Biomedical subjects

Elizabeth Hayes

Publications and source records attributed to Elizabeth Hayes.

5 recordsLinked to original sources

PubMed2005

Differentiation-induced loss of heparan sulfate in human exostosis derived chondrocytes.

An exostosis or osteochondroma is an aberrant bony growth occurring next to the growth plate either as an isolated growth abnormality or as part of the Hereditary Multiple Exostosis (HME) syndrome. Mutations in either exostosin 1 (EXT1) or exostosin 2 (EXT2) gene cause the HME syndrome and also some isolated osteochondromas. The EXT1 and EXT2 genes are glycosyltransferases that function as hetero-oligomers in the Golgi to add repeating glycosaminoglycans (GAGs) to heparan sulfate (HS) chains. Previously, we demonstrated that HS is markedly diminished in the exostosis cartilage cap and that the HS proteoglycan, perlecan, has an abnormal distribution in these caps. The present studies were undertaken to evaluate which chondrocyte-specific functions are associated with diminished HS synthesis in human chondrocytes harboring either EXT1 or EXT2 mutations. Systematic evaluation of exostosis cartilage caps and chondrocytes, both in vitro and in vivo, suggests that chondrocyte-specific cell functions account for diminished HS levels. In addition, we provide evidence that perichondrial cells give rise to chondrocytes that clonally expand and develop into an exostosis. Undifferentiated EXT chondrocytes synthesized amounts of HS similar to control chondrocytes; however, EXT chondrocytes displayed very poor survival in vitro under conditions that promote normal chondrocyte differentiation with high efficiency. Collectively, these observations suggest that loss of one copy of either the EXT1 or EXT2 gene product compromises the perichondrial chondrocytes' ability to differentiate normally and to survive in a differentiated state in vitro. In vivo, these compromised responses may lead to abnormal chondrocyte growth, perhaps from a perichondrial stem cell reserve.

Cell Differentiation↗

PubMed2004

COMP mutations, chondrocyte function and cartilage matrix.

Cartilage oligomeric matrix protein (COMP) is a large extracellular pentameric glycoprotein found in the territorial matrix surrounding chondrocytes. More than 60 unique COMP mutations have been identified as causing two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1). Recent studies demonstrate that calcium-binding and calcium induced protein folding differ between wild type and mutant COMP proteins and abnormal processing of the mutant COMP protein causes the characteristic large lamellar appearing rough endoplasimic reticulum (rER) cisternae phenotype observed in PSACH and EDMI growth plate chondrocytes. To understand the cellular events leading to this intracellular phenotype, PSACH chondrocytes with a G427E, D469del and D511Y mutations were grown in 3-D culture to produce cartilage nodules. Each nodule was assessed for the appearance and accumulation of cartilage-specific proteins within the rER and for matrix protein synthesis. All three COMP mutations were associated with accumulation of COMP in the rER cisternae by 4 weeks in culture, and by 8 weeks the majority of chondrocytes had the characteristic cellular phenotype. Mutations in COMP also affect the secretion of type IX collagen and matrilin-3 (MATN3) but not the secretion of aggrecan and type II collagen. COMP, type IX collagen and MATN3 were dramatically reduced in the PSACH matrices, and the distribution of these proteins in the matrix was diffuse. Ultrastructural analysis shows that the type II collagen present in the PSACH matrix does not form organized fibril bundles and, overall, the matrix is disorganized. The combined absence of COMP, type IX collagen and MATN3 causes dramatic changes in the matrix and suggests that these proteins play important roles in matrix assembly.

Calcium↗

PubMed2004

Role of TSP-5/COMP in pseudoachondroplasia.

Pseudoachondroplasia (PSACH) is a well-characterized dwarfing condition associated with disproportionate short stature, abnormal joints and osteoarthritis requiring joint replacement. PSACH is caused by mutations in cartilage oligomeric matrix protein (COMP). COMP, the fifth member of the thrombospondin (TSP) gene family, is a pentameric protein found primarily in the extracellular matrix of musculoskeletal tissues. Functional studies have shown that COMP binds types II and IX collagens but the role of COMP in the extracellular matrix remains to be defined. Mutations in COMP interfere with calcium-binding and protein conformation. PSACH growth plate and growth plate chondrocytes studies indicate that COMP mutations have a dominant negative effect with both COMP and type IX collagen being retained in large rER cisternae. This massive retention causes impaired chondrocyte function with little COMP secreted into the matrix and premature loss of chondrocytes. Deficiency of linear growth results from loss of chondrocytes from the growth plate. Secondarily, the matrix contains minimal COMP, which may be normal and/or mutant, and little type IX collagen. This deficiency results in abnormal joints that are easily eroded and cause painful osteoarthritis. Unlike other misfolded proteins that are targeted for degradation, much of the retained COMP escapes degradation, compromises cell function, and causes cell death. Gene therapy will need to target the reduction of COMP in order to restore normal chondrocyte function and longevity.

Achondroplasia↗

PubMed2004

Chondrocyte cell death and intracellular distribution of COMP and type IX collagen in the pseudoachondroplasia growth plate.

Cartilage oligomeric matrix protein (COMP) is a large extracellular matrix protein expressed in cartilage, ligament and tendon. Mutations in the COMP gene cause two dominantly inherited skeletal dysplasias, pseudoachondroplasia (PSACH) and Multiple Epiphyseal Dysplasia (MED/EDM1). We report on a novel point mutation D511Y in the seventh calcium-binding repeat of the COMP gene and the resulting iliac crest growth plate pathology. The PSACH iliac crest growth plate is comprised of a large region of resting chondrocytes above a narrow region composed of clusters of disorganized proliferative and hypertrophic chondrocytes. Chondrocytes in all zones show massive intracellular retention of COMP and the surrounding extracellular matrix is deficient in COMP. Moreover, the 511Y COMP mutation selectively affects type IX collagen as little is found in the growth plate matrix whereas type II collagen and aggrecan are abundant in the matrix. Chondrocyte remnants are observed in the chondrocyte clusters and dead cells are found throughout the growth plate. Apoptosis studies demonstrate an unusual pattern of TUNEL staining in the PSACH chondrocytes compared to the control growth plate. These in vivo findings support our previous observation that retention of COMP leads to chondrocyte death. These results also add to the increasing evidence that PSACH and EDM1 are rER storage diseases and that impaired linear growth and joint erosion are caused by the disruptive effect of massive amounts of COMP within the chondrocytes.

Achondroplasia↗

PubMed2003

Advantage of rare HLA supertype in HIV disease progression.

The highly polymorphic human leukocyte antigen (HLA) class I molecules help to determine the specificity and repertoire of the immune response. The great diversity of these antigen-binding molecules confers differential advantages in responding to pathogens, but presents a major obstacle to distinguishing HLA allele-specific effects. HLA class I supertypes provide a functional classification for the many different HLA alleles that overlap in their peptide-binding specificities. We analyzed the association of these discrete HLA supertypes with HIV disease progression rates in a population of HIV-infected men. We found that HLA supertypes alone and in combination conferred a strong differential advantage in responding to HIV infection, independent of the contribution of single HLA alleles that associate with progression of the disease. The correlation of the frequency of the HLA supertypes with viral load suggests that HIV adapts to the most frequent alleles in the population, providing a selective advantage for those individuals who express rare alleles.

Amino Acid Motifs↗