The hallmark of fibrotic processes is an excessive accumulation of collagen. The deposited collagen shows an increase in pyridinoline cross-links, which are derived from hydroxylated lysine residues within the telopeptides. This change in cross-linking is related to irreversible accumulation of collagen in fibrotic tissues. The increase in pyridinoline cross-links is likely to be the result of increased activity of the enzyme responsible for the hydroxylation of the telopeptides (telopeptide lysyl hydroxylase, or TLH). Although the existence of TLH has been postulated, the gene encoding TLH has not been identified. By analyzing the genetic defect of Bruck syndrome, which is characterized by a pyridinoline deficiency in bone collagen, we found two missense mutations in exon 17 of PLOD2, thereby identifying PLOD2 as a putative TLH gene. Subsequently, we investigated fibroblasts derived from fibrotic skin of systemic sclerosis (SSc) patients and found that PLOD2 mRNA is highly increased indeed. Furthermore, increased pyridinoline cross-link levels were found in the matrix deposited by SSc fibroblasts, demonstrating a clear link between mRNA levels of the putative TLH gene (PLOD2) and the hydroxylation of lysine residues within the telopeptides. These data underscore the significance of PLOD2 in fibrotic processes.The biosynthesis of collagen molecules involves several intracellular post-translational modifications followed by excretion and extracellular aggregation of the collagen molecules into fibrils, which are subsequently stabilized by intermolecular cross-links (1, 2). Two related routes are responsible for the formation of these collagen cross-links, namely the allysine route, in which a lysine residue in the telopeptide is converted by lysyl oxidase into the aldehyde allysine, and the hydroxyallysine route, in which a hydroxylysine residue in the telopeptide is converted into the aldehyde hydroxyallysine. Subsequently, the allysine or the hydroxyallysine reacts with a Lys or Hyl residue in the triple helix to form di-, tri-, or tetrafunctional cross-links (3-6). The mature cross-links hydroxylysylpyridinoline or lysylpyridinoline are formed via the hydroxyallysine route and occur in a variety of connective tissues such as bone, tendon, ligaments, and cartilage (7). In contrast, collagen in the skin is mainly cross-linked via the allysine route. Interestingly, in fibrotic skin (lipodermatosclerosis, keloid) and organ fibrosis (lung, liver), which is characterized by an excessive accumulation of collagen, an increase in crosslinks derived from the hydroxyallysine route is found (8 -15). It has been shown that the amount of hydroxyallysine-derived cross-links is related to the irreversible accumulation of collagen in fibrotic tissues, indicating that collagen containing hydroxyallysine-derived cross-links is more difficult to degrade than collagen containing allysine-derived cross-links (10 -12, 14, 15). Inhibition of the formation of hydroxyallysine-derived cross-links in fibrosis is therefore likely to resu...

Bruck syndrome is characterized by the presence of osteoporosis, joint contractures, fragile bones, and short stature. We report that lysine residues within the telopeptides of collagen type I in bone are underhydroxylated, leading to aberrant crosslinking, but that the lysine residues in the triple helix are normally modified. In contrast to bone, cartilage and ligament show unaltered telopeptide hydroxylation as evidenced by normal patterns of crosslinking. The results provide compelling evidence that collagen crosslinking is regulated primarily by tissue-specific enzymes that hydroxylate only telopeptide lysine residues and not those destined for the helical portion of the molecule. This new family of enzymes appears to provide the primary regulation for controlling the different pathways of collagen crosslinking and explains why crosslink patterns are tissue specific and not related to a genetic collagen type. A genome screen identified only a single region on chromosome 17p12 where all affected sibs shared a cluster of haplotypes identical by descent; this might be the BS (Bruck syndrome) locus and consequently the region where bone telopeptidyl lysyl hydroxylase is located. Further knowledge of this enzyme has important implications for conditions where aberrant expression of telopeptide lysyl hydroxylase occurs, such as fibrosis and scar formation.Collagen fibrils are important for the mechanical strength of bone (1-2). The tensile properties of fibrils result from intermolecular crosslinks connecting the nonhelical ends of a collagen molecule (telopeptides) with the triple helical part of an adjacent molecule (2-3). More than ten different collagen crosslinks are known; their structure, number, and location are highly tissue specific and not related to a specific collagen type (4-8). Stereochemical and x-ray diffraction studies revealed that differences in molecular packing of collagen within fibrils are associated with differences in crosslink profiles (9-12). Proper mineralization probably depends on a correct alignment of collagen molecules, as nucleation of calcium apatite crystals starts in the gap region, i.e., in the area adjacent to the crosslink site (9). Alterations in crosslink patterns associated with changes in the molecular packing are, therefore, expected to result in aberrant mineralization.Residues involved in crosslinking are mainly the amino acids lysine (Lys) or hydroxylysine (Hyl) (4-8). The enzyme lysyl hydroxylase (LH) (procollagen-lysine, 2-oxoglutarate 5-dioxygenase; EC 1.14.11.4) catalyzes the conversion of Lys into Hyl (13-15). Crosslinking is initiated only after specific Lys or Hyl residues of the telopeptides are converted extracellularly by the enzyme lysyl oxidase into the aldehydes allysine and hydroxyallysine, respectively (4-8). The aldehydes subsequently react with Lys, Hyl, or histidyl, residues of the triple helix to give characteristic di-, tri-, and tetrafunctional crosslinks. Two related routes for the formation of crosslinks have been described, based on ...

