Intravital imaging of islet Ca2+ dynamics reveals enhanced β cell connectivity after bariatric surgery in mice

Bariatric surgery improves both insulin sensitivity and secretion and can induce diabetes remission. However, the mechanisms and time courses of these changes, particularly the impact on β cell function, are difficult to monitor directly. In this study, we investigated the effect of Vertical Sleeve Gastrectomy (VSG) on β cell function in vivo by imaging Ca2+ dynamics in islets engrafted into the anterior eye chamber. Mirroring its clinical utility, VSG in mice results in significantly improved glucose tolerance, and enhanced insulin secretion. We reveal that these benefits are underpinned by augmented β cell function and coordinated activity across the islet. These effects involve changes in circulating GLP-1 levels which may act both directly and indirectly on the β cell, in the latter case through changes in body weight. Thus, bariatric surgery leads to time-dependent increases in β cell function and intra-islet connectivity which are likely to contribute to diabetes remission.


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Research sample Sampling strategy Statement included in the manuscript. No large datasets were generated and all relevant data are included in the manuscript itself or in the supplemental information. all data supporting the findings of this study are available within the paper and its supplementary information files. The custom made script that supports the connectivity findings of this study are available in GitHub with the identifier 'Connectivity-calcium/ Pearson-correlation-coefficient-analysis'.
For imaging experiments, power calculations were performed based on previous islet-in-ACE experiments or in vitro calcium dynamic experiments (e.g. Salem V., et al, Nat Metab, 2019). Five individual islets and >50 individual rois provided enough evidence of a change in calcium readout between a low and high glucose state and between other conditions e.g. surgery or incretin treatment. Sample size was determined to be adequate based on the magnitude and consistency of measurable differences between groups. Sample sizes for measurements of metabolic parameters (body weight, IPGTT, OGTT etc) were based on previous results (eg Amouyal C. et al EBioMedicine, 2020).
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Experiments were performed on multiple animals as per the power calculations above and the number of replicate experiments is stated in the manscript. Specifically, after an initial pilot experiment (data not included) the central observations around the impact of VSG on calcium dynamics in the islet were performed on two entirely separate cohorts of mice, each involving at least n=4 animals per condition.
The animals were randomised in either sham or VSG group according to their body weight and fasted glycemia, to ensure equal average body weight and diabetes status per group.
In order to reduce the potential confounder of bleaching or duration of exposure to anaesthetic, the low vs high recordings were taken in random order (as per Salem, V et al Nat Metab, 2019).
Operators were blinded as to group for imaging experiments. Blinding was not possible for the metabolic measurements. Thus, Dr Akalestou performed all surgeries and metabolic studies and she was therefore aware of the cage to group allocation as it was crucial for appropriate peri-operative care.
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