacerbated in the presence of hypertension. Smoking and age are further important factors, as is the site; elastic lamellae are relatively less common in the abdominal aorta. Once the shielding effect of elastin is lost, further dilatation and rupture of the aorta depend on the physical properties of the collagen present.

Synthesis of recombinant human procollagen II in a stably transfected tumour cell line (HT1080)

Apparently because the biosynthetic pathways involve eight or more highly specific post-translational enzymes, it has been difficult to obtain expression of genes for fibrillar collagens in recombinant systems. Here two constructs of the human gene for procollagen II (COL2A1) were prepared, one with about 0.5 kb of a promoter for a procollagen I gene (COL1A1) and the other with about 4 kb of the promoter for the procollagen II gene. The constructs, together with a neomycin-resistant gene, were transfected into a human tumour cell line (HT1080) that synthesizes the collagen IV found in basement membranes, but does not synthesize any fibrillar collagen. About two per 100 clones resistant to the neomycin analogue G418 synthesized and secreted human procollagen II. Milligram quantities of the recombinant procollagen II were readily isolated from the cultured medium. The recombinant procollagen II had the expected amino acid sequence as defined by nucleotide sequencing of mRNA-derived cDNA and the expected amino acid composition as defined by analysis of procollagen II that was converted into collagen II by digestion with procollagen N- and C-proteinases. Also, analysis of the carbohydrate content indicated that there was glycosylation of some of the hydroxylysine residues but no evidence of post-translational overmodification of the residues. In addition, the protein was shown to have a native conformation as assayed by a series of protease digestions. No essential differences were found between clones transfected with the COL2A1 gene construct containing the COL1A1 promoter and the similar construct containing the COL2A1 promoter in terms of number of clones synthesizing recombinant procollagen II and the levels of expression. With both constructs, the expression of the COL2A1 gene was closely related to copy number. The results demonstrated therefore that it is not essential to use a promoter for a gene normally expressed in a host cell in order to obtain gene copy-number-dependent expression of an exogenous collagen gene in stably transfected cells.

Mutations in type 1 procollagen that cause osteogenesis imperfecta: effects of the mutations on the assembly of collagen into fibrils, the basis of phenotypic variations, and potential antisense therapies

Work by a large number of investigators over the last decade has established that over 90% of patients with osteogenesis imperfecta have mutations in one of the two genes for type I procollagen, that most unrelated probands have different mutations in the genes, and that the mutations found in most of the serious variants of the disease cause synthesis of abnormal pro alpha chains of the protein. The results have demonstrated that synthesis of structurally abnormal but partially functional pro alpha chains can interfere with folding of the central region of the protein into a triple-helical conformation, prevent processing of the N-terminal propeptides of procollagen, or produce subtle alterations in conformation that interfere with the self-assembly of the protein into collagen fibrils. One of the unsolved mysteries about the disease is why some mutations produce severe phenotypes, whereas very similar mutations produce mild phenotypes. Recent studies in transgenic mice suggest that nongenetic factors, such as stochastic events during development, may determine the severity of the disease phenotype produced by a specific mutation. Also, recent results raised the possibility that strategies of antisense gene therapy may be effective in treating the disease some time in the future. Specific inhibition of expression of a mutated collagen gene has been obtained with antisense oligonucleotides in cell culture experiments. However, there is no means of selective delivery of antisense oligonucleotides to the appropriate tissues.

A disorder of collagen biosynthesis in patients with cerebral artery aneurysm

12 patients with subarachnoid hemorrhage due to rupture of a cerebral aneurysm were examined clinically for symptoms and signs of a connective tissue disorder and biochemically for details of the biosynthesis of collagen. No uniform clinical pattern of any connective tissue disorder was seen in these patients, although selected signs were observed. Skin fibroblast cultures were then established. The rate of procollagen production in two cell lines was reduced by 40% and 50%, respectively, and the intracellular accumulation of hydroxy[14C]proline (as a percentage of total hydroxy[14C]proline) was increased by 70% in each relative to eight control cell lines. No difference was found in the degree of intracellular degradation of procollagen. After pulse-labelling, however, the radioactive procollagen was secreted into the medium in 1 h in the control cells, but required at least 3 h in the two aneurysm patient cell lines. The results, thus, suggest that delayed secretion of procollagen rather than increased intracellular degradation led to the reduction in the rate of procollagen synthesis in these two fibroblast lines from patients with cerebral artery aneurysm.

Content and turnover of extracellular matrix protein in human "nonspecific" and inflammatory abdominal aortic aneurysms

Inflammatory aneurysms (IAs) have peculiar macroscopic and histological aspects which make them very different from nonspecific aneurysms (NSAs). These morphological differences seem to be determined by significant modifications of the extracellular matrix. Extracellular matrix protein component concentrations were determined biochemically in infrarenal aortic biopsies from 10 NSAs, five IAs and five non-aneurysmal aortic controls. The concentration of each wall component was expressed in % w/w (relative concentration) and in mg/wall longitudinal cm (absolute concentration) with reference to total protein recovered after hydrolysis and amino acid analysis. The biochemical results were correlated with the histological and ultrastructural features of the specimens. A significant increase in total collagen was observed in the two groups of aneurysms, with respect to the controls (NSA = 285%, IA = 382%). In contrast the 80-90% decrease in the relative concentration of elastin observed in both types of aneurysm was less marked (NSA = 55%, IA = 39%). This fall was not significant when expressed in mg/cm, although elastin derived peptide (EDP) levels in the plasma of these patients was significantly higher than in age-matched controls. The concentration of the soluble collagen fraction appeared significantly higher (Mann-Whitney, p < 0.05) in the IAs with respect to the NSAs, whilst no differences were observed between the two groups regarding the concentration of insoluble elastin and of wall and plasma EDPs. As well as providing evidence of increased elastin turnover, this study emphasises the conspicuous modifications of collagen deposition in the wall of abdominal aortic aneurysms which appeared more marked in the inflammatory group.(ABSTRACT TRUNCATED AT 250 WORDS)

