ATHEROMATOSIS OF THE BRAIN-SUPPLYING ARTERIES: CIRCLE OF WILLIS, BASILAR, VERTEBRAL AND THEIR BRANCHES

PURPOSE

Atherosclerotic plaques in the brain-supplying arteries are slowly-developing alterations of vascular structures that can lead to neurological impairment due to stenosis and insufficient oxygenation of eloquent brain areas. The aim of this study is to provide detailed demographic information related to the incidence of atherosclerotic plaques in the cerebral arteries.

MATERIAL AND METHODS

Forty-eight circles of Willis (21 men, 21 women, mean age: 70.26, six samples unknown) were macroscopically analyzed for length, diameter, and presence of atherosclerotic plaques. Statistical analysis was used to identify potential differences in the locations and frequencies of atherosclerotic plaques in relation to age and sex.

RESULTS

The study sample revealed 261 atherosclerotic plaques. The key findings were significant correlations between plaque development and age and between plaque location and age; however, there was no significant sex difference.

CONCLUSION

The upper and lower branches of the middle cerebral artery (MCA) were novel locations predisposing to plaque development. A cut-off value at 60 years revealed a significant difference in plaque development and distribution. There were no significant sex differences in the occurrence of atherosclerotic plaques.

The fifth head of quadriceps femoris: for sure?

PURPOSE

The quadriceps femoris has been described as a muscle composed by four heads: rectus femoris, vastus lateralis, vastus medialis and vastus intermedius. Each head fuse with the other ones making up the quadriceps tendon, which inserts into the patella. Nevertheless, there has been described a fifth component of the quadriceps muscle in recent anatomical publications. Understanding this fifth head may be important for orthopedics and radiologist.

METHODS

Cadaveric dissection of left thigh of a female 83 years old was performed to demonstrate a fifth head of the quadriceps femoris muscle.

RESULTS

In this study, a fifth head of the quadriceps femoris muscle was found in the left thigh of a female cadaver 83 years old. This fifth head was made up by four independent muscular fascicles attaching in a common flat tendon that joins distally with the lateral border of the quadriceps tendon. The fifth head found was supplied by branches of the ascending branch of the lateral femoral circumflex artery and by branches of the deep lateral division of the femoral nerve.

CONCLUSIONS

The incidence of this fifth belly in cadaveric studies has been reported as a range from 29 to 100%. However, no published articles refer an anatomical finding such as this multi-bellied fifth head. The knowledge of the existence and location of the fifth belly is necessary to make accurate diagnosis of QF muscle strains. Its anatomical course may be involved in patellar tracking.

Stimulation of nitric oxide production in rat lung lavage cells by anti-Mac-1beta antibody: effects of ozone inhalation

Acute inhalation of the pulmonary irritant ozone is associated with an inflammatory response characterized by increased numbers of macrophages in the lung that release elevated quantities of nitric oxide. The accumulation of phagocytes in the lung is dependent on expression of leukocyte adhesion molecules including Mac-1. In the present studies, we determined whether activation of the Mac-1 receptor is involved in regulating nitric oxide production by lung phagocytes, and whether this response is modified following acute ozone inhalation. Cells were isolated from the lung by bronchoalveolar lavage 48 h after exposure of female Sprague-Dawley rats to air or ozone (2 parts per million, for 3 h). Anti-Mac-1beta antibody, but not anti-Mac-1alpha antibody, stimulated nitric oxide production by cells from both air- and ozone-exposed animals. Cells from ozone-exposed rats produced more nitric oxide and expressed greater quantities of inducible nitric oxide synthase mRNA than did cells from air-exposed animals. Production of nitric oxide in response to anti-Mac-1beta was also found to be augmented by cross-linking of the Mac-1beta receptor. Pretreatment of lavage cells with granulocyte/macrophage colony-stimulating factor (GM-CSF), which activates phagocytes, enhanced the expression of Mac-1beta and increased anti-Mac-1beta-induced nitric oxide production by the cells. Lavage cells from ozone-exposed animals were more responsive to GM-CSF than were cells from control animals. Taken together, these data suggest that the Mac-1beta adhesion molecule may contribute to phagocyte activation and mediator release during ozone-induced inflammatory reactions in the lung.

