![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Departamento de Fisiologia e Biofísica e
*
Departamento de Histologia e Embriologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, SP, Brasil;
Departamento de Patologia Geral, Faculdade de Medicina do Triângulo Mineiro, Uberaba, MG, Brasil; e
**
Departamento de Nutrição e Dietética, Faculdade de Enfermagem e Nutrição, Universidade Federal de Mato Grosso, Cuiabá, Brasil
2To whom correspondence should be addressed. E-mail: boschero{at}unicamp.br.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
KEY WORDS: • pancreatic islets • low protein diet • insulin secretion • islet size • rats
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). In rapidly growing organisms, malnutrition in early life is a serious challenge to which the system tries to adjust. The quantity and/or quality of nutrition in this critical period has permanent consequences for later life. One of the mechanisms of adaptation to an inadequate supply of nutrients is to slow down the rate of cell division in tissues and organs, which may lead to altered "programming" of the structure and function of the system (2
–4
).
Based on epidemiologic evidence, malnutrition has been envisaged as an etiological and/or a precipitating factor for diabetes in malnourished individuals in developing countries (5
,6
). The prevalence of type 2 diabetes is much higher in adults with a low weight at birth (7
), and malnutrition is associated with impaired insulin secretion (8
). Alteration in the maternal metabolic milieu during pregnancy influences the development and functional maturation of B cells (9
). Fetal malnutrition in rat pups results in a reduced number of B cells, a diminution in the proliferation of islet cells, reduced islet size and a marked decrease in islet vascularization (10
).
Glucose homeostasis in mammals requires the proper regulation of insulin secretion from pancreatic B cells. The primary signal for secretion is an elevation in blood glucose concentrations that induces the release of stored insulin. Glucose also regulates the transcription (11
–14
) and translation (15
–18
) of preproinsulin (PPI)3
and stabilizes PPI mRNA (19
). However, the mechanisms by which glucose influences the expression of the PPI gene are less well understood than those that control insulin secretion acutely.
The 5' flanking region of the PPI gene has been studied extensively and a number of important regulatory elements and trans-acting factors have been identified (20
). One of these factors is the homeodomain transcription factor pancreatic duodenal homeobox-1 (PDX-1), which plays an important role in lineage determination in the developing endocrine pancreas (20
,21
). In addition, PDX-1 transactivates insulin, glucose transporter isoform 2 (GLUT-2), glucokinase and somatostatin genes (22
). There is strong evidence supporting a role for PDX-1 in the mechanism by which glucose stimulates insulin gene transcription (23
–25
). Glucose stimulates the conversion of PDX-1 from a 31-kDa unphosphorylated to a 46-kDa phosphorylated form in human isolated islets. In B cells, this event appears to be dependent on insulin signaling via the phosphatidylinositol 3-kinase pathway (26
).
In this study, we evaluated the insulin secretion, islet size and PDX-1 expression in islets from rats fed a protein-deficient diet during gestation and lactation, and examined the influence of nutritional recovery on these variables.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
The animal experiments were approved by the institutional (UNICAMP) Committee for Ethics in Animal Experimentation. Virgin female Wistar rats (80–90 d old) were obtained from the breeding colony at UNICAMP. Mating was done by housing females with males overnight, and pregnancy was confirmed by examining vaginal smears for the presence of sperm. Pregnant females were separated at random and fed from d 1 of pregnancy until the end of lactation an isoenergetic diet containing 6% protein (low protein diet, LP) or 17% protein (control diet). The protein in the LP diet was replaced by the same amount of carbohydrate as described previously (27
). Some of the control and LP diet rats were killed at birth to determine immunohistochemistry. The remaining rats were assigned to three groups: 1) a control group (C) consisting of rats born to and suckled by dams fed a control diet during pregnancy and lactation; 2) an LP group consisting of the offspring of dams fed a LP diet during both pregnancy and lactation; and 3) a recovered group (R) consisting of the offspring of dams fed the LP diet during pregnancy but fed the control diet during lactation. During the experimental period, the dams consumed their respective diets ad libitum and had free access to water. The rats were housed under standard lighting (12-h light:dark cycle) at a temperature of 24°C. At the end of the experimental period (28 d of life), the rats were killed by decapitation. Serum glucose (glucose enzymatique kit, Biotrol Diagnostic, Chennevières, France) and free fatty acids (Nonesterified Fatty Acid C kit, Wako Chemicals GmbH, Neuss, Germany) were measured immediately. Part of the serum was stored at -20°C for the subsequent measurement of insulin by RIA (28
).
