Kuniko Kimura

Hypoxia promotes fibrogenesis in vivo via HIF-1 stimulation of epithelial-to-mesenchymal transition

Hypoxia has been proposed as an important microenvironmental factor in the development of tissue fibrosis; however, the underlying mechanisms are not well defined. To examine the role of hypoxia-inducible factor-1 (HIF-1), a key mediator of cellular adaptation to hypoxia, in the development of fibrosis in mice, we inactivated Hif-1alpha in primary renal epithelial cells and in proximal tubules of kidneys subjected to unilateral ureteral obstruction (UUO) using Cre-loxP-mediated gene targeting. We found that Hif-1alpha enhanced epithelial-to-mesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1alpha inhibited the development of tubulointerstitial fibrosis in UUO kidneys, which was associated with decreased interstitial collagen deposition, decreased inflammatory cell infiltration, and a reduction in the number of fibroblast-specific protein-1-expressing (FSP-1-expressing) interstitial cells. Furthermore, we demonstrate that increased renal HIF-1alpha expression is associated with tubulointerstitial injury in patients with chronic kidney disease. Thus, we provide clinical and genetic evidence that activation of HIF-1 signaling in renal epithelial cells is associated with the development of chronic renal disease and may promote fibrogenesis by increasing expression of extracellular matrix-modifying factors and lysyl oxidase genes and by facilitating EMT.

Hypoxia-inducible factor signaling in the development of tissue fibrosis.

Capillary rarefaction is a hallmark of fibrotic diseases and results in reduced blood perfusion and oxygen delivery. In the kidney, tubulointerstitial fibrosis, which leads to the destruction of renal tissue and the irreversible loss of kidney function, is associated with hypoxia and the activation of Hypoxia-Inducible-Factor (HIF) signaling. HIF-1 and HIF-2 are basic-helix-loop-helix transcription factors that allow cells to survive in a low oxygen environment by regulating energy metabolism, vascular remodeling, erythropoiesis, cellular proliferation and apoptosis. Recent studies suggest that HIF activation promotes epithelial to mesenchymal transition (EMT) and renal fibrogenesis. These findings raise the possibility that the spectrum of HIF activated biological responses to hypoxic stress may differ under conditions of acute and chronic hypoxia. Here we discuss the role of HIF signaling in the pathogenesis and progression of chronic kidney disease.

Epithelial-Mesenchymal Transition as a Potential Explanation for Podocyte Depletion in Diabetic Nephropathy

BACKGROUND Depletion of glomerular podocytes is an important feature of progressive diabetic nephropathy. Although the most plausible explanation for this podocyte depletion is detachment from the glomerular basement membrane after cellular apoptosis, the mechanism is unclear. Fibroblast-specific protein 1 (FSP1; encoded by the S100A4 gene) is a member of the S100 family of calcium-binding proteins and is constitutively expressed in the cytoplasm of tissue fibroblasts or epithelial cells converted into fibroblasts by means of epithelial-mesenchymal transition. STUDY DESIGN Retrospective cross-sectional analysis. SETTINGS & PARTICIPANTS 109 patients with type 2 diabetes mellitus, of whom 43 (39%) underwent kidney biopsy. PREDICTOR Clinical stage (4 categories) and histological grade (5 categories) of diabetic nephropathy. OUTCOME FSP1 expression in podocytes in urine and glomeruli in kidney biopsy specimens. MEASUREMENTS Immunohistochemistry, real-time polymerase chain reaction, and in situ hybridization. RESULTS 38 of 109 patients (35%) were normoalbuminuric, 16 (15%) had microalbuminuria, 8 (7%) had macroalbuminuria, and 47 (43%) had decreased kidney function. Approximately 95% of podocytes in urine sediment were not apoptotic, and 86% expressed FSP1. The number of FSP1-positive podocytes in urine sediment was significantly larger in patients with macroalbuminuria than in those with normoalbuminuria (P = 0.03). Intraglomerular expression of FSP1 occurred almost exclusively in podocytes from patients with diabetes, and the number of FSP1-positive podocytes was larger in glomeruli showing diffuse mesangiopathy than in those showing focal mesangiopathy (P = 0.01). The number also was larger in glomeruli with nodular lesions than in those without nodular lesions (P < 0.001). FSP1-positive podocytes selectively expressed Snail1 and integrin-linked kinase, a known trigger for epithelial-mesenchymal transition. LIMITATIONS Nonrepresentative study population. CONCLUSIONS These results suggest that the appearance of FSP1 in podocytes of patients with diabetes is associated with more severe clinical and pathological findings of diabetic nephropathy, perhaps because of induction of podocyte detachment through epithelial-mesenchymal transition-like phenomena.

