Lactating SKH-1 furless mice prioritize own comfort over growth of their pups.

Lactation is the most energetically demanding physiological process that occurs in mammalian females, and as a consequence of this energy expenditure, lactating females produce an enormous amount of excess heat. This heat is thought to limit the amount of milk a mother produces, and by improving heat dissipation, females may improve their milk production and offspring quality. Here we used SKH-1 hairless mice as a natural model of improved heat dissipation. Lactating mothers were given access to a secondary cage to rest away from their pups, and this secondary cage was kept either at room temperature (22 °C) in the control rounds or cooled to 8 °C in the experimental groups. We hypothesized that the cold exposure would maximize the heat dissipation potential, leading to increased milk production and healthier pups even in the hairless mouse model. However, we found the opposite, where cold exposure allowed mothers to eat more food, but they produced smaller weight pups at the end of lactation. Our results suggest that mothers prioritize their own fitness, even if it lowers the fitness of their offspring in this particular mouse strain. This maternal-offspring trade-off is interesting and requires future studies to understand the full interaction of maternal effects and offspring fitness in the light of the heat dissipation limitation.

Tracking Ca2+ Dynamics in NOD Mouse Islets During Spontaneous Diabetes Development.

The mechanisms accounting for the functional changes of α- and ß-cells over the course of type 1 diabetes (T1D) development are largely unknown. Permitted by our established technology of high spatiotemporal resolution imaging of cytosolic Ca2+ ([Ca2+]c) dynamics on fresh pancreas tissue slices, we tracked the [Ca2+]c dynamic changes, as the assessment of function, in islet α- and ß-cells of female nonobese diabetic (NOD) mice during the development of spontaneous diabetes. We showed that, during the phases of islet inflammation, 8 mmol/L glucose-induced synchronized short [Ca2+]c events in ß-cells were diminished, whereas long [Ca2+]c events were gradually more triggerable at substimulatory 4 and 6 mmol/L glucose. In the islet destruction phase, the synchronized short [Ca2+]c events in a subset of ß-cells resumed at high glucose condition, while the long [Ca2+]c events were significantly elevated already at substimulatory glucose concentrations. In the α-cells, the glucose sensitivity of the [Ca2+]c events persisted throughout the course of T1D development. At the late islet destruction phase, the α-cell [Ca2+]c events exhibited patterns of synchronicity. Our work has uncovered windows of functional recovery in ß-cells and potential α-cells functional synchronization in NOD mice over the course of T1D development. ARTICLE HIGHLIGHTS: In NOD mice ß-cells, 8 mmol/L glucose-induced synchronized short [Ca2+]c events diminish in the early phases of islet inflammation, and long Ca2+ events became more sensitive to substimulatory 4 and 6 mmol/L glucose. In the late islet destruction phase, the synchronized short [Ca2+]c events in a subset of ß-cells resumed at 8 mmol/L glucose, while the long Ca2+ events were significantly elevated at substimulatory glucose concentrations. In the α-cells, the glucose sensitivity of the [Ca2+]c events persisted throughout the course of type 1 diabetes development. α-Cell [Ca2+]c events occasionally synchronize in the islets with severe ß-cell destruction.

High-resolution analysis of the cytosolic Ca2+ events in ß cell collectives in situ.

The release of peptide hormones is predominantly regulated by a transient increase in cytosolic Ca2+ concentration ([Ca2+]c). To trigger exocytosis, Ca2+ ions enter the cytosol from intracellular Ca2+ stores or from the extracellular space. The molecular events of late stages of exocytosis, and their dependence on [Ca2+]c, were extensively described in isolated single cells from various endocrine glands. Notably, less work has been done on endocrine cells in situ to address the heterogeneity of [Ca2+]c events contributing to a collective functional response of a gland. For this, ß cell collectives in a pancreatic islet are particularly well suited as they are the smallest, experimentally manageable functional unit, where [Ca2+]c dynamics can be simultaneously assessed on both cellular and collective level. Here, we measured [Ca2+]c transients across all relevant timescales, from a subsecond to a minute time range, using high-resolution imaging with a low-affinity Ca2+ sensor. We quantified the recordings with a novel computational framework for automatic image segmentation and [Ca2+]c event identification. Our results demonstrate that under physiological conditions the duration of [Ca2+]c events is variable, and segregated into three reproducible modes, subsecond, second, and tens of seconds time range, and are a result of a progressive temporal summation of the shortest events. Using pharmacological tools we show that activation of intracellular Ca2+ receptors is both sufficient and necessary for glucose-dependent [Ca2+]c oscillations in ß cell collectives, and that a subset of [Ca2+]c events could be triggered even in the absence of Ca2+ influx across the plasma membrane. In aggregate, our experimental and analytical platform was able to readily address the involvement of intracellular Ca2+ receptors in shaping the heterogeneity of [Ca2+]c responses in collectives of endocrine cells in situ.NEW & NOTEWORTHY Physiological glucose or ryanodine stimulation of ß cell collectives generates a large number of [Ca2+]c events, which can be rapidly assessed with our newly developed automatic image segmentation and [Ca2+]c event identification pipeline. The event durations segregate into three reproducible modes produced by a progressive temporal summation. Using pharmacological tools, we show that activation of ryanodine intracellular Ca2+ receptors is both sufficient and necessary for glucose-dependent [Ca2+]c oscillations in ß cell collectives.

Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levels.

Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.

pH-Dependence of Glucose-Dependent Activity of Beta Cell Networks in Acute Mouse Pancreatic Tissue Slice.

Extracellular pH has the potential to affect various aspects of the pancreatic beta cell function. To explain this effect, a number of mechanisms was proposed involving both extracellular and intracellular targets and pathways. Here, we focus on reassessing the influence of extracellular pH on glucose-dependent beta cell activation and collective activity in physiological conditions. To this end we employed mouse pancreatic tissue slices to perform high-temporally resolved functional imaging of cytosolic Ca2+ oscillations. We investigated the effect of either physiological H+ excess or depletion on the activation properties as well as on the collective activity of beta cell in an islet. Our results indicate that lowered pH invokes activation of a subset of beta cells in substimulatory glucose concentrations, enhances the average activity of beta cells, and alters the beta cell network properties in an islet. The enhanced average activity of beta cells was determined indirectly utilizing cytosolic Ca2+ imaging, while direct measuring of insulin secretion confirmed that this enhanced activity is accompanied by a higher insulin release. Furthermore, reduced functional connectivity and higher functional segregation at lower pH, both signs of a reduced intercellular communication, do not necessary result in an impaired insulin release.