Phosphorylation of the Goodpasture antigen by type A protein kinases

Collagen IV is the major component of basement membranes. The human alpha 3 chain of collagen IV contains an antigenic domain called the Goodpasture antigen that is the target for the circulating immunopathogenic antibodies present in patients with Goodpasture syndrome. Characteristically, the gene region encoding the Goodpasture antigen generates multiple alternative products that retain the antigen amino-terminal region with a five-residue motif (KRGDS). The serine therein appears to be the major in vitro cAMP-dependent protein kinase phosphorylation site in the isolated antigen and can be phosphorylated in vitro by two protein kinases of approximately 50 and 41 kDa associated with human kidney plasma membrane, suggesting that it can also be phosphorylated in vivo. Consistent with this, the Goodpasture antigen is isolated from human kidney in phosphorylated and non-phosphorylated forms and only the non-phosphorylated form is susceptible to phosphorylation in vitro. Since this motif is exclusive to the human alpha 3(IV) chain and includes the RGD cell adhesion motif, its phosphorylation might play a role in pathogenesis and influence cell attachment to basement membrane.

Characterization and expression of multiple alternatively spliced transcripts of the Goodpasture antigen gene region. Goodpasture antibodies recognize recombinant proteins representing the autoantigen and one of its alternative forms

Collagen IV, the major component of basement membranes, is composed of six distinct alpha chains (alpha 1-alpha 6). Atypically among the collagen IV genes, the exons encoding the carboxyl-terminal region of the human alpha 3(IV) chain undergo alternative splicing. This region has been designated as the Goodpasture antigen because of its reactivity in the kidney and lung with the pathogenic autoantibodies causing Goodpasture syndrome. The data presented in this report demonstrate that, in human kidney, the gene region encompassing the Goodpasture antigen generates at least six alternatively spliced transcripts predicting five distinct proteins that differ in their carboxyl-terminus and retain, except in one case, the exon that harbors the characteristic amino-terminus of the antigen. Goodpasture antibodies specifically recognize recombinant proteins representing the antigen and the alternative form that retains the amino-half of the antigen, suggesting that this moiety could be involved in the in vivo binding of the pathogenic antibodies. Furthermore, the sera of control individuals contain autoantibodies against the antigen that can be differentiated from those causing the syndrome based on their specific reactivities, suggesting that the binding of the pathogenic autoantibodies to a specific determinant likely trigger a distinct and unique cascade of events causing the disease.

Splice-mediated insertion of an Alu sequence in the COL4A3 mRNA causing autosomal recessive Alport syndrome

Alport syndrome is a mainly X-linked hereditary disease of basement membranes characterized by progressive renal failure, deafness, and ocular lesions. The alpha 3(IV) and alpha 4(IV) collagen genes have been recently shown to be involved in the less frequent autosomal recessive form. When screening lymphocyte COL4A3 mRNAs from Alport patients, we found a mutant whose transcripts were disrupted by a 74 bp insertion at the junction of exons IV or V and VI. The insertion derives from an antisense Alu element in COL4A3 intron V, which has been spliced into the alpha 3(IV) mRNA due to a G to T transversion activating a cryptic acceptor splice site in this Alu element. There is complete segregation of this mutation with the disease in the family. Our findings provide the first evidence for the pathogenic role of abnormal splicing of COL4A3. Moreover, we demonstrate the superiority of mutation screening at the mRNA level to detect a hitherto poorly recognized mutation mechanism in humans, splice-mediated insertion of an Alu fragment into a coding sequence.

Production of nitric oxide and peroxynitrite in the lung during acute endotoxemia

Nitric oxide is a short-lived cytotoxic mediator that has been implicated in the pathogenesis of endotoxin-induced tissue injury and septic shock. In the present studies we determined whether this mediator is produced in the lung during acute endotoxemia. We found that intravenous injection of rats with bacterially derived lipopolysaccharide (LPS), a condition that induces acute endotoxemia, caused a time-dependent increase in inducible nitric oxide synthase (iNOS) mRNA expression in the lung, which reached a maximum after 24 h. This was correlated with nitric oxide production in the lung as measured by electron paramagnetic spin trapping, which was detectable within 6 h. Alveolar macrophages (AMs) and interstitial macrophages (IMs) isolated from rats 6-12 h after induction of acute endotoxemia were also found to exhibit increased nitric oxide production in response to in vitro stimulation with interferon-gamma (IFN-gamma) and LPS measured by nitrite accumulation in the culture medium. The effects of acute endotoxemia on nitric oxide production by these cells were, however, transient and returned to control levels by 24 h in AMs and 36 h in IMs. Interestingly, although nitrite accumulation in the culture medium of IMs isolated 48 h after induction of acute endotoxemia and stimulated with low concentrations of IFN-gamma and LPS was reduced, when compared with cells from control animals, these cells, as well as AMs, continued to express high levels of iNOS protein and mRNA. This was correlated with increased peroxynitrite production by the cells. Peroxynitrite has been shown to act as a nitrating agent and can generate nitrotyrosine residues in proteins. Using a specific antibody and immunohistochemistry, we found evidence of nitrotyrosine residues in sections of lungs 48 h after treatment of rats with endotoxin. These data suggest that nitric oxide produced by IMs and AMs can react with superoxide anion to form peroxynitrite. Taken together, the present studies demonstrate that AMs and IMs are activated following acute endotoxemia to produce reactive nitrogen intermediates and that both cell types contribute to inflammatory responses in the lung.

