Diabetes 57:2167-2175, 2008 DOI: 10.2337/db07-0780 © 2008 by the American Diabetes Association
Exposure to Maternal Diabetes Induces Salt-Sensitive Hypertension and Impairs Renal Function in Adult Rat Offspring
1 Institut National de la Santé et de la Recherche Médicale, Unite Mixte de Recherche S872, Centre de Recherche des Cordeliers, Paris, France; Université Paris Descartes, Unite Mixte de Recherche S872, Paris, France; Université Pierre et Marie Curie-Paris 6, Unite Mixte de Recherche S872, Paris, France Corresponding author: Martine Lelièvre-Pégorier, martine.lelievre-pegorier{at}crc.jussieu.fr
OBJECTIVE—Epidemiological and experimental studies have led to the hypothesis of fetal origin of adult diseases, suggesting that some adult diseases might be determined before birth by altered fetal development. We have previously demonstrated in the rat that in utero exposure to maternal diabetes impairs renal development leading to a reduction in nephron number. Little is known on the long-term consequences of in utero exposure to maternal diabetes. The aim of the study was to assess, in the rat, long-term effects of in utero exposure to maternal diabetes on blood pressure and renal function in adulthood. RESEARCH DESIGN AND METHODS—Diabetes was induced in Sprague-Dawley pregnant rats by streptozotocin on day 0 of gestation. Systolic blood pressure, plasma renin activity, and renal function were measured in the offspring from 1 to 18 months of age. High-salt diet experiments were performed at the prehypertensive stage, and the abundance of tubular sodium transporters was evaluated by Western blot analysis. Kidney tissues were processed for histopathology and glomerular computer-assisted histomorphometry. RESULTS AND CONCLUSIONS—We demonstrated that in utero exposure to maternal diabetes induces a salt-sensitive hypertension in the offspring associated with a decrease in renal function in adulthood. High-salt diet experiments show an alteration of renal sodium handling that may be explained by a fetal reprogramming of tubular functions in association or as a result of the inborn nephron deficit induced by in utero exposure to maternal diabetes.
Diabetes has recently assumed an epidemic proportion. Estimates suggest that worldwide, 30 million women of reproductive age will suffer from diabetes by 2030. Data from birth certificates indicate that some form of maternal diabetes complicates Fetal programming refers to the observation that an adverse environmental stimulus experienced in utero during the critical period of development of organogenesis can induce long-term effects on developing organism (10,11). These structural and functional effects predispose the offspring to several diseases in adulthood, i.e., hypertension and cardiovascular diseases. Many epidemiological studies have clearly confirmed the seminal works of Barker and Bagby (10), which evidenced the inverse relationship between a low birth weight as a marker of intrauterine stress and the risk of developing cardiovascular disease and hypertension. Brenner and colleagues (12) proposed that the inborn nephron deficit associated with this low birth weight predisposes offspring to impaired renal sodium excretion and to increased susceptibility to hypertension. More recently, several studies have also suggested a similar association between low birth weight and chronic kidney disease (12). We have previously shown that offspring of streptozotocin-induced diabetic rats have an impaired nephrogenesis with a reduction of 30% of nephron number (13–15). Our model is characterized by moderate levels of maternal hyperglycemia and by normal gestation and delivery with healthy pups without intrauterine growth retardation or congenital malformation. Therefore, the first aim of this work was to determine in our rat model whether maternal diabetes programs adult hypertension in the offspring and to address the implication of impaired renal sodium excretion in this process. The second aim of this study was to determine whether inborn nephron deficit alters renal function and to identify glomerular hypertrophy and injury as factors of progression of renal diseases.
Animals and nephron counting. Pregnant Sprague-Dawley rats, weighing 250–300 g, were made diabetic on day 0 of gestation by a single intraperitoneal injection of streptozotocin (Sigma, Saint Quentin-Fallavier, France) (35 mg/kg body weight in 0.4 mol/l citrate buffer, pH 4.5). The diabetic state was checked by measuring the plasma glucose concentration (Accuchek, Roche, France). Only pregnant females whose plasma glucose ranged between 15 and 20 mmol/l were included in the study. This diabetic status was confirmed every 2 days until delivery. As previously shown, this protocol results in a 30% reduction of the nephron number (13). On the day of delivery, the newborn rats were weighed. Each litter was then reduced to 10 pups. The present study was restricted to male offspring. All the animals were maintained in a temperature- and light-controlled room at 21°C with a 12-h light cycle. They had free access to food (UAR Laboratory, Villemoison sur Orge, France) and tap water. Seventy-six rats issued from 16 control mothers (control mother offspring) and 74 rats issued from 16 diabetic mothers (diabetic mother offspring) were used in this study. Six 1-month-old animals issued from three different litters of each group were removed, weighed, and prepared for nephron counting by acid maceration method as previously described (13). The remaining animals were followed from 1 to 18 months of life for blood pressure or for functional or histological renal evaluation. Some of them, seven and six rats issued from two different litters of control mother offspring and diabetic mother offspring groups, respectively, were followed after 18 months of life to determine the effect of in utero exposure to maternal diabetes on long-term survival. All experiments were conducted in accordance with the institutional guidelines and the recommendations for the care and use of laboratory animals put forward by the French Ministry of Agriculture.