Insulin secretion.
Islets were isolated by collagenase digestion. Briefly, the pancreas was inflated with Hanks solution containing 0.7–0.9 g collagenase/L, excised and then maintained at 37°C for 20 min. The digested tissue was harvested and the islets were handpicked. Groups of five islets were first incubated for 45 min at 37°C in 0.5 mL of Krebs-bicarbonate buffer of the following composition (mmol/L): NaCl, 115; KCl, 5; CaCl2, 2.56; MgCl2, 1; NaHCO3, 24; and glucose, 5.6, supplemented with 3 g/L bovine serum albumin and equilibrated with a mixture of 95%O2/5%CO2, pH 7.4. This medium was then replaced with fresh buffer and the islets incubated for 90 min in the presence of 2.8 or 16.7 mmol/L glucose. The insulin in the medium at the end of the incubation period was measured by RIA (28
).
Morphometry and immunohistochemistry.
The pancreata were excised and dissected free of surrounding tissues, weighed and fixed by immersion in 10% formaldehyde-PBS solution. The fixed tissue was embedded in paraffin using a standardized protocol, then cut in 6-µm thick sections and mounted on glass slides. The sections were counterstained with hematoxylin-eosin for morphometric analysis. The islet area was measured by planimetry using a MOP-Videoplan image analysis software (Kontron Eletronik, Munich, Germany). The sectional area of islets was measured at a magnification of 40X.
Every 10th section from each pancreas was deparaffinized, rehydrated and heated in 10 mmol/L citrate buffer (pH 6.0) at 92°C for 10 min in a microwave oven for antigen retrieval. After cooling at room temperature, the sections were washed three times with PBS, and endogenous peroxidase was blocked by a 30-min incubation with 3% H2O2 at room temperature. For PDX-1 immunohistochemistry, sections were incubated overnight at 4°C with polyclonal rabbit anti-PDX-1 antibody diluted 1:1000. Detection was with a streptavidin-biotin-peroxidase complex developed with aminoethylcarbazol (Zymed, San Francisco, CA). As a negative control, liver slices underwent similar treatment, and no positive reactions to the antibody against PDX-1 were observed (not shown).
Western blot.
