The effects of maternal protein deprivation on the fetal rat pancreas: major structural changes and their recuperation

Early protein restriction increases intra-islet GLP-1 production and pancreatic β-cell proliferation mediated by the β-catenin pathway

PURPOSE

In the present study, we investigated whether intra-islet GLP-1 production and its modulation have a role in apoptosis, proliferation or neogenesis that is compromised by protein restriction during the foetal and suckling periods.

METHODS

Exendin-4, a GLP-1 receptor agonist (treated groups), or saline (non-treated groups) was intraperitoneally administered for 15 days from 75 to 90 days of age in female adult rats consisting of offspring born to and suckled by mothers fed a control diet (control groups) and who had the same diet until 90 days of age or offspring born to and suckled by mothers fed a low-protein diet and who were fed the control diet after weaning until 90 days of age (protein-restricted group).

RESULTS

The β-cell mass was lower in the protein-restricted groups than in the control groups. Exendin-4 increased β-cell mass, regardless of the mother's protein intake. The colocalization of GLP-1/glucagon was higher in the protein-restricted rats than in control rats in both the exendin-4-treated and non-treated groups. The frequency of cleaved caspase-3-labelled cells was higher in the non-treated protein-restricted group than in the non-treated control group and was similar in the treated protein-restricted and treated control groups. Regardless of treatment with exendin-4, Ki67-labelled cell frequency and β-catenin/DAPI colocalization were elevated in the protein-restricted groups. Exendin-4 increased the area of endocrine cell clusters and β-catenin/DAPI and FoxO1/DAPI colocalization regardless of the mother's protein intake.

CONCLUSIONS

Protein restriction in early life increased intra-islet GLP-1 production and β-cell proliferation, possibly mediated by the β-catenin pathway.

Noninvasive in vivo imaging of embryonic β-cell development in the anterior chamber of the eye

The fetal environment plays a decisive role in modifying the risk for developing diabetes later in life. Developing novel methodology for noninvasive imaging of β-cell development in vivo under the controlled physiological conditions of the host can serve to understand how this environment affects β-cell growth and differentiation. A number of culture models have been designed for pancreatic rudiment but none match the complexity of the in utero or even normal physiological environment. Speier et al. recently developed a platform of noninvasive in vivo imaging of pancreatic islets using the anterior chamber of the eye where islets get vascularized, grow and respond to physiological changes. The same methodology was adapted for the study of pancreatic development. E13.0, still undifferentiated rudiments with fluorescent lineage tracing were implanted in the AC of the eye, allowing the longitudinal study of their growth and differentiation. Within 48 h the anlages get vascularized and grow but their mesenchyme displays a selective growth advantage. The resulting imbalance leads to alteration in the differentiation pattern of the progenitors. Reducing the mesenchyme to its bare minimum before implantation allows the restoration of a proper balance and a development that mimics the normal pancreatic development. These groundbreaking observations demonstrate that the anterior chamber of the eye provides a good system for noninvasive in vivo fluorescence imaging of the developing pancreas under the physiology of the host and can have important implications for designing strategies to prevent or reverse the deleterious effects of hyperglycemia on altering β-cell function later in life.