PRKC-isoform mRNA expression in human kidney transplant protocol biopsies: is there a high-glucose-induced regulation in the diabetic state?

Abstract

Dear Sirs, Protein kinase C (PRKC) is a family of at least twelve serine–threonine kinases and a key signaling pathway in diabetic vascular complications [1]. Our group recently demonstrated that deletion of distinct PRKC isoforms in vivo prevents from diabetes-induced kidney damage, probably depending on the individual cell type or tissue, which subsequently interferes with experimental diabetic nephropathy through independent molecular mechanisms [1]. Data on renal PRKC transcript expression profiles in the early development of human diabetic kidney damage are, however, still missing. Therefore, the aim of this pilot study was to determine the transcript expression levels of renal PRKC isoforms a, b1, c, d, e, g, h, i by real-time quantitative PCR (qPCR) in three consecutive archival control kidney biopsies of diabetic transplant recipients and to compare to case-matched, non-diabetic controls. We retrospectively analyzed data from diabetic patients (n = 11) and case-matched, non-diabetic controls (n = 11) enrolled in the protocol biopsy program of the transplant center of the Hannover Medical School which is part of the routine medical care following kidney transplantation [2]. From these two study groups, RNA-later-embedded frozen biopsy samples collected 6 weeks (K1), 3 months (K2), and 6 months (K3) after kidney transplantation were subjected to PRKC-isoform-specific qPCR. The program had been approved by the local ethical committee and is conducted in accordance with the Declaration of Helsinki. The key findings of this pilot study were that although (1) the main PRKC isoforms (a, b1, e, f) are expressed early in human kidney transplants, (2) PRKC-isoform mRNA expression does not dynamically increase over time in a diabetic milieu in the first 6 months after kidney transplantation (Fig. 1). In contrast, we observed that (3) mRNA expression of the PRKC-f isoform was significantly decreased at time point 3 (K 3; 6 months after kidney transplantation) in the diabetic group compared to non-diabetic controls. Interestingly, previous observations many years ago showed that, in addition to PRKC activation through increased serine/threonine phosphorylation under hyperglycemic condition, high glucose also induces protein expression of PRKC-isoforms a, b, and e in mesangial cells after 48 h, but not after 12 h [3]. Toyoda et al. [4] suggested for the first time that elevated expression of PRKC–MAPK pathway mRNAs correlates with glomerular lesions in patients with overt diabetic nephropathy. Recently, Langham et al. [5] postulated that increased PRKC-b transcription measured by qPCR occurs in advanced human diabetic nephropathy by analyzing human kidney biopsies with longterm DM. In contrast to the latter study, our results did not show any significant up-regulation of any PRKC-isoform transcript expression using archival biopsy tissue within the first 6 months following human kidney transplantation in diabetic compared to non-diabetic recipients. We did not find a significant correlation between PRKC-isoform mRNA expression levels and HbA1c at the three distinct time points of biopsy. We also did not observe any relationship between PRKC-isoform mRNA expression and other laboratory or Communicated by Renato Lauro.