Interstitial Vascular Rarefaction and Reduced VEGF-A Expression in Human Diabetic Nephropathy

Abstract

Diabetic nephropathy (DN) is a frequent complication in patients with diabetes. Although the majority of DN models and human studies have focused on glomeruli, tubulointerstitial damage is a major feature of DN and an important predictor of renal dysfunction. This study sought to investigate molecular markers of pathogenic pathways in the renal interstitium of patients with DN. Microdissected tubulointerstitial compartments from biopsies with established DN and control kidneys were subjected to expression profiling. Analysis of candidate genes, potentially involved in DN on the basis of common hypotheses, identified 49 genes with significantly altered expression levels in established DN in comparison with controls. In contrast to some rodent models, the growth factors vascular endothelial growth factor A (VEGF-A) and epidermal growth factor (EGF) showed a decrease in mRNA expression in DN. This was validated on an independent cohort of patients with DN by real-time reverse transcriptase-PCR. Immunohistochemical staining for VEGF-A and EGF also showed a reduced expression in DN. The decrease of renal VEGF-A expression was associated with a reduction in peritubular capillary densities shown by platelet-endothelial cell adhesion molecule-1/CD31 staining. Furthermore, a significant inverse correlation between VEGF-A and proteinuria, as well as EGF and proteinuria, and a positive correlation between VEGF-A and hypoxia-inducible factor-1␣ mRNA was found. Thus, in human DN, a decrease of VEGF-A, rather than the reported increase as described in some rodent models, may contribute to the progressive disease. These findings and the questions about rodent models in DN raise a note of caution regarding the proposal to inhibit VEGF-A to prevent progression of DN.

Human Nephrosclerosis Triggers a Hypoxia-Related Glomerulopathy

“…The finding of glomerular VEGFA and FLT1 induction in NSC biopsy specimens is in contrast to the reduced expression of VEGFA recently reported in human diabetic nephropathy both in glomeruli and in the tubulointerstitial compartment, indicating a different pathophysiological mechanism for glomerulosclerosis in NSC and diabetic nephropathy. 33,45 HIF target genes involved in the accumulation of extracellular matrix and fibrosis were also found to be induced in glomeruli with NSC. This finding was confirmed by RT-PCR for FN1, for which HIF-independent regulatory mechanisms are also described, 46 and for LOXL2.…”

“…33 Predeveloped TaqMan reagents were used for human fibronectin 1 (FN1, NM_002026), human lysyl oxidase-like 2 (LOXL2, NM_002318.2), and the housekeeper genes 18S rRNA, GAPDH, and ␤-actin (Applied Biosystems, Foster City, CA). The following oligonucleotide primers (300 nmol/L) and probe (100 nmol/L) were used for human CXCR4 (NM_003467.2), sense primer 5Ј-GGCCGACCTC-CTCTTTGTC-3Ј, antisense primer 5Ј-CAAAGTACCAGTTT-GCCACGG-3Ј, and fluorescence labeled probe (FAM) 5Ј-ACGCTTCCCTTCTGGGCAGTTGATG-3Ј; and for CXCL12 (NM_199168), sense primer 5Ј-ACCGCGCTCTGCCTCA-3Ј, antisense primer 5Ј-CATGGCTTTCGAAGAATCGG-3Ј, and fluorescence labeled probe (FAM) 5Ј-TCAGCCT-GAGCTACAGATGCCCATGC-3Ј.…”

Hypoxia response and VEGF-A expression in human proximal tubular epithelial cells in stable and progressive renal disease

“…Recent publications also suggest a decline of VEGF-A expression in progressive diabetic nephropathy. 37 In a more general context, these findings are of significant importance because the expression of VEGF-A in the tubulointersititium is most likely to play a major role in neo-angiogenesis of peritubular capillaries, with reduced VEGF-A levels being responsible for peritubular capillary rarefaction, tubular atrophy, loss of functional nephrons, and impaired recruitment of endothelial progenitor cells. 23 The significance of these hypotheses is further supported by our results in which attenuated expression of VEGF-A and increased expression of HIF-1a together predicted outcome of chronic renal disease to a higher extent than well-established parameters, such as proteinuria, eGFR, or the degree of TAIF at the time of biopsy.…”

Vascular Endothelial Growth Factor Therapy for the Kidney

“…Major sources of renal VEGF are tubular epithelial cells and podocytes, whereas endothelial cells and podocytes (acting in both autocrine and paracrine fashions) are major targets. Recent studies showed that renal levels of VEGF are altered in pathologic situations, such as chronic and acute renal ischemia, 12,13 diabetic-induced renal injury, 14,15 atherosclerosis, 16 or metabolic syndrome, 17 suggesting a potential pathologic role of this cytokine to promote profound microvascular dysfunctional and morphologic changes. Elegant seminal studies by the laboratories of Johnson and colleagues 18 and Basile and colleagues 19 showed that VEGF therapy reduced renal damage and protected the microvasculature in rodent models of chronic renal disease.…”