After isolation by collagenase digestion of pancreata and subsequent separation on discontinuous lyophilized Ficoll DL-400 gradients, a pool of at least 1000 clean islets from each experimental group was homogenized by sonication (15 s) in an anti-protease cocktail (10 mmol/L imidazole, pH 8.0, 4 mmol/L EDTA, 1 mmol/L EGTA, 0.5 mg/L pepstatin A, 2 mg/L aprotinin, 2.5 mg/L leupeptin, 30 mg/L trypsin inhibitor, 200 µmol/L DL-dithiothreitol and 200 µmol/L phenylmethylsulfonyl fluoride. After sonication, an aliquot of extract was collected and the total protein content was determined by the dye-binding protein assay kit (Bio-Rad Laboratories, Hercules, CA). Samples of crude membrane preparations from each experimental group containing 70 µg of protein were incubated for 5 min at 80°C with 5X concentrated Laemmli sample buffer (1 mmol/L sodium phosphate, pH 7.8, 0.1% bromophenol blue, 50% glycerol, 10% SDS, 2% mercaptoethanol) (4:1, v/v). The samples were then run on 10% polyacrylamide gels. Electrotransfer of proteins to nitrocellulose membranes (Bio-Rad) was done for 1 h at 120 V (constant) in buffer containing methanol and SDS. After checking the efficiency of transfer by Ponceau S staining, the membranes were blocked with 50 g/L dry skimmed milk in TTBS (10 mmol/L Tris, 150 mmol/L NaCl, 0.5% Tween 20) overnight at 4°C. PDX-1 was detected in the membrane after a 2-h incubation at room temperature with a rabbit polyclonal antibody against PDX-1 (diluted 1:2500 in TTBS plus 30 g/L dry skimmed milk). The membrane was then incubated with a rabbit anti-mouse immunoglobulin G (diluted 1:1500 in TTBS plus 30 g/L dry skimmed milk) followed by a further 2-h incubation at room temperature with I125-labeled protein A (diluted 1:1000 in TTBS plus 10 g/L dry skimmed milk). Radiolabeled protein bound to the antibody was detected by autoradiography. Band intensities were quantified by optical densitometry (Scion Image, Frederick, MD) of the developed autoradiogram.
mRNA expression.
Total RNA from 400 islets, isolated and separated as described for Western blot analysis, was extracted using TriZol reagent (Life Technologies, Auckland, New Zealand). For polymerase chain reaction (PCR) analysis, RNA (2 µg) was reverse-transcribed using oligo(DT) primers. The resulting cDNA were amplified by PCR using oligonucleotides complementary to sequences in the PDX-1 gene (5'-CCGAATGGAACCGAGACTGG-3' and 5'-AGGTGGTGGCTTTGGCAATG-3') and phospholipase A2 gene (5'-CTGCTGGCTGCTTTGCTCAC-3'and 5'-ACGGCATAGACAGGAAGTGGG-3'), with the latter as the internal control. The PCR was done in a 25-µL reaction volume containing 1 µL cDNA, 0.05 mmol/L each cold dNTP (dATP, dCTP, dGTP, dTTP), 0.37 mmol/L MgCl2, 0.25X PCR buffer, 0.1 µmol/L of appropriate oligonucleotides primers, and 1 U Taq polymerase (Life Technologies). The PCR amplification conditions for PDX-1 were as follows: 3 min at 94°C followed by 29 cycles (30 s each) at 94, 59 and 72°C, and for phospholipase A2 (internal control), 2 min at 94°C followed by 25 cycles (30 s each) at 94, 58 and 72°C. Because actin was altered in LP islets, it was not used as an internal control. The PCR products were separated on a 1.5% agarose gel in Tris borate EDTA buffer 1X (TBE 1X) and stained with ethidium bromide. All PCR included a negative control. The absence of genome contamination in the RNA samples was confirmed by the reverse transcription–negative RNA samples. The relative band intensities were determined by densitometry and the ratio of PDX-1 to phospholipase A2 was calculated for each sample.
Statistical analysis.
The results were expressed as means ± SEM. Student’s two-tailed unpaired t test was used to compare the normal (C) and LP groups at birth. Levene’s test for homogeneity of variances was initially used to check the normality of the data before testing with parametric ANOVA. One-way ANOVA was used to compare the body and pancreas weights, serum glucose, insulin and FFA levels, islet areas and aggregates positive for PDX-1 in the C, LP and R groups at 28 d of life. Two-way ANOVA followed by the Bonferroni’s test was used to evaluate differences in insulin secretion. A two-way frequency table (29
) was used to verify whether the distribution of islet size was affected by protein deprivation and by nutritional recovery. A P-value < 0.05 indicated a significant difference. All statistical analyses were done using the Statistica software package (Statsoft, Tulsa, OK).