An inbred line of transgenic mice expressing an internally deleted gene for type II procollagen (COL2A1). Young mice have a variable phenotype of a chondrodysplasia and older mice have osteoarthritic changes in joints

Studies were carried out on a line of transgenic mice that expressed an internally deleted COL2A1 gene and developed a phenotype resembling human chondrodysplasias (Vandenberg et al. 1991. Proc. Natl. Acad. Sci. USA. 88:7640-7644. Marked differences in phenotype were observed with propagation of the mutated gene in an inbred strain of mice in that approximately 15% of the transgenic mice had a cleft palate and a lethal phenotype, whereas the remaining mice were difficult to distinguish from normal littermates. 1-d- and 3-mo-old transgenic mice that were viable showed microscopic signs of chondrodysplasia with reduced amounts of collagen fibrils in the cartilage matrix, dilatation of the rough surfaced endoplasmic reticulum in the chondrocytes, and decrease of optical path difference in polarized light microscopy. The transgenic mice also showed signs of disturbed growth as evidenced by lower body weight, lower length and weight of the femur, decreased bone collagen, decreased bone mineral, and decreased resistance of bone to breakage. Comparisons of mice ranging in age from 1 d to 15 mo demonstrated that there was decreasing evidence of a chondrodysplasia as the mice grew older. Instead, the most striking feature in the 15-mo-old mice were degenerative changes of articular cartilage similar to osteoarthritis.

Sequencing of cDNA from 50 unrelated patients reveals that mutations in the triple-helical domain of type III procollagen are an infrequent cause of aortic aneurysms

Detailed DNA sequencing of the triple-helical domain of type III procollagen was carried out on cDNA prepared from 54 patients with aortic aneurysms. The 43 male and 11 female patients originated from 50 different families and five different nationalities. 43 patients had at least one additional blood relative who had aneurysms. Five overlapping asymmetric PCR products, covering all the coding sequences of the triple-helical domain of type III procollagen, were sequenced with 28 specific sequencing primers. Analysis of the sequencing gels revealed only two nucleotide changes that altered the structure of the protein. One was a substitution of threonine for proline at amino acid position 501 and its functional importance was not clearly established. The other was a substitution of arginine for an obligatory glycine at amino acid position 136. In 40 of the 54 patients, detection of a polymorphism in the mRNA established that both alleles were expressed. The results indicate that mutations in type III procollagen are the cause of only about 2% of aortic aneurysms.

Collagens and their abnormalities in a wide spectrum of diseases

Collagens are a family of extracellular matrix proteins that play a dominant role in maintaining the structural integrity of various tissues. Nineteen collagen types containing altogether more than 30 distinct polypeptide chains have now been identified, and their genes have been found to be dispersed among at least 12 chromosomes. Mutations in collagen genes or deficiencies in the activities of specific post-translational enzymes of collagen synthesis have been characterized in many heritable disorders such as osteogenesis imperfecta, several chondrodysplasias, several subtypes of the Ehlers-Danlos syndrome, the X-linked Alport syndrome and dystrophic forms of epidermolysis bullosa. In addition, collagen mutations have been found in certain common diseases, namely osteoporosis, osteoarthrosis and aortic aneurysms, and it is now evident that subsets of patients with these diseases have defects in types I, II or III collagen, respectively, as a predisposing factor. Mutations have so far been identified in only six of the more than 30 collagen genes, and thus research into collagen defects is only in its early stages. Transgenic mice have been shown to offer an excellent tool for investigating the consequences of mutations in collagen genes and identifying additional diseases caused by collagen defects. Excessive collagen accumulation also poses a common problem in medicine, leading to fibrosis with impairment of the normal functioning of the affected tissue. This has prompted attempts to develop drugs which inhibit collagen synthesis. Prolyl 4-hydroxylase would seem a particularly suitable target for antifibrotic therapy, and several compounds are now known that inhibit this enzyme. In particular, derivatives of pyridine 2,4-dicarboxylate have been shown to inhibit hepatic collagen accumulation in rats with two models of liver fibrosis.

Selection for screening for familial aortic aneurysms

The reported familial clustering of abdominal aortic aneurysm (AAA) indicates the possible rewards of family-based screening programmes with respect both to the number of asymptomatic aneurysms detected and to identifying associated genes. Ultrasonographic screening of 28 families (25 brothers and 28 sisters) was carried out together with collecting a history and a blood sample for analysis of the cholesterol level and genetic markers. Among the screened siblings six (11 per cent), all > 60 years old, had an AAA > or = 3.0 cm in diameter. A further 11 siblings (21 per cent), six of whom were < 60 years old, had a wide (2.5-2.9 cm) aorta. The presence of an aneurysmal or wide aorta was significantly associated with smoking (P = 0.027), male sex (P = 0.008) and a proband age of < 60 years (P = 0.031). Polymorphic genetic markers for type III collagen and haptoglobin were not informative in these families. These results indicate that the efficiency of screening siblings of patients with AAA could be improved by limiting it to brothers with a smoking history and/or siblings of younger patients. The familial component appears to be greatest in these younger patients.