Design of the experimental protocol from 1 to 18 months. Systolic blood pressure was measured during 3 successive days in conscious rats by a noninvasive method, tail-cuff plethysmography, using a blood pressure monitor (blood pressure recorder 8005 Narco BioSystems). Before the effective measurements, rats were trained by placing them in restrainers and pressing their tail several times. Blood pressure records were made several consecutives times on quiet animals in a silent ambience at constant temperature under a heating apparatus. Measurements were always performed by the same person. Renal function was estimated by creatinine clearance and proteinuria. For that purpose, rats were individually housed in metabolic cages (Techniplast, Exton, PA) with free access to food and demineralized water. After 3 days of adaptation, food and water intakes were measured every 24-h period, and the urine was collected throughout the protocol during 3 other consecutive days. Urine that was spontaneously excreted during each 24-h period was collected to determine daily urinary creatinine and sodium and protein excretions. At the end of the 3-day experimental study, blood samples were collected for creatinine and PRA measurements. Kidneys and hearts from 1- to 18-month-old control mother offspring and diabetic mother offspring rats were removed, weighed separately, and fixed with formalin for either histology or histomorphometry.
High-salt diet protocol.
Analytical procedures.
Histology.
Computer-assisted morphometric analysis.
Immunohistochemistry.
Preparation of membrane fractions and Western blot analysis.
Statistical analysis.
Gestational and delivery conditions and follow-up of rats exposed in utero to maternal diabetes. Glycemia of the 16 diabetic mothers was constant throughout gestation and fourfold higher than in the 16 controls (5.27 ± 0.34 vs. 21.6 ± 0.12 mmol/l). Gestation occurred normally, and the rats delivered spontaneously at term (21 days of gestation). The number of pups per litter was similar in both groups. At birth, pups appeared healthy with similar birth weight compared with controls. As previously described (13), in our model, in utero exposure to maternal diabetes induced nephron deficit in the offspring. At 1 month, the reduction of nephron number was 30% in rats issued from diabetic mothers compared with controls (35,133 ± 507 vs. 25,600 ± 570, respectively, P < 0.0001, n = 6 in each group). As shown in Table 1, mean body weight progressively increased with age and was similar in both groups from the newborn period until 3 months. However, at 6 and 12 months of age, it was significantly higher in the diabetic mother offspring group than in the control mother offspring group. Kidney and heart weights (relative to body weight) decreased as a function of age but were not significantly different in both groups. The same normal blood glucose levels were observed in control mother offspring and diabetic mother offspring groups (5.90 ± 0.23 vs. 5.61 ± 0.70 mmol/l in 6-month-old rats from both groups, n = 6 from three litters).
Effects of in utero exposure to maternal diabetes on blood pressure Systolic blood pressure. Rats exposed in utero to maternal diabetes demonstrated higher blood pressure in adulthood (Fig. 1). Although the systolic blood pressure of 1- and 3-month-old rats was similar in both groups, it was significantly increased from 6 months of age in diabetic mother offspring compared with control mother offspring. Hypertension lasted and further increased during the observation period.
PRA and RRE. PRA and RRE are given in Table 2. At the prehypertensive stage (1- and 3-month-old rats), PRA and RRE were not significantly different in the two groups. From 6 months of age (hypertensive stage), a significant decrease of PRA was observed in diabetic mother offspring, when compared with their respective age-matched control mother offspring. With aging, the reduction of PRA and RRE was present in both groups.
Effect of high-salt diet on blood pressure and urinary sodium excretion. To study the response to a chronic alteration in sodium balance, both groups of rats were given a high-salt diet (3% NaCl diet instead of 0.3%) (Fig. 2). Means of the 24-h diet intake for the 3 days of sodium excretion measurement were similar in the two groups (28.32 ± 0.83 vs. 28.03 ± 1.1 g in control mother offspring and diabetic mother offspring group, respectively).