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
At birth, pups from dams fed the LP diet during pregnancy had lower body and pancreas weights than control pups. The serum glucose but not insulin level was reduced, whereas serum FFA were higher than in control pups. After 28 d, LP rats had lower body and pancreas weights, reduced serum glucose and insulin levels, and greater serum FFA concentrations than C and R rats (P < 0.001). Except for body and pancreas weights, which were higher than in C rats (P < 0.001), all variables were normalized in the R pups (Table 1
).
|
Insulin secretion in the presence of 2.8 and 16.7 mmol glucose/L was lower in islets from LP pups than in those from controls (P < 0.05). In islets from R pups, secretion was restored to values not different from those in controls (Fig. 1
).
|
At birth, the area of islets from LP rats was significantly lower than C rats (P < 0.0001). After weaning, the area of islets from C and R rats did not differ but was still reduced in LP rats (P < 0.001 LP vs. C and R) (Table 2
). Newborn LP rats had 71% of islets with the lowest size class (<4000 µm2), whereas C rats had 31% islets of intermediate size (4000–8000 µm2) and 21% of the highest (>8000 µm2) size class (G = 32.04; df = 2; P < 0.001). In weaned rats (C vs. R groups: G = 1.75, df = 2, P = 0.42; C vs. LP groups: G = 28.2, df = 2, P < 0.001; R vs. LP groups: G = 34.17, df = 2, P < 0.001), the frequency of the lowest size class (<5000 µm2) was not different in R (44%) and C (49%) groups, and was lower than in the LP pups (74%). The frequency of both intermediate (5000–10,000 µm2) and highest (>10,000 µm2) size classes in R rats (36 and 21%, respectively) did not differ from that of C rats (35% and 16%, respectively). In both cases, these were higher than in the LP group (18 and 8%, respectively).
|
PDX-1 expression in islets from 28-d-old C, LP and R rats was analyzed by immunoblotting using a polyclonal anti-PDX-1 antibody (Fig. 2
). A 46-kDa protein representing PDX-1 was detected in all three tissue extracts. Densitometry of the bands showed that the amount of PDX-1 in the extract from LP islets was 
50% lower than in extracts from C and R islets (P < 0.01). The presence of PDX-1 in B cells was confirmed by immunocytochemistry. PDX-1 labeling was located in the nucleus of the islet cells and showed a bright, interspersed pattern within the nucleus (Fig. 3
, upper panels). The number of positive cells for PDX-1 was higher in islets from control than LP diet pups on d 1 (Fig. 3
A, B). PDX-1 labeling was also detected in pancreatic duct cells (Fig. 3
A). Figure 3
(C–E) shows that PDX-1 expression in islets from 28-d-old LP rats (D) was lower than in islets from C rats (C) and was normalized in islets from R rats (E). The number of aggregates positive for PDX-1 (Table 2)
in islets from LP pups was 20% of that in islets from controls at birth and after weaning (P < 0.05). The number of positive aggregates in R islets was not different from that in C islets. The positive aggregates represent, in fact, the number of PDX-1 immunopositive cells per islet area.
|
|
). These results suggest that the reduced expression of PDX-1 protein in LP rats was because of alterations in the translational process.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). As previously reported, low maternal glycemia caused by malnutrition accounted for the reduced liver glycogen concentration and consequent low serum glucose levels of the offspring (30
). The reduced body weight of LP rats may also have been related to the reduced serum insulin levels. Insulin exerts a profound effect on the growth of organs and on fetal metabolism, as judged by the hyperinsulinemia and macrosomia of neonates from noncompensated diabetic mothers (31
). In weaned LP rats, the postprandial serum glucose levels were lower than in C and R rats. These results were consistent with an increased sensitivity to insulin in the target tissues of these animals (32
). In R rats, all features were normalized, except for the body and pancreas weights which were still higher than in C rats. These findings confirmed and extended previous observations that no obvious alterations persisted at weaning when the protein deficiency was restricted to fetal life (33
–35
).
