vH+-ATPase-induced intracellular acidification is critical to glucose-stimulated insulin secretion in beta cells.

Swelling of secretory vesicles is critical for the regulated release of intra-vesicular contents from cells during secretion. At the secretory vesicle membrane of the exocrine pancreas and neurons, GTP-binding G proteins, vH+-ATPase, potassium channels and AQP water channels, are among the players implicated in vesicle volume regulation. Here we report in the endocrine insulin-secreting MIN6 cells, the similar requirement of vH+-ATPase-mediated intracellular acidification on glucose-stimulated insulin release. MIN6 cells exposed to the vH+-ATPase inhibitor Bafilomycin A show decreased acidification of the cytosolic compartment that include insulin-carrying granules. Additionally, a loss of insulin granules near the cell plasma membrane following Bafilomycin A treatment, suggests impaired transport of insulin granules and consequent decrease in glucose-stimulated insulin secretion and accumulation of intracellular insulin. These results suggest that vH+-ATPase-mediated intracellular acidification is required for insulin secretion in beta cells.

Nanoscale imaging using differential expansion microscopy.

Expensive and time-consuming approaches of immunoelectron microscopy of biopsy tissues continues to serve as the gold-standard for diagnostic pathology. The recent development of the new approach of expansion microscopy (ExM) capable of fourfold lateral expansion of biological specimens for their morphological examination at approximately 70 nm lateral resolution using ordinary diffraction limited optical microscopy, is a major advancement in cellular imaging. Here we report (1) an optimized fixation protocol for retention of cellular morphology while obtaining optimal expansion, (2) an ExM procedure for up to eightfold lateral and over 500-fold volumetric expansion, (3) demonstrate that ExM is anisotropic or differential between tissues, cellular organelles and domains within organelles themselves, and (4) apply image analysis and machine learning (ML) approaches to precisely assess differentially expanded cellular structures. We refer to this enhanced ExM approach combined with ML as differential expansion microscopy (DiExM), applicable to profiling biological specimens at the nanometer scale. DiExM holds great promise for the precise, rapid and inexpensive diagnosis of disease from pathological specimen slides.