Systolic blood pressure was similar in the two groups on normal-sodium diet (0.3%). High-salt diet (3%) induced a raise of systolic blood pressure in the diabetic mother offspring group (respectively, 131.7 ± 0.8 vs. 154.5 ± 3.2 mmHg; paired t test, P < 0.01) and had no effect on blood pressure in the control mother offspring group. As expected, high-sodium diet led to a significant increase of urinary sodium excretion in both groups. However, this increase was significantly delayed in diabetic mother offspring compared with control mother offspring, accounting for a larger positive sodium balance.
Effect of high-salt diet on relative abundance of renal sodium transporters.
Finally, the protein levels of NHE3 and NCC were not different in diabetic mother offspring receiving a high-salt diet compared with control mother offspring either in the cortex or in the medulla.
Renal effects of in utero exposure to maternal diabetes
Glomerulus histomorphometry. To address the question of a structural glomerular adaptation to the reduction of nephron number, a glomerular histomorphometry study was performed in kidneys taken from 1- to 18-month-old control mother offspring and diabetic mother offspring rats (Fig. 4). In each age-group, no significant differences were observed between glomeruli measured in either superficial or deep cortex areas between control mother offspring and diabetic mother offspring kidney rats (data not shown). TGA significantly increased with advancing age. TGA was not significantly different between the two groups, although it was transitorily increased in 6-month-old diabetic mother offspring rats. TCL was significantly increased in the 6-month-old diabetic mother offspring compared with the control mother offspring. TCL/TGA was similar in both groups. At 18 months of age, TMA and TMA/TGA were similar in diabetic mother offspring and control mother offspring groups.
Renal histopathology. Renal histopathology was assessed in 1- to 18-month-old control mother offspring and diabetic mother offspring rats. Before 18 months of age, all kidneys were normal and devoid of glomerulosclerosis and interstitial fibrosis (data not shown). At 18 months of age, renal lesions were limited to focal areas of interstitial fibrosis with minimal tubular atrophy and to very few glomeruli with segmental glomerulosclerosis (Fig. 5A and B). Semiquantitative analysis showed that the extent of both glomerulosclerosis (glomerulosclerosis index: control mother offspring, 10.08 ± 1.62, n = 13 rats from three different litters vs. diabetic mother offspring, 8.49 ± 1.91, n = 9 rats from two different litters; unpaired t test; NS, arbitrary units) and tubulointerstitial lesions (Interstitial fibrosis index: control mother offspring, 5.12 ± 1.69, n = 8 rats from two different litters vs. diabetic mother offspring, 7.80 ± 4.25, n = 5 rats from three different litters; unpaired t test; NS, arbitrary units) were not different in the two groups.
Survival study. Survival study showed an increased mortality after 18 months of age in diabetic mother offspring. At 23 months, long-term survival was markedly reduced in the diabetic mother offspring group, 33.3% compared with 85.7% in the control mother offspring group. We therefore decided to kill the remaining rats to address late kidney histopathology in rats of the two groups. A widespread interstitial fibrosis with tubular atrophy and dilatation was present in the kidneys of diabetic mother offspring rats, associated with glomerulosclerosis and glomerular cysts. A scarce interstitial fibrosis and tubular atrophy was present in control mother offspring rats (Fig. 5C–F). Glomerulosclerosis index is 7.25 ± 3.50, n = 6, in control mother offspring versus 87 and 66 in two diabetic mother offspring rats, and interstitial fibrosis index is 27.5 ± 24.3, n = 6, in control mother offspring versus 230 and 300 in two diabetic mother offspring rats. No structural changes in the intra-renal vessels were observed at any age.
The present study identifies the long-term consequences of in utero exposure to maternal diabetes in the rat and shows that in utero exposure is associated with the development of a salt-sensitive systolic hypertension and with a decrease in renal function in adulthood. A mild to moderate increase in systolic arterial blood pressure is observed in the offspring of diabetic mothers from 6 months of age, which progressively went worse with the age. This rise in blood pressure is associated with low PRA, suggesting a salt-sensitive hypertension. We further confirmed the salt sensitivity with high-sodium diet experiments performed at prehypertensive stage: in diabetic mother offspring rats, a high-sodium diet induced an increase of systolic blood pressure and led to a shift to the right of the urinary sodium excretion curve, indicating a delayed sodium excretion. A similar salt-sensitive hypertension has been reported in a neonatal uni-nephrectomized rat model by Woods et al. (22). Together, these results are in accordance with the hypothesis of Brenner et al. (23), which states that inborn nephron deficit predisposes reduced renal sodium excretion, leading to hypertension susceptibility, especially in the setting of dietary sodium excess. Interestingly, in inbred rat models of hypertension, the relationship between nephron number and blood pressure is still a matter of debate (24–26). In addition, recently, Rocha et al. (8) and Magaton et al. (9) reported hypertension in rats issued from diabetic mothers without inborn nephron deficit. However, their model slightly differs from ours: 1) The level of maternal hyperglycemia is more pronounced in our model (we have previously shown that inborn nephron deficit correlated with the level of maternal hyperglycemia [13]); and 2) we performed direct glomerular counting with the gold-standard acid-maceration method, whereas they used an histological-derived method that is more appropriate to evaluate the density of glomeruli.