Beta-cell function and insulin sensitivity contribute to the shape of plasma glucose curve during an oral glucose tolerance test in non-diabetic individuals.

To clarify whether beta‐cell function and/or insulin resistance contributes to the shape of plasma glucose curve during an oral glucose tolerance test (OGTT), we investigated 583 Japanese subjects with normal glucose tolerance (NGT, n = 306) or impaired glucose tolerance (IGT, n = 277). Each subject was subdivided into three shapes of plasma glucose curve as follows: monophasic pattern (M type), biphasic pattern (B type) and two peaks (T type). Homeostasis model assessment of insulin resistance, quantitative insulin sensitivity check index and insulinogenic index were assessed by plasma glucose and insulin concentrations obtained at fasting or during an OGTT. There was a greater proportion of M type in the IGT group (M = 80.9%, B = 15.5% and T = 3.6%), whereas the prevalence of B and T types was much higher in the NGT group (M = 66.6%, B = 26.5% and T = 6.9%). There were significant differences in the proportions of shape types between the NGT and IGT groups (p = 0.0006). Among the NGT category, insulin sensitivity was significantly higher in the B type than in the M type, and beta‐cell function adjusted for insulin resistance was significantly higher in the B and T types than in the M type. Among the IGT category, no significant differences were seen among the three shape types with respect to insulin sensitivity, but the beta‐cell function adjusted for insulin resistance was significantly lower in the M type than in the B and T types. In conclusion, both impaired insulin secretion and insulin resistance may contribute to the underlying mechanisms of the shape of plasma glucose curve in Japanese subjects.

Prediction of corticosteroid responsiveness based on fibroblast-specific protein 1 (FSP1) in patients with IgA nephropathy

BACKGROUND Corticosteroids are frequently used to treat patients with active IgA nephropathy (IgAN); however, there have been few reports describing factors that are predictive of the response to corticosteroid treatment. The purpose of this study is to determine the extent to which fibroblast-specific protein 1-positive (FSP1(+)) cells are predictive of corticosteroid responsiveness in patients with IgAN. METHODS Fifty biopsy-proven IgAN patients who received corticosteroid therapy were enrolled and followed for 7.1 +/- 3.0 years. FSP1(+) cells were identified using an anti-FSP1 antibody. RESULTS Twelve patients showed progression of renal impairment or no reduction of urinary protein (non-responders) after steroid therapy. In the remaining 38 patients, renal function was stable during follow-up, and their urinary protein declined to <1.0 g/day (responders). Serum creatinine, estimated GFR, severity of mesangial proliferation, percent glomerulosclerosis/total glomeruli, extent of interstitial damage and FSP1(+) cell number were all significantly higher in non-responders than in responders. Cox regression analysis using two covariates with every possible combination of factors indicated that FSP1(+) cell number was the strongest and most significant predictor of corticosteroid responsiveness. When IgAN patients had >32.6 FSP1(+) cells/HPF at diagnosis, they were the more likely to show steroid resistance. CONCLUSION FSP1(+) cell number can serve as an excellent predictor of corticosteroid responsiveness in patients with IgAN.