Protein deficiency impairs insulin secretion (8
), and this was confirmed by our experiments with isolated islets. LP islets showed reduced glucose-induced insulin secretion in the presence of a high concentration of glucose (16.7 mmol/L) compared with the C and R groups. It is conceivable that different steps in the mechanism of insulin secretion may be altered, such as a reduction in Ca2+ uptake by the islets (36
).
A reduction in islet size, a decrease in B-cell proliferation and a reduction in the size of the islet vascular bed have been related to protein restriction during pregnancy (10
). At birth, pups from LP dams had a much lower pancreas weight and islet size compared with the controls. After weaning (28 d old), these alterations were still present in LP rats, but the islet size was fully normalized in R rats, showing that the endocrine pancreas has considerable plasticity and is able to adapt to environmental changes during development, but only when the protein deficiency is restricted to fetal life (35
). Thus, independent of the increased sensitivity to insulin in target tissues, the reduced insulin secretion in islets from LP pups may result from intrinsic alterations in islets such as a smaller size and/or a reduced volume of B cells (37
).
One explanation for the reduced size of islets in LP rats could be the decrease in serum glucose, which could signal to the B cells that less insulin is required, so that the latter would not have to replicate or increase in size (38
). In addition, amino acids, particularly branched-chain amino acids, may promote B-cell proliferation by stimulating the phosphorylation of PHAS-1 (a regulator of translation initiation during mitogenesis) and by facilitating the proliferative effects mediated by growth factors (39
). Because branched-chain amino acids are most depleted in the plasma of fetuses from LP dams (40
), this could explain the lower rate of B-cell proliferation in the pancreas of LP pups. A reduced expression of insulin growth factor II may also contribute to the lower B-cell proliferation rate and increased apoptosis observed in the fetus and neonate after exposure to a LP diet (41
).
Alterations such as a reduced insulin secretion and a smaller size or reduced cell volume for B cells may also result from a decrease in insulin synthesis (10
). PDX-1 is an important B cell–specific transcription factor (42
) that links glucose metabolism to the regulation of insulin gene transcription (43
). Glucose activates PDX-1 through an insulin-dependent cell signaling pathway involving phosphatidylinositol 3-kinase. The stimulation of this pathway leads to phosphorylation and the activation of a cytoplasmic form of PDX-1 that translocates to the nucleus (26
). Thus, lower levels of circulating glucose in LP rats could contribute to the reduced PDX-1 expression.
The exposure of isolated islets to high concentrations of palmitic acid reduced PDX-1 mRNA and protein expression as well as PDX-1 binding activity for its cis regulatory elements in the insulin and GLUT-2 genes (22
). However, in islets from LP and C rats, PDX-1 mRNA levels were similar, indicating that the change in FFA levels in vivo can not account for the altered PDX-1 mRNA expression. The reduced PDX-1 protein expression in islets from LP rats was probably related to alterations in the translation process, as recently proposed (44
).
Taken together, these results indicate that a low protein diet during the fetal and lactation periods leads to alterations in islet size and functionality. These effects are linked to a reduction in PDX-1 protein, but not PDX-1 mRNA expression. The reintroduction of a normal diet immediately after birth normalizes the expression of PDX-1 protein and restores the islets cell mass and B-cell secretory capacity.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
3 Abbreviations used: C, control; FFA, free fatty acid; GLUT-2, glucose transporter isoform 2; LP, low protein; PCR, polymerase chain reaction; PDX-1, pancreatic duodenal homeobox 1; PPI, preproinsulin; R, recovered; TTBS, Tris Tween-20 buffered saline.
Manuscript received 19 April 2002. Initial review completed 30 May 2002. Revision accepted 19 July 2002.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
1. Lucas, A. (1990) Does early diet program future outcome?. Acta Pediatr. Scand. Suppl. 365:58-67.
2. Barker, D.J.P. & Clark, P. M. (1997) Fetal undernutrition and disease in later life. Rev. Reprod. 2:105-112.[Abstract]
3. Dennison, E., Fall, C., Cooper, C. & Barker, D. (1997) Prenatal factors influencing long-term outcome. Horm. Res. 48(Suppl.):25-29.