Because one mechanism involved in such renal sub-optimal sodium handling may traduce a resetting of tubular sodium cotransporter expression, we then evaluated the protein abundance of Na transporters and channels in the kidney at the prehypertensive stage and under a high-salt diet. In the cortex of diabetic mother offspring rats, we found an increase of three different sodium transporter proteins: βENaC, In the present study, we also show that maternal diabetes is associated with a decreased renal function in adulthood, as assessed by creatinine clearance and proteinuria measurements. According to Brenner and colleagues (12,23), a compensatory glomerular hypertrophy and hyperfiltration occur in response to inborn nephron deficit to sustain adequate renal function. Such glomerular adaptation made at the expense of intraglomerular hypertension accelerates injury to the remaining functional glomeruli and perpetuates the ongoing glomerulosclerosis, leading to renal failure. However, in our model in which inborn nephron deficit is observed, systematic analysis of renal histology shows that both glomerulosclerosis and interstitial fibrosis are absent in diabetic mother offspring and control mother offspring groups at all stages before 18 months of age. At 18 months, because of aging (17), mild renal structural lesions occur but at the same extent in the two groups. In addition, glomerular computer-assisted histomorphometry shows a mild glomerular hypertrophy only at 6 months, at the onset of hypertension in diabetic mother offspring rats. In our model, absence of early increase of glomerular size and of sustained glomeruli hypertrophy with aging does not support a major glomerular adaptation to the inborn nephron deficit. Together, these two sets of results seem to weight against a compensatory glomerular hypertrophy and hyperfiltration as factors of alteration and worsening of the renal function until 18 months of age. Concerning the study of Rocha et al. (8), one must note that although decreased nephron number was not observed in young animals, the number of nephrons was reduced at 12 months in diabetic mother offspring rats. However, because no histological data were provided in their study to evaluate the extent of glomerulosclerosis, the mechanisms of ongoing nephron loss and its implication in the decline of renal function has not been elucidated in their model. In the other hand, a dramatic impairment of renal histology with widespread glomerular and tubulo-interstitial lesions was observed in kidneys issued from 23-month-old diabetic mother offspring rats. Such late alterations of kidney structures compared with the early impairment of renal function could hardly be explained by the consequences of a congenital nephron deficit alone. The link between the congenital nephron deficit and the adverse effect of compensatory hyperfiltration on the remaining glomeruli leading to glomerulosclerosis has been unambiguously demonstrated (and quantitatively assessed) in models with severe reduction in the nephron number or in models with toxic renal impairment that associates both in utero glomerular reduction and tubulo-interstitial lesions (30,31). In our present model, the mild (30%) congenital nephron deficit might not be sufficient per se to induce glomerular lesions, at least during the first 18 months of life. Another issue to consider is the kidney as a target organ of hypertension. In our model, although hypertension is present from 6 months of age, high level of systolic blood pressure is only achieved at 18 months. It is well known that the increase of blood pressure is limited and slowly increases with age in the majority of the model of perinatal programming of hypertension compared with other rat models of hypertension (32,33). This may explain why we observe the histopathological renal consequences of hypertension only in the 23-month-old rats. However, the implication of hypertension alone in the renal lesions of our model is questionable, because even at 23 months, intra-renal vascular hypertensive lesions are nearly absent at histology, and myocardial (other target organ of hypertension) histology is similar in both groups (data not shown). This study thus identifies maternal diabetes as a novel risk factor for fetal programming of adult hypertension and impairment of renal function. Alteration of renal sodium handling, observed in our model, may be explained by a fetal resetting of tubular functions, as a consequence or in association with congenital nephron deficit.
This work was supported by a grant from the Institut National de la Recherche Medicale. We acknowledge the technical assistance of Marie-France Belair and Martine Douheret (Institut National de la Santé et de la Recherche Médicale, Unite Mixte de Recherche S872, Centre de Recherche des Cordeliers). We also acknowledge the technical assistance of Michele Smirnoff for animal nursing and of Nelly Knobloch for secretarial assistance. Parts of this work were presented in abstract form at the 38th annual meeting of the American Society of Nephrology, Philadelphia, Pennsylvania, 8–13 November 2005.
Published ahead of print at http://diabetes.diabetesjournals.org on 28 April 2008. T.N. and J.-P.D.V.H. contributed equally to this work. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received for publication June 8, 2007 and accepted in revised form April 20, 2008
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