Promoter elements in the transcriptional activation of the human stromelysin-1 gene by the inflammatory cytokine, interleukin 1

Stromelysin-1, a tissue-remodelling metalloproteinase synthesized by fibroblasts, has proteolytic activity against a variety of extracellular matrix components. Stromelysin-1 gene transcription is induced by the inflammatory cytokine interleukin (IL)-1. In fibroblasts transiently transfected with constructs containing 5'-deletion mutants of the human stromelysin-1 gene promoter, IL-1-induced transcriptional activity was abolished with the removal of region -102 to -54. This region includes an AP-1 binding site at positions -70 to -64. The AP-1 site alone increased the basal activity of and conferred minimal IL-1 inducibility onto the heterologous gene promoter of thymidine kinase. Interestingly, although the removal of the AP-1 site from the native promoter (-1303 to +4) affected the absolute levels of IL-1-induced and basal promoter activity, it did not alter their ratio, indicating the involvement of regions outside the AP-1 site in the IL-1 response. Of the stromelysin-1 5' flanking sequence examined, only the region -274 to -54 could confer IL-1 inducibility to a heterologous promoter independently of the AP-1 site. This region also bound specific nuclear factors. Further analysis revealed that the region composed of -86 to -71 and -63 to -54 could independently respond to IL-1 and bind protein of whole cell extracts. Protein binding to this region and to the AP-1 site was modestly induced by IL-1 treatment. From these results we conclude that, in fibroblasts, the AP-1 site (-70 to -64) is not necessary for the IL-1 response; however, it probably interacts through protein associations with the responsive region immediately surrounding it in the absolute transcriptional activation of the human stromelysin-1 gene by IL-1.

The human mRNA encoding the Goodpasture antigen is alternatively spliced

The noncollagenous (NC1) domain of the human collagen alpha 3(IV)-chain is the primary target of autoantibodies produced in Goodpasture syndrome and, therefore, has been designated as the Goodpasture antigen. In this report, we show that Goodpasture antigen mRNA undergoes processing to at least two alternatively spliced forms in a variety of human tissues, resulting in the exclusion of sequence encoded by either one or two exons. Interestingly, no alternatively spliced forms were observed in bovine or rat tissues. The derived amino acid sequences of the two variant mRNA forms are identical and significantly shorter than that arising from the complete Goodpasture antigen mRNA. They lack the carboxyl-terminal region contributing to the formation of the Goodpasture epitope and all but one of the cysteines found in the complete form. These sequence characteristics suggest that, if translated, the variant Goodpasture antigen is likely to be defective in triple helix formation and no longer reactive with Goodpasture autoantibodies. Although each tissue expressing Goodpasture antigen displayed a specific mRNA pattern, the complete form was always the most abundant and was present at levels apparently unrelated to whether or not the organ of origin is a potential target in Goodpasture syndrome. Furthermore, the antigen sequence was identical in the kidneys of normal and Goodpasture-affected individuals, and no major differences in the expression of the complete and spliced forms were observed.

Exon/intron structure of the human alpha 3(IV) gene encompassing the Goodpasture antigen (alpha 3(IV)NC1). Identification of a potentially antigenic region at the triple helix/NC1 domain junction

The Goodpasture antigen has been identified as the non-collagenous (NC1) domain of alpha 3(IV), a novel collagen IV chain (Saus, J., Wieslander, J., Langeveld, J., Quinones, S., and Hudson, B.G. (1988) J. Biol. Chem. 263, 13374-13380). In the present study, the exon/intron structure and sequence for 285 amino acids of human alpha 3(IV), comprising 53 amino acids of the triple-helical domain and the complete NC1 domain (232 amino acids), were determined. Based on the comparison of the amino acid sequences of the alpha 1(IV), alpha 2(IV), alpha 3(IV), and alpha 5(IV) NC1 domains, a phylogenetic tree was constructed which indicates that alpha 2(IV) was the first chain to evolve, followed by alpha 3(IV), and then by alpha 1(IV) and alpha 5(IV). The exon/intron structure of these domains is consistent with this evolution model. In addition, it appears that alpha 3(IV) changed most after diverging from the parental gene. Analysis of its primary structure reveals that, at the junction between the triple-helical and NC1 domains, there exists a previously unrecognized, highly hydrophilic region (GLKGKRGDSGSPATWTTR) which is unique to the human alpha 3(IV) chain, containing a cell adhesion motif (RGD) as an integral part of a sequence (KRGDSGSP) conforming to a number of protein kinase recognition sites. Based on primary structure data, we outline new aspects to be explored concerning the molecular basis of collagen IV function and Goodpasture syndrome.