4. Behar, M. (1977) Protein-calorie deficits in developing countries. Ann. N. Y. Acad. Sci. 300:176-187.[Abstract]
5. Rao, R. H. (1988) Diabetes in the undernourished: coincidence or consequence. Endocr. Rev. 9:67-87.[Medline]
6. Hales, C. N., Barker, D.J.P., Clark, P.M.S., Cox, L. J., Fall, C., Osmond, C. & Winter, P. D. (1991) Fetal and infant growth and impaired glucose tolerance at age 64. Br. Med. J. 303:1019-1022.
7. Latorraca, M. Q., Carneiro, E. M., Boschero, A. C. & Mello, M.A.R. (1998) Protein deficiency during pregnancy and lactation impairs glucose-induced insulin secretion but increases the sensitivity to insulin in weaned rats. Br. J. Nutr. 80:291-297.[Medline]
8. Cherif, H., Reusens, B., Dahri, S. & Remacle, C. (2001) A protein-restricted diet during pregnancy alters in vitro insulin secretion from islets of fetal Wistar rats. J. Nutr. 131:1555-1559.
9. Blásquez, E., Motoya, E. & López Quijada, C. (1970) Relationship between insulin concentration in plasma and pancreas of fetal and weaning rats. J. Endocrinol. 48:453-461.
10. Snoeck, A., Remacle, C., Reusens, B. & Hoet, J. J. (1990) Effect of a low protein diet during pregnancy on the fetal rat endocrine pancreas. Biol. Neonate 57:107-118.[Medline]
11. Nielsen, D. A., Welsh, M., Casadaban, M. J. & Steiner, D. F. (1985) Control of insulin gene expression in pancreatic ß-cells and in an insulin-producing cell line, RIN-5F cells. Effects of glucose and cyclic AMP on the transcription of insulin mRNA. J. Biol. Chem. 260:13585-13589.
12. Permutt, M. A. & Kipnis, D. M. (1972) Insulin biosynthesis. I. On the mechanism of glucose stimulation. J. Biol. Chem. 247:1194-1199.
13. Efrat, S., Surana, M. & Fleischer, N. (1991) Glucose induces insulin gene transcription in a murine pancreatic ß-cell line. J. Biol. Chem. 266:11141-11143.
14. Leibiger, I. B., Leibiger, B., Moede, T. & Berggren, P. O. (1998) Exocytosis of insulin promotes insulin gene transcription via the insulin receptor/PI-3 kinase/p70s6 kinase and CaM kinase pathways. Mol. Cell. 1:933-938.[Medline]
15. Ashcroft, S. J., Bunce, J., Lowry, M., Hansen, S. E. & Hedeskov, C. J. (1978) The effect of sugars on (pro)insulin biosynthesis. Biochem. J. 174:517-526.[Medline]
16. Itoh, N. & Okamoto, H. (1980) Translational control of proinsulin synthesis by glucose. Nature (Lond.) 283:100-102.[Medline]
17. Welsh, M., Nielsen, D. A., MacKrell, A. J. & Steiner, D. F. (1985) Control of insulin gene expression in pancreatic beta-cells and in an insulin-producing cell line, RIN-5F cells. II. Regulation of insulin mRNA stability. J. Biol. Chem. 260:13590-13594.