Surrogate markers of insulin resistance in assessing individuals with new categories “prehypertension” and “prediabetes”

Abstract Background: There are few data on the impact of insulin resistance on the recently defined categories of prehypertension (PHT) and prediabetes (PDM). The aim of this study was to examine associations of surrogate markers of insulin resistance with PHT/PDM. Methods: Subjects included 554 individuals who underwent a 75-g oral glucose tolerance test (OGTT). They were classified into four groups using a severity score for high blood pressure and glucose tolerance. Insulin resistance was measured using the homeostasis model assessment of insulin resistance (HOMA-R) and three surrogate markers obtained from 75-g OGTT values (ISI-composite, Stumvoll index, and OGIS index). Results: HOMA-R increased significantly, but the other three surrogate indices decreased with increasing severity score. Of these markers, the OGIS index was mostly associated with prevalent PHT/PDM and the odds ratio for insulin resistance was 3.61 (95% CI 1.68–7.76, p=0.001) for subjects with either PHT or PDM and 29.98 (12.81–70.18, p<0.001) for subjects with both PHT and PDM. Conclusions: PHT and PDM frequently coexist in relatively lean Japanese subjects. Decreased insulin sensitivity may contribute to the underlying status of PHT/PDM. Among the surrogate markers of insulin resistance, the OGIS index is the most sensitive for assessment of PHT/PDM status. Clin Chem Lab Med 2007;45:35–9.

Preexisting Essential Hypertension Accelerates the Development of Diabetic Renal Lesions in Early Stage Nephropathy

Accessible online at: www.karger.com/journals/nef Dear Sir, Kidney is one of the principal target organs of essential hypertension (EHT), and an increased urinary albumin excretion is often found in patients with EHT [1]. It has been also shown in Pima Indians that higher prediabetic blood pressures predict an abnormal urinary excretion of albumin after the onset of diabetes [2]. We hypothesized that preexisting EHT before the onset of diabetes might initiate the subsequent development of diabetic glomerulosclerosis. Thirtynine patients with type 2 diabetes (26 males and 13 females) who underwent renal biopsy within 5 years of the detection of diabetes were studied. All patients gave their informed consent. Of these patients, 24 had preexisting EHT (group EHT; mean duration of hypertension 9.7 B 7.5 years), and 15 had no hypertension (group NT). The severity of glomerular lesions was estimated by quantitative morphometric studies using light microscopy [3]. Briefly, periodic acidSchiff (PAS)-stained specimens were analyzed using a color image processor (SPICCA-II, Olympus Co., Tokyo, Japan) measuring glomerular area (GA) and mesangial ratio (MR%). GA was defined as inner area of glomerular tuft outline, and MR% was defined as the ratio of PAS-positive area to total GA. The severity of the tubulointerstitial lesions (TIL%) was determined by a semiquantitative estimate of the space occupied by the fibrous tissue and/or interstitial infiltrates. Arteriolo-sclerosis score was graded as 0 (normal), 1 + (mild), 2+ (moderate), or 3+ (severe). There was no significant difference in age at onset of diabetes (NT 54.1 B 7.6 vs. EHT 55.1 B 7.1 years), time interval between diagnosis of diabetes and renal biopsy (1.67 B 1.63 vs. 2.04 B 1.92 years), age at time of renal biopsy (55.7 B 7.4 vs. 57.2 B 6.8 years), serum creatinine (0.67 B 0.15 vs. 0.74 B 0.20 mg/dl), or HbA1c (8.09 B 1.91 vs. 7.20 B 1.90%) between the two groups. Urinary albumin excretion rate, MR%, TIL% and arteriolosclerosis score were significantly higher in group EHT than in group NT (table 1). In summary, the presence of essential hypertension before the onset of type 2 diabetes accelerates the development of diabetic renal lesions even in the early stage nephropathy. References