The AP-1 site is required for basal expression but is not necessary for TPA-response of the human stromelysin gene

We have studied the activity of the AP-1 site, a target for the Fos and Jun family of transcription factors, in the context of the human stromelysin promoter (-1303 to +4). In transiently transfected human HepG2, HeLa and fibroblast cell cultures, point-mutations in any position of the stromelysin AP-1 sequence TGAGTCA (-70 to -64) reduced both the basal level and TPA-induced expression from the stromelysin promoter. TPA-induction fold of the mutant promoters, however, was comparable to that of the wild-type promoter. Similarly, antisense c-Fos mRNA expression reduced basal activity but had no significant effect on the relative TPA-response of the stromelysin promoter. Further, in mouse F9 cells cotransfected with c-Fos and c-Jun expression plasmids, the transfected wild-type stromelysin promoter activity was increased 57-fold whereas no transactivation was detected for an AP-1 mutant stromelysin promoter. In gelshift assays, stromelysin promoter fragments (-101 to -11), containing the mutated AP-1 site, all failed to bind or compete for the in vitro synthesized Fos and Jun proteins. We interpret these data to suggest that the Fos and Jun proteins, or similar activity, and the AP-1 site are required for the basal level expression of the human stromelysin gene. Strikingly, these data also suggest that the stromelysin AP-1 site is not necessary for the TPA-response.

Cycloheximide induces stromelysin mRNA in cultured human fibroblasts

Stromelysin is a metalloproteinase that degrades extracellular matrix macromolecules including fibronectin, laminin, collagen IV and proteoglycans. We now report that cycloheximide, an inhibitor of protein synthesis, induces human stromelysin mRNA in fibroblast cultures in a time- and dose-dependent fashion. As determined by Northern hybridization, a 24-h treatment with cycloheximide increased stromelysin mRNA about 20-fold over the control level. In vitro translation or translation in cells after removal of cycloheximide resulted in increased levels of immunoprecipitable stromelysin suggesting that the cycloheximide-induced stromelysin mRNA was functional. Analysis of mRNA stability suggested that the cycloheximide effect is in part due to the increased activation of the stromelysin gene. In contrast to these results, cycloheximide did not induce collagenase mRNA but, rather, prevented its induction by interleukin-1 beta. These data provide evidence for discoordinate regulation of collagenase and stromelysin genes and suggest that a short-lived repressor protein may play a role in the stromelysin gene expression.

Transcriptional regulation of human stromelysin

We have determined that human stromelysin mRNA can be induced by interleukin-1 beta (IL-1 beta) and that the induced mRNA levels can be suppressed by retinoic acid and dexamethasone (Saus, J., Quinones, S., Otani, Y., Nagase, H., Harris, E.D., Jr., and Kurkinen, M. (1988) J. Biol. Chem. 263, 6742-6745). Here we show, by nuclear run-on and transient gene expression analyses, that IL-1 beta induction is a promoter function and that dexamethasone suppresses IL-1 beta-induced gene activity. For transient gene expression assays, 1.3 kilobase pairs of the stromelysin promoter region (-1303 to -11 relative to the transcription start site) and shorter fragments thereof were cloned into a human growth hormone reporter vector. In transfected human fibroblast cultures all the constructs, with the exception of the one containing the shortest promoter fragment (-53 to -11), responded to IL-1 beta induction. Interestingly, the ability of IL-1 beta to induce human growth hormone expression decreased as the length of the promoter fragment was reduced. Dexamethasone treatment suppressed the induced human growth hormone levels by approximately 50% irrespective of the promoter length. These results suggest that the 1.3-kilobase pairs stromelysin promoter fragment contains DNA elements required for IL-1 beta induction and dexamethasone suppression.

