Histochemical Localization of Uridine Diphosphoglucose Dehydrogenase in Cartilage

UDP-glucose dehydrogenase (UGDH) activity is suppressed by peroxide and promoted by PDGF in fibroblast-like synoviocytes: Evidence of a redox control mechanism

UDP-glucose dehydrogenase (UGDH) generates essential precursors of hyaluronic acid (HA) synthesis, however mechanisms regulating its activity are unclear. We used enzyme histostaining and quantitative image analysis to test whether cytokines that stimulate HA synthesis upregulate UGDH activity. Fibroblast-like synoviocytes (FLS, from N = 6 human donors with knee pain) were cultured, freeze-thawed, and incubated for 1 hour with UDP-glucose, NAD+ and nitroblue tetrazolium (NBT) which allows UGDH to generate NADH, and NADH to reduce NBT to a blue stain. Compared to serum-free medium, FLS treated with PDGF showed 3-fold higher UGDH activity and 6-fold higher HA release, but IL-1beta/TGF-beta1 induced 27-fold higher HA release without enhancing UGDH activity. In selected proliferating cells, UGDH activity was lost in the cytosol, but preserved in the nucleus. Cell-free assays led us to discover that diaphorase, a cytosolic enzyme, or glutathione reductase, a nuclear enzyme, was necessary and sufficient for NADH to reduce NBT to a blue formazan dye in a 1-hour timeframe. Primary synovial fibroblasts and transformed A549 fibroblasts showed constitutive diaphorase/GR staining activity that varied according to supplied NADH levels, with relatively stronger UGDH and diaphorase activity in A549 cells. Unilateral knee injury in New Zealand White rabbits (N = 3) stimulated a coordinated increase in synovial membrane UGDH and diaphorase activity, but higher synovial fluid HA in only 2 out of 3 injured joints. UGDH activity (but not diaphorase) was abolished by N-ethyl maleimide, and inhibited by peroxide or UDP-xylose. Our results do not support the hypothesis that UGDH is a rate-liming enzyme for HA synthesis under catabolic inflammatory conditions that can oxidize and inactivate the UGDH active site cysteine. Our novel data suggest a model where UGDH activity is controlled by a redox switch, where intracellular peroxide inactivates, and high glutathione and diaphorase promote UGDH activity by maintaining the active site cysteine in a reduced state, and by recycling NAD+ from NADH.

A quantitative cytochemical study of UDP-D-glucose: NAD-oxidoreductase (E.C. 1.1.1.22) activity during stelar differentiation in Pisum sativum L. cv Meteor

A quantitative cytochemical assay for UDP-D-glucose dehydrogenase (UDPGD) activity employing scanning and integrating microdensitometry has been revised and applied to a study of this enzyme during the initiation of secondary cell wall biosynthesis during the formation of primary vascular tissues in roots of Pisum sativum L. cv Meteor. The reaction involves the use of NBT as final electron acceptor and is inhibited 10-fold by either 10 mM UDP-D-xylose or 25 mM UDP-D-glucuronic acid, two molecules involved in feed-back inhibition of UDPGD activity in vivo. UDPGD is a far-from equilibrium enzyme representing a flux-generating step in the biosynthesis of precursors for hemicelluloses involved in secondary cell wall construction, and can be demonstrated to increase sharply in activity in cells of the developing primary vascular elements. This changed activity occurs 18-20 cells back from the root cap junction and coincides with the first cells containing the activated programme for secondary cell wall synthesis.

Osteogenesis imperfecta: morphological, histochemical and biochemical aspects. Modifications induced by (+)-catechin

Two patients affected with two different forms of Osteogenesis Imperfecta were examined in order to study collagen and glycosaminoglycans (GAGs) in skin and iliac crest cartilage. A sharp decrease of the galactosamine to glucosamine ratio due to a reduced content of chondroitin sulfate was evidenced in both patients. Moreover the structure of proteoglycans appeared altered, this being more evident in the severe form of the disease. Morphological examination in light and electron microscopy of cartilage of the less severely diseased patient showed that GAGs in the extracellular matrix did not present regular connection with collagen fibers. Chondrocytes, elongated and disorderly scattered, showed large lipidic inclusions and, on histochemical basis, were devoid of UDPG dehydrogenase activity. Treatment with (+)-catechin produced an improvement, in both patients, of the biochemical pattern of collagen and GAGs. Similarly a shift of the cellular activity and of the matrix morphology towards normality was observed in the investigated cartilage of the less severely affected patient.

[Aortic development and ageing in the rat aorta -- Comparative histochemical and histoenzymological study (author's transl)]

A comparative study was made of 36 aortic enzyme activities (E.A.) and 6 macromelecular substances at different stages of ontogenesis in 49 male rats. In the foetal aorta (19th day) the E.Z. were moderate or weak and restricted to a few metabolic pathways: glycolysis, diaphorases, esterolysis of some nucleotides and glucosaminoglycan (GAG) metabolism. During the neonatal period (1st-3rd day), the pre-existing E.A. increased; some aerobic and lipolytic activities became histochemically detectable; longitudinal and radial gradients became established. These changes seemed to provide evidence of increased morphogenic activities and metabolic exchanges. During the prepuberty and puberty period (10-20th day-2nd month) all the E.A., as well as metachromasis and pyroniophilia increased, and new E.A. appeared (GluDH, GPDH, 5/Nase, Ac.Pase-Ca++, Mg++, pH 7.2). These changes appeared to be related to cell proliferation and connective tissue increase during the period of fast aortic growth. The increase of some E.A. (Est/ase, Ch. est, ATPase-Ca++, Mg++, 5/Nase, Alk. Pase) suggested a correlation between enzymatic differentiation and hormonal maturation. During adulthood (6-12th month), the E.A. were stable except for 5/Nase, lysosomal and lipolytic activities which increased. Some E.A. were found to be high (diaphorases, glycolytic and esterolytic enzymes), or moderate (aerobic oxidoreductases, lysosome, lipolysis and GAG-linked E.A.), while others were weak or absent (glycogen pathway E.A.). These observations seemed to correlate with synthetic processes and defence mechanisms. Ageing (17th month) was characterized by an increase of metachromatic GAG and acid lipids and by a decrease of pyroninophillia. Lysosome, glycolysis and phospholipogenesis-linked E.A. increased. In some animals (individual reactivity) kreb's cycle and lypolysis-E.A. decreased.