18. Welsh, M., Brunstedt, J. & Hellerström, C. (1986) Effects of D-glucose, L-leucine, and 2-ketoisocaproate on insulin mRNA levels in mouse pancreatic islets. Diabetes 35:228-231.[Abstract]
19. German, M., Ashcroft, S., Docherty, K., Edlund, H., Edlund, T., Goodison, S., Imura, H., Kennedy, G., Madsen, O., Melloul, D., Moss, L., Olson, K., Permutt, A., Philippe, J., Robertson, R. P., Rutter, W. J., Serup, P., Stein, R., Steiner, D., Tsai, M.-J. & Walker, M. D. (1995) The insulin gene promoter: a simplified nomenclature. Diabetes 44:1002-1004.[Medline]
20. Ahlgren, U., Jonsson, J. & Edlund, H. (1996) The morphogenesis of the pancreatic mesenchyme is uncoupled from that of the pancreatic epithelium in IPF1/PDX1-deficient mice. Development 122:1409-1416.[Abstract]
21. Jonsson, J., Carlsson, L., Edlund, T. & Edlund, H. (1994) Insulin-promoter-factor 1 is required for pancreas development in mice. Nature (Lond.) 6498:606-609.
22. Gremlich, S., Bonny, C., Waeber, G. & Thorens, B. (1997) Fatty acids decrease IDX-1 expression in rat pancreatic islets and reduce GLUT2, glucokinase, insulin, and somatostatin levels. J. Biol. Chem. 272:30261-30269.
23. Melloul, D., Ben-Neriah, Y. & Cerasi, E. (1993) Glucose modulates the binding of an islet-specific factor to a conserved sequence within the rat I and the human insulin promoters. Proc. Natl. Acad. Sci. USA 90:3865-3869.
24. Macfarlane, W. M., Read, M. L., Gilligan, M., Bujalska, I. & Docherty, K. (1994) Glucose modulates the binding activity of the ß-cell transcription factor IUF1 in a phosphorylation-dependent manner. Biochem. J. 303:625-631.
25. Marshak, S., Totary, H., Cerasi, E. & Melloul, D. (1996) Purification of the ß-cell glucose-sensitive factor that transactivates the insulin gene differentially in normal and transformed islet cells. Proc. Natl. Acad. Sci. USA 93:15057-15062.
26. Macfarlane, W. M., McKinnon, C. M., Felton-Edkins, Z. A., Cragg, H., James, R. F. & Docherty, K. (1999) Glucose stimulates translocation of the homeodomain transcription factor PDX1 from the cytoplasm to the nucleus in pancreatic beta-cells. J. Biol. Chem. 274:1011-1016.
27. Reis, M. A., Carneiro, E. M., Mello, M. A., Boschero, A. C., Saad, M. J. & Velloso, L. A. (1997) Glucose-induced insulin secretion is impaired and insulin-induced phosphorylation of the insulin receptor and insulin receptor substrate-1 are increased in protein-deficient rats. J. Nutr. 127:403-410.
28. Scott, A. M., Atwater, I. & Rojas, E. (1981) A method for the simultaneous measurement of insulin release and B-cell membrane potential in single mouse islets of Langerhans. Diabetologia. 21:470-475.[Medline]
29. Sokal, R. R. & Rohlf, F. J. (1981) The Principles and Practice of Statistics in Biological Research 1981:400-453 W.H. Freeman and Co. New York, NY. .
30. Mello, M.A.R., Cury, L., Valle, L.B.S. & Oliveira-Filho, R. M. (1987) Pregnancy in young rats: effects of malnutrition. Nutr. Rep. Intern. 36:527-535.
31. Van Assche, F. A. & Aerts, L. (1979) The fetal endocrine pancreas. Contrib. Gynecol. Obstet. 5:444-457.
32. Latorraca, M. Q., Reis, M.A.B., Carneiro, E. M., Mello, M.A.R., Velloso, L. A., Saad, M.J.A. & Boschero, A. C. (1998) Protein deficiency and nutritional recovery modulate insulin secretion and the early steps of insulin action in rats. J. Nutr. 128:1643-1649.
33. Dahri, S., Snoeck, A., Reusens-Billen, B., Remacle, C. & Hoet, J. J. (1991) Islet function in offspring of mothers on low protein diet during gestation. Diabetes 40(Suppl.):115-120.
