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. 2015 Jan 16;48(1):3.
doi: 10.1186/0717-6287-48-3.

A low-protein diet during pregnancy prevents modifications in intercellular communication proteins in rat islets

Ana Flávia Marçal-Pessoa  1 , Carmen Lucia Bassi-Branco  2 , Cristiana Dos Santos Barbosa Salvatierra  3 , Luiz Fabrizio Stoppiglia  4 , Letícia Martins Ignacio-Souza  5 , Sílvia Regina de Lima Reis  6 , Roberto Vilela Veloso  7 , Marise Auxiliadora de Barros Reis  8 , Everardo Magalhães Carneiro  9 , Antonio Carlos Boschero  10 , Vanessa Cristina Arantes  11 , Márcia Queiroz Latorraca  12
Affiliations

A low-protein diet during pregnancy prevents modifications in intercellular communication proteins in rat islets

Ana Flávia Marçal-Pessoa et al. Biol Res. .

Abstract

Background: Gap junctions between β-cells participate in the precise regulation of insulin secretion. Adherens junctions and their associated proteins are required for the formation, function and structural maintenance of gap junctions. Increases in the number of the gap junctions between β-cells and enhanced glucose-stimulated insulin secretion are observed during pregnancy. In contrast, protein restriction produces structural and functional alterations that result in poor insulin secretion in response to glucose. We investigated whether protein restriction during pregnancy affects the expression of mRNA and proteins involved in gap and adherens junctions in pancreatic islets. An isoenergetic low-protein diet (6% protein) was fed to non-pregnant or pregnant rats from day 1-15 of pregnancy, and rats fed an isocaloric normal-protein diet (17% protein) were used as controls.

Results: The low-protein diet reduced the levels of connexin 36 and β-catenin protein in pancreatic islets. In rats fed the control diet, pregnancy increased the levels of phospho-[Ser(279/282)]-connexin 43, and it decreased the levels of connexin 36, β-catenin and beta-actin mRNA as well as the levels of connexin 36 and β-catenin protein in islets. The low-protein diet during pregnancy did not alter these mRNA and protein levels, but avoided the increase of levels of phospho-[Ser(279/282)]-connexin 43 in islets. Insulin secretion in response to 8.3 mmol/L glucose was higher in pregnant rats than in non-pregnant rats, independently of the nutritional status.

Conclusion: Short-term protein restriction during pregnancy prevented the Cx43 phosphorylation, but this event did not interfer in the insulin secretion.

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Figures

Figure 1
Figure 1
Glucose stimulation of insulin secretion by islets from non-pregnant controls (CN), pregnant controls (CP), low-protein non-pregnant rats (LPNP) and low-protein pregnant rats (LPP). Groups of 5 islets were incubated for 90 min in Krebs-bicarbonate medium containing (A) 5.6 or (B) 8.3 mmol/L glucose. The columns represent the cumulative 90-min insulin secretion and are the means ± SD of 5–9 independent experiments. Columns with different superscript minuscule letters are significantly different by two-way ANOVA followed by a least significant difference (LSD) test (P < 0.05).
Figure 2
Figure 2
Cx36 mRNA and protein expression in islets from non-pregnant controls (CN), pregnant controls (CP), low-protein non-pregnant rats (LPNP) and low-protein pregnant rats (LPP). (A) and (B) Cx36 mRNA and protein expression in a heart sample (negative control), brain (positive control) and islets, respectively. (C) and (D) Cx36 mRNA and protein expression in islets from pregnant and non-pregnant rats fed control or low-protein diets. The Cx36 mRNA content was normalized to RPS29 mRNA. The columns represent the means ± SD of 3–5 independent experiments. Columns with different superscript minuscule letters are significantly different by two-way ANOVA followed by a least significant difference (LSD) test (P < 0.05).
Figure 3
Figure 3
Cx43 mRNA and protein expression in islets from non-pregnant controls (CN), pregnant controls (CP), low-protein non-pregnant rats (LPNP) and low-protein pregnant rats (LPP). (A) and (B) Cx43 mRNA and protein expression in a liver sample (negative control), heart (positive control) and islets, respectively. (C) and (D) Cx43 mRNA and protein expression in islets from pregnant and non-pregnant rats fed control or low-protein diets. The mRNA concentration of Cx43 is expressed relative to RPS29 mRNA. (E) Phospho-[Ser279/282]-Cx43 content in islets from pregnant and non-pregnant rats fed control or low-protein diets. The columns represent the means ± SD of 3–5 independent experiments. Columns with different superscript minuscule letters are significantly different by two-way ANOVA followed by a least significant difference (LSD) test (P < 0.05).
Figure 4
Figure 4
β-catenin mRNA and protein expression in islets from non-pregnant controls (CN), pregnant controls (CP), low-protein non-pregnant rats (LPNP) and low-protein pregnant rats (LPP). (A) and (B) β-catenin mRNA and protein expression in a heart sample (positive control) and islets. (C) and (D) β-catenin mRNA and protein expression in islets from pregnant and non-pregnant rats fed control or low-protein diets. The mRNA concentration of β-catenin is expressed relative to RPS29 mRNA. The columns represent the means ± SD of 3–6 independent experiments. Columns with different superscript minuscule letters are significantly different by two-way ANOVA followed by a least significant difference (LSD) test (P < 0.05).
Figure 5
Figure 5
β-actin mRNA expression in islets from non-pregnant controls (CN), pregnant controls (CP), low-protein non-pregnant rats (LPNP) and low-protein pregnant rats (LPP). The mRNA concentration of β-actin is expressed relative to RPS29 mRNA. The columns represent the means ± SD of 3–4 independent experiments. Columns with different superscript minuscule letters are significantly different by two-way ANOVA followed by a least significant difference (LSD) test (P < 0.05).
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