The complete primary structure of mouse alpha 2(IV) collagen. Alignment with mouse alpha 1(IV) collagen

We have determined the nucleotide and amino acid sequences of mouse alpha 2(IV) collagen which is 1707 amino acids long. The primary structure includes a putative 28-residue signal peptide and contains three distinct domains: 1) the 7 S domain (residues 29-171), which contains 5 cysteine and 8 lysine residues, is involved in the cross-linking and assembly of four collagen IV molecules; 2) the triple-helical domain (residues 172-1480), which has 24 sequence interruptions in the Gly-X-Y repeat up to 24 residues in length; and 3) the NC1 domain (residues 1481-1707), which is involved in the end-to-end assembly of collagen IV and is the most highly conserved domain of the protein. Alignment of the primary structure of the alpha 2(IV) chain with that of the alpha 1(IV) chain reported in the accompanying paper (Muthukumaran, G., Blumberg, B., and Kurkinen, M. (1989) J. Biol. Chem. 264, 6310-6317) suggests that a heterotrimeric collagen IV molecule contains 26 imperfections in the triple-helical domain. The proposed alignment is consistent with the physical data on the length and flexibility of collagen IV.

Identification of the Goodpasture antigen as the alpha 3(IV) chain of collagen IV

The organizational relationship between the recently identified alpha 3 chain of basement membrane collagen (Butkowski, R.J., Langeveld, J.P.M., Wieslander, J., Hamilton, J., and Hudson, B.G. (1987) J. Biol. Chem. 262, 7874-7877) and collagen IV was determined. This was accomplished by the identification of subunits in hexamers of the NC1 domain of collagen IV that were immunoprecipitated with antibodies prepared against subunits M1, corresponding to alpha 1(IV)NC1 and alpha 2(IV)NC1, and M2, corresponding to alpha 3NC1, and by amino acid sequence analysis. The presence of at least two distinct types of hexamers was revealed, one enriched in M1 and the other enriched in M2, but in both types, M1 and M2 coexist. Evidence was also obtained for the existence of heterodimers comprised of M1 and M2. These results indicate that M2 is an integral component of the NC1 hexamer of collagen IV. The amino acid sequence of the NH2-terminal region of M2 was found to be highly related to the collagenous-NC1 junctional region of the alpha 1 chain of collagen IV. Therefore, M2 is designated alpha 3(IV)NC1 and its parent chain alpha 3(IV). These findings lead to a new concept about the structure of collagen IV: namely, 1) collagen IV is comprised of a third chain (alpha 3) together with the two classical ones (alpha 1 and alpha 2); the alpha 3(IV) chain exists within the same triple-helical molecule together with the alpha 1(IV) and alpha 2(IV) chains and/or within a separate triple-helical molecule, exclusive of alpha 1(IV) and alpha 2(IV) chains, but connected through the NC1 domains to the classical triple-helical molecule comprised of alpha 1(IV) and alpha 2(IV) chains. Additionally, a portion of those triple-helical molecules exclusive of alpha 1(IV) and alpha 2(IV) chains may be connected to each other through their NC1 domains; and 3) the epitope to which the major reactivity of autoantibodies are targeted in glomerular basement membrane in patients with Goodpasture syndrome is localized to the NC1 domain of the alpha 3(IV) chain.

The complete primary structure of human matrix metalloproteinase-3. Identity with stromelysin

We have determined the complete primary structure for human matrix metalloproteinase-3 (MMP-3), which has 477 residues including a 17-residue signal peptide. The result indicates that MMP-3 is identical with stromelysin (Whitham, S. E., Murphy, G., Angel, P., Rahmsdorf, H.-J., Smith, B. J., Lyons, A., Harris, T. J. R., Reynolds, J. J., Herrlich, P., and Docherty, A. J. P. (1986) Biochem. J. 240, 913-916). A striking result is that MMP-3 and collagenase are 54% identical in sequence, suggesting a common origin for the evolution of the two proteinases. We also show that in human synovial fibroblast cultures human recombinant interleukin-1 beta rapidly induces high levels of MMP-3 mRNA and, conversely, that retinoic acid or dexamethasone can suppress the MMP-3 mRNA levels. Similar results were obtained for human synovial collagenase mRNA. The data suggest that MMP-3 and collagenase expression are coordinately modulated in synovial fibroblast cultures.

Extensive homology between the carboxyl-terminal peptides of mouse alpha 1(IV) and alpha 2(IV) collagen

We have determined the complete primary structure for the carboxyl-terminal peptides of mouse alpha 1(IV) and alpha 2(IV) collagen; which have 229 and 227 amino acids, respectively. The amino acid sequences are 63% identical and conservatively substituted in 28 positions. A striking feature of these peptides is that the first half of each sequence is homologous with the second half, 37% in alpha 1(IV) and 36% in alpha 2(IV). These results suggest that the carboxyl-terminal peptides of type IV collagen are closely related in their structure and evolution. Presumably, they were first derived by internal duplication of a common ancestral DNA sequence which later, by gene duplication, gave rise to the two different but homologous carboxyl-terminal peptides of type IV collagen.