34. Dahri, S., Reusens, B., Remacle, C. & Hoet, J. J. (1995) Nutritional influences on pancreatic development and potential links with non-insulin-dependent diabetes. Proc. Nutr. Soc. 54:345-356.[Medline]
35. Rasschaert, J., Reusens, B., Dahri, S., Sener, A., Remacle, C., Hoet, J. J. & Malaisse, W. J. (1995) Impaired activity of rat pancreatic islet mitochondrial glycerophosphate dehydrogenase in protein malnutrition. Endocrinology 136:2631-2634.[Abstract]
36. Carneiro, E. M., Mello, M.A.R., Gobatto, C. A. & Boschero, A. C. (1995) Low protein diet impairs glucose-induced insulin secretion from and 45Ca uptake by pancreatic rat islets. J. Nutr. Biochem. 6:314-318.
37. Rao, R. H. (1990) Chronic undernutrition may accentuate the ß cell dysfunction of type 2 diabetes. Diabetes Res. Clin. Pract. 8:125-130.[Medline]
38. Bonner-Weir, S. (2000) Perspective: postnatal pancreatic beta cell growth. Endocrinology 141:1926-1929.
39. Xu, G., Kwon, G., Marshall, C. A., Lin, T. A., Lawrence, J. C., Jr & McDaniel, M. L. (1998) Branched-chain amino acids are essential in the regulation of PHAS-I and p70 S6 kinase by pancreatic ß-cells. A possible role in protein translation and mitogenic signaling. J. Biol. Chem. 273:28178-28184.
40. Reusens, B., Dahri, S., Snoeck, A., Bennis-Taleb, N., Remacle, C. & Hoet, J. J. (1995) Long term consequences of diabetes and its complications may have a fetal origin: experimental and epidemiological evidence. Cowett, R. M. eds. Diabetes 35:187-198 Nestlé Nutrition Workshop Series Raven Press, New York, NY. .
41. Petrik, J., Reusens, B., Arany, E., Remacle, C., Coelho, C., Hoet, J. J. & Hil, D. J. (1999) A low protein diet alters the balance of islet cell replication and apoptosis in the fetal and neonatal rat and is associated with a reduced pancreatic expression of insulin-like growth factor-II. Endocrinology 140:4861-4873.
42. Ohlsson, H., Karlsson, K. & Edlund, T. (1993) IPF1, a homeodomain-containing transactivator of the insulin gene. EMBO J. 12:4251-4259.[Medline]
43. Wu, H., Macfarlane, W. M., Tadayyon, M., Arch, J.R.S., James, R.F.L. & Docherty, K. (1999) Insulin stimulates pancreatic-duodenal homeobox factor-1 (PDX1) DNA-binding activity and insulin promoter activity in pancreatic B-cell. Biochem. J. 344:813-818.
44. Fafournoux, P., Bruhat, A. & Jousse, C. (2000) Amino acid regulation of gene expression. Biochem. J. 351:1-12.[Medline]
This article has been cited by other articles:
|
|
 |
|
  X. Wang, L. Liang, and L. Du The effects of intrauterine undernutrition on pancreas ghrelin and insulin expression in neonate rats J. Endocrinol., July 1, 2007; 194(1): 121 - 129. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. E. Cerf, K. Williams, X. I. Nkomo, C. J. Muller, D. F. Du Toit, J. Louw, and S. A. Wolfe-Coote Islet cell response in the neonatal rat after exposure to a high-fat diet during pregnancy Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2005; 288(5): R1122 - R1128. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. A. Martin, E. Fernandez, A. M. Pascual-Leone, F. Escriva, and C. Alvarez Protein calorie restriction has opposite effects on glucose metabolism and insulin gene expression in fetal and adult rat endocrine pancreas Am J Physiol Endocrinol Metab, April 1, 2004; 286(4): E542 - E550. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
