Glycosaminoglycan therapy prevents TGF-β1 overexpression and pathologic changes in renal tissue of long-term diabetic rats

Chronic induction of the prosclerotic cytokine transforming growth factor β (TGF-β) has been implicated in the pathogenesis of diabetic nephropathy. In a rat model of diabetes mellitus-induced glomerulosclerosis, daily administration of a modified heparin (mH) glycosaminoglycan (GAG) preparation with low anticoagulant activity prevented glomerular and tubular matrix accumulation, as well as overexpression of TGF-β1 mRNA and albuminuria, without obvious side effects. To elucidate the molecular mechanisms of GAG/mH inhibitory actions on TGF-β1, studies using cultured mesangial cells were also performed. In these cells, high glucose-induced, dose-dependent increases in TGF-β1 mRNA and bioactive TGF-β protein expression were inhibited by GAG/mH treatment, whereas basal TGF-β1 expression was not affected. Both the heparin-derived GAG and dermatan sulfate were effective, indicating that the heparin chemical structure is not necessary for inhibitory activity. Coincubation of GAG with active TGF-β1 demonstrated no inhibitory effect on TGF-β1 bioactivity, excluding a neutralizing effect of GAG on TGF-β1 at the protein level. Furthermore, it was demonstrated that GAG inhibited phorbol myristate acetate-induced translocation of protein kinase C-α (PKC-α) and -β1 and activation of PKC-α, as well as high glucose-induced activation of PKC-α. These results suggest that GAG inhibit TGF-β1 overexpression at the transcriptional level, possibly via inhibition of high glucose-activated PKC. The findings indicate the potential of GAG therapy for the prevention of diabetic glomerulosclerosis by the inhibition of chronic disease-induced TGF-β1 mRNA overexpression.