Age-related Changes in Human Bone Proteoglycan Structure: IMPACT OF OSTEOGENESIS IMPERFECTA

Proteoglycans (PGs) are a family of molecules that undergo extensive post-translational modifications that include addition of glycosaminoglycan (GAG) chains as well as N- and O-linked oligosaccharides to the protein core. PG composition and structure have been reported to alter with age. To test whether the post-translational modifications to PGs can serve as in vitro surrogate end point markers for chronological age, the extent of GAG modifications was determined for PGs derived from normal human bone cells of 14 donors (age range, fetal to 60 years). Isolated cells were steady state radiolabeled with (35)SO(4)(2-) and [(3)H]GlcN. For biglycan and decorin, iduronate content was linearly correlated with age (increased 1.5x between fetal and age 60 years). For the syndecan-like heparan sulfate PG, the N-sulfation of post-natal cells increased over 3.5-fold until reaching a plateau during the 4th decade of life. The amount of O-linked oligosaccharides was also found to decrease as a function of increasing normal donor age, whereas the specific activity of the metabolic precursor pool remained constant regardless of donor age. These age-related changes in post-translational modifications were then used to demonstrate that osteoblasts derived from patients with osteogenesis imperfecta did not exhibit facets of a pre-mature aging, but rather were arrested in a fetal-like phenotypic state. A growth matrix rich in thrombospondin altered PG metabolism in osteoblastic cells, resulting in the production and secretion of the fetal-like (rich in O-linked oligosaccharides) forms of decorin and biglycan. This effect was qualitatively different from the effect of transforming growth factor-beta, which predominantly altered GAGs rather than O-linked oligosaccharides. No other Arg-Gly-Asp protein (fibronectin, vitronectin, type I collagen, osteopontin, and bone sialoprotein) showed any detectable effect on PG metabolism in bone cells. These results indicate that a proper matrix stoichiometry is critical for metabolism of PGs

Correlation of Heparan Sulfate Proteoglycan Structure and Metabolism With the Regulation of Cell Division

232 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.Heparan sulfate proteoglycan (HSPG), a ubiquitous cell surface component in animal cells, is a complex, polyanionic macromolecule consisting of a core protein to which are attached several heparan sulfate (HS) chains. Growing and confluent cultures of a rat hepatocyte cell line were labeled with \sp{35}SO\sb4\sp{2-} and the HS in the culture medium, the pericellular matrix, the nucleus, the outer nuclear membrane, and the remaining cytoplasmic pool was purified by DEAE-cellulose chromatography. The HS in all pools from the confluent cells exhibited a higher average charge density than the corresponding pools from the growing cells. Analysis of the mixtures of di- and tetrasaccharides formed by cleavage of HS with nitrous acid showed that the structural features of the HS in each pool were different and were altered significantly when growing cells became confluent. The nuclear HS was structurally unique and possessed a high content of sulfated glucuronic acid (GlcUA). The correlation of the levels and structures of HS with cell growth was also observed in primary rat hepatocytes which do not divide in culture, in two rat hepatoma cell lines which exhibited no density-dependent inhibition of growth, and in cytolytic thymic lymphocytes which require interleukin 2 to proliferate. Primary hepatocytes synthesized HS with a structure similar to that made by confluent cultures of the hepatocyte cell line and the nuclear pools contained an elevated sulfated-GlcUA content. The hepatomas produced low levels of HS and the nuclear pools lacked the high content of sulfated GlcUA residues. The lymphocytes exhibited a consistent difference in HS metabolism in the quiescent versus the proliferative state. The addition of HSPG, prepared from confluent monolayers of a rat hepatocyte cell line, to synchronized cultures released from block at the Gl/S boundary arrested the cells in the following Gl phase. Studies of (\sp{35}SO\sb4) HSPG and \sp{35}SO\sb4\sp{2-} uptake and metabolism by synchronized cultures of the hepatocytes revealed a similar pattern of cell cycle-dependent appearance and disappearance of nuclear HS. These results confirm a correlation of HS metabolism with the regulation of cell division.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Bone marrow microenvironment in myelomagenesis: its potential role in early diagnosis

Multiple myeloma (MM) is the second most common hematological malignancy, with an overall survival of 4–6 years. It is always preceded by a premalignant stage called monoclonal gammopathy of unknown significance (MGUS). Importantly, at this time we lack reliable predictors to determine who will progress from MGUS to MM, and who will remain stable. The bone marrow microenvironment plays a key role in myelomagenesis (growth, survival and migration of malignant plasma cells). In the present review, we summarize and discuss our current understanding of the bone marrow microenvironment and its compartments in relation to myelomagenesis. Although it remains to be proven, we believe that an improved characterization of the cellular constituents, the extracellular matrix components and the soluble factors of the bone marrow could open up novel avenues to better understand underlying mechanisms of the transformation from MGUS to MM. Ultimately, this will lead to the development of early treatment of high-risk precursor disease aimed to delay/prevent MM

Elevated levels of neopterin in sleep-disordered breathing

Sleep-disordered breathing (SDB) is increasingly being recognized as an independent risk factor for hypertension and cardiovascular disease. Recent evidence suggests that the maladaptive physiologic response to SDB, particularly cardiovascular effects, may result in part from systemic inflammation. Although abnormal cytokine levels have been documented in SDB, data on whether SDB is associated with cellular activation are limited. Thus, this investigation sought to determine whether neopterin, a marker released by activated macrophages, is increased in SDB. Fifty-five men, free of medical comorbidity, undergoing polysomnography had fasting serum tested for neopterin levels. Multivariable regression methods were used to quantify the association between neopterin and quartiles of the apnea hypopnea index (AHI) while accounting for body mass index, waist circumference, and percentage of body fat. Quartiles of AHI (I: 36.82 events per hour) indicated a range from no SDB through severe SDB. Compared to the subjects in the first AHI quartile, serum neopterin levels were higher by 3.0%, 10.9%, and 26.5% in the second, third, and fourth AHI quartiles, respectively (p < 0.001for linear trend). Neopterin levels also were higher in those with greater degree of sleep-related hypoxemia, more stage 1 sleep, and less stage 2 sleep. The results of this study indicate that severity of SDB independently associates with serum levels of neopterin, a marker for macrophage activation that may play an important role in the pathogenesis of SDB-related cardiovascular disease