Paragangliomas of the head and neck are slow growing tumors which rarely show malignant progression. Familial transmission has been described consistent with an autosomal dominant mode of inheritance. Clinical manifestations of hereditary paragangliomas are determined by the sex of the transmitting parent. All affected individuals have inherited the disease gene from their father, expression of the phenotype is not observed in the offspring of an affected female until subsequent transmittance of the gene through a male carrier. This finding strongly suggests that genomic imprinting is involved. We report the results of a linkage study on a large Dutch pedigree with hereditary paragangliomas. Highly significant evidence for genetic linkage to chromosome 11q23-qter with the anonymous DNA marker D11S147 was detected with a peak lod score of 6.0 at a recombination fraction theta = 0.0. Likelihood calculations yielded an odds ratio of 2.7 x 10(6) in favor of genomic imprinting versus the absence of genomic imprinting.

Several lines of evidence, including expression analyses, brain imaging and genetic studies suggest that the integrity of myelin is disturbed in schizophrenia patients. In this study, we first reconstructed a pathway of 138 myelin-related genes, all involved in myelin structure, composition, development or maintenance. Then we performed a two-stage association analysis on these 138 genes using 771 single nucleotide polymorphisms (SNPs). Analysis of our data from 310 cases vs 880 controls demonstrated association of 10 SNPs from six genes. Specifically, we observed highly significant P-values for association in PIK4CA (observed P = 6.1 Â 10 À6 ). These findings remained significant after Bonferroni correction for 771 tests. The PIK4CA gene is located in the chromosome 22q11 deletion syndrome region, which is of particular interest because it has been implicated in schizophrenia. We also report weak association of SNPs in PIK3C2G, FGF1, FGFR1, ARHGEF10 and PSAP (observed Pp0.01). Our approach-of screening genes involved in a particular pathway for association-resulted in identification of several, mostly novel, genes associated with the risk of developing schizophrenia in the Dutch population.

Chondrosarcomas are malignant cartilaginous tumors arising centrally in bone (central chondrosarcoma), or secondarily within the cartilaginous cap of osteochondroma (peripheral chondrosarcoma). We previously used DNA flow cytometry to demonstrate that near-haploidy is relatively frequent in peripheral chondrosarcomas. We performed fluorescence in situ hybridization (FISH) to interphase nuclei using centromeric probes, a genome wide loss of heterozygosity (LOH) analysis, and comparative genomic hybridization on five peripheral chondrosarcomas. We demonstrated near-haploidy in two low-grade tumors with only one copy and LOH of most chromosomes. Few chromosomes are disomic, with retention of heterozygosity and overrepresentation at comparative genomic hybridization. One tumor contains both a near-haploid clone with chromosomes in monosomic and disomic state, and an exactly duplicated clone. Two high-grade tumors clearly demonstrate polyploidization because most chromosomes show LOH and two copies at FISH, whereas few chromosomes have four copies with retention of heterozygosity. Using DNA from a relative, we demonstrate that chromosome loss is random regardless of parental origin. Using FISH on paraffin slides, we exclude near-haploidy to result from meiosis-like division in binucleated cells, characteristic for chondrosarcoma. In conclusion, our results indicate that near-haploidy characterizes the progression from osteochondroma toward low-grade chondrosarcoma. Moreover, further progression toward high-grade chondrosarcoma is characterized by polyploidization. Chondrosarcoma, the second most common primary malignant bone tumor after osteosarcoma, is a malignant cartilage-forming tumor occurring predominantly in adults. The majority of chondrosarcomas develops de novo and is located centrally within the medullary cavity (central chondrosarcoma). In contrast, ϳ15% arise within the cartilage cap of a long-standing osteochondroma (peripheral chondrosarcoma), mostly in patients suffering from the hereditary multiple exostoses syndrome. Hereditary multiple exostoses syndrome is a familial disorder with an autosomal dominant mode of inheritance.1-4 Malignant transformation is estimated to occur in 1 to 5% of osteochondromas.The development of peripheral chondrosarcoma results in genetic instability characterized by a high percentage of loss of heterozygosity (LOH) and a wide variation in DNA ploidy.5 LOH in peripheral chondrosarcoma most frequently involves the TP53 (80%), RB1 (71%), and EXT1 (65%) loci. 5 In contrast, peridiploidy and a low percentage of LOH in central tumors indicates that a different oncogenic molecular mechanism may be operative. 5 We have detected hypodiploidy, which is uncommon for human solid tumors, in 29% of peripheral chondrosarcomas and not in central chondrosarcomas.5 Others mention hypodiploidy in 8 to 31% of chondrosarcomas without further subclassification.6 -9 Near-haploidy, which is a very rare phenomenon in human solid tumors in general, is found especially in low-grade peripheral chon...