EFFECT OF MECHANICAL STRESS (STRETCH) ON THE CONTENT OF GLYCOSAMINOGLYCANS-GAGs

[Abbas Bubakar El-ta'alu]

EFFECT OF MECHANICAL STRESS (STRETCH) ON THE CONTENT OF GLYCOSAMINOGLYCANS (GAGs) IN RAT'S SKIN.

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KOT, Y. G* and EL-TA'ALU, A. B**

*Department of Biochemistry; ** Department of Human Physiology,
V. N. Kharkov National University,
Kharkov 61077, Svobody Square № 4, Ukraine.

A paper presented, in Ukrainian language, in the II International Comference, "Biology: from Molecules to Biosphere", 19th – 21st November, 2007, in V. N. Kharkov Kharkov National University, Ukraine.
                                             
          Playing the role of structural and functional components of the extracellular matrix (ECM), glycosaminoglycans (GAGs) must participate in the response of connective tissue structures to the action of such an external environmental factor as mechanical stress. At the moment, there is no data on relative reaction of its carbohydrate matrix components.
          Changes due to the effect of mechanical stress, on total and collagen-bound glycosaminoglycan (Hyaluronic acid, Chondroitin-, Keratan-, Dermatan- and Heparan sulphates) concentrations, as well as their contents in sub-molecular collagen formations, were in vitro studied.
Investigations were carried out using male rat's skin, samples of which were incubated and stretched under the effect of mechanical stretching or loading. While in determining total GAG concentration, samples of skin were hydrolysed with papain and collagenase, type I collagen was extracted from the skin samples to determine the concentration of GAG-bound collagen, which appeared in a complex with cytylpyridinium chloride. The obtained type I collagen was hydrolysed using enzymes. Fractionalisation of GAG was carried out by ion-exchange chromatography on Dowex 1 x 2.
          Obtained results provided evidences, that dependence of total GAG concentration on magnitude of mechanical stress represents a curve, with maximum stress, where an increase in Hyaluronic acid and all investigated sulphated GAGs, with the exception of Keratan sulphate, was observed. With subsequent increase in magnitude of mechanical stress, the character of changes in concentrations of different GAG fractions were considerably different: maximum Hyaluronic acid concentration was found to be merged in regions of higher magnitude of mechanical stress, where minimal concentrations of Dermatan- and Chondroitin sulphates, and increased concentration of Keratan sulphate were observed. A sharp decrease in Hyaluronic acid and collagen-bound sulphated GAGs was observed due to the action of mechanical stress. An exception was found with Heparan sulphate, the concentration of which, in collagen-bound fractions increased.
          Therefore, under the effect of mechanical stress, quantitative and qualitative changes in concentrations of sulphated GAGs are observed. The obtained results permit the admission, that sub-molecular matrix collagen formations, produced in the skin under the effect of mechanical stress, are unmatured. Observed increases in Hyaluronic acid concentration, against the sharp decrease in Dermatan- and Chondroitin sulphate concentrations may be a compensatory mechanism in which Hyaluronic acid plays a protective function, by averting excess enzymatic degradation of collagenous fibrils. It is possible, that different systems of synthesis of different connective tissue matrix GAGs respond differently (with different intensity) to the effect of mechanical stress. The mechanism of this phenomenon is a subject of discussion.


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