Glycosaminoglycan therapy prevents TGF-beta 1 overexpression and pathologic changes in renal tissue of long-term diabetic rats

Chronic induction of the prosclerotic cytokine transforming growth factor b eta (TGF-beta) has been implicated in the pathogenesis of diabetic nephropa thy. In a rat model of diabetes mellitus-induced glomerulosclerosis, daily administration of a modified heparin (mH) glycosaminoglycan (GAG) preparati on with low anticoagulant activity prevented glomerular and tubular matrix accumulation, as well as overexpression of TGF-Beta1 mRNA and albuminuria, without obvious side effects. To elucidate the molecular mechanisms of GAG/ mH inhibitory actions on TGF-beta1, studies using cultured mesangial cells were also performed. In these cells, high glucose-induced, dose-dependent i ncreases in TGF beta1 mRNA and bioactive TGF-beta protein expression were i nhibited by GAG/mH treatment, whereas basal TGF-beta1 expression was not af fected. Both the heparin-derived GAG and dermatan sulfate were effective, i ndicating that the heparin chemical structure is not necessary for inhibito ry activity. Coincubation of GAG with active TCF-beta1 demonstrated no inhi bitory effect on TGF-beta1 bioactivity, excluding a neutralizing effect of GAG on TGF-beta1 at the protein level. Furthermore, it was demonstrated tha t GAG inhibited phorbol myristate acetate-induced translocation of protein kinase C-alpha (PKC-alpha) and -beta1 and activation of PKC-alpha, as well as high glucose-induced activation of PKC-alpha. These results suggest that GAG inhibit TGF-beta1 overexpression at the transcriptional level, possibl y via inhibition of high glucose activated PKC. The findings indicate the p otential of GAG therapy for the prevention of diabetic glomerulosclerosis b y the inhibition of chronic disease-induced TGF-beta1 mRNA overexpression.