Published in:
01-04-2008 | Article
Increased renal gene transcription of protein kinase C-β in human diabetic nephropathy: relationship to long-term glycaemic control
Published in: Diabetologia | Issue 4/2008
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Aims/hypothesis
Activation of protein kinase C (PKC) isoforms has been implicated as a central mediator in the pathogenesis of diabetic nephropathy. Although high glucose levels stimulate catalytic activity of PKC, the effects of high glucose levels on the expression of genes encoding PKC isoforms are unknown. We sought to determine whether in addition to activation, diabetes may lead to increased transcription of two PKC isoforms that have been implicated in the pathogenesis of diabetic nephropathy, PKC-α and PKC-β.
Methods
Recent advances in molecular biological techniques now permit quantitative analysis of mRNA from archival, formalin-fixed, paraffin-embedded tissue sections. RNA was extracted from scraped 6 μm sections of biopsy tissue, and PRKC-α and PRKC-β (also known as PRKCA and PRKCB) mRNA measured using real-time PCR. Expression of genes encoding PKC isoforms was examined in renal biopsies (n = 25) with classical histological features of diabetic nephropathy and compared with that in normal control tissue (n = 6). Peptide localisation of PKC-α, PKC-β and the activated forms phosphorylated PKC-α and -β was also performed on matched paraffin-embedded sections of renal biopsies using immunohistochemistry. The effects of high glucose on PRKC-β expression and peptide production in cultured human proximal tubular epithelial cells were assessed.
Results
Quantitative real-time PCR demonstrated a 9.9-fold increase in PRKC-β mRNA in kidney biopsies of diabetic patients relative to control (p < 0.001). No increase in PRKC-α expression was seen. In addition, a correlation between renal PRKC-β mRNA and HbA1c was observed in diabetic patients (r = 0.63, p < 0.05). There was co-localisation of PKC-β and phospho-PKC-β predominantly to proximal tubules. A 60% increase in PRKC-β mRNA and peptide in cultured human proximal tubular epithelial cells exposed to high glucose (p < 0.05) was seen in vitro.
Conclusions/interpretation
PKC-β is upregulated at the gene expression level in human diabetic nephropathy. PRKC-β mRNA correlates closely with serum HbA1c, possibly partially explaining the relationship between glycaemic control and progression of diabetic nephropathy. Archival human tissue provides a valuable resource for molecular analyses.