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Aims/hypothesis: Tissue-resident macrophages sense the microenvironment and respond by producing signals that act locally to maintain a stable tissue state. It is now known that pancreatic islets contain their own unique resident macrophages, which have been shown to promote proliferation of the insulin-secreting beta cell. However, it is unclear how beta cells communicate with islet-resident macrophages. Here we hypothesised that islet macrophages sense changes in islet activity by detecting signals derived from beta cells. Methods: To investigate how islet-resident macrophages respond to cues from the microenvironment, we generated mice expressing a genetically encoded Ca 2+ indicator in myeloid cells. We produced living pancreatic slices from these mice and used them to monitor macrophage responses to stimulation of acinar, neural and endocrine cells. Results: Islet-resident macrophages expressed functional purinergic receptors, making them exquisite sensors of interstitial ATP levels. Indeed, islet-resident macrophages responded selectively to ATP released locally from beta cells that were physiologically activated with high levels of glucose. Because ATP is co-released with insulin and is exclusively secreted by beta cells, the activation of purinergic receptors on resident macrophages facilitates their awareness of beta cell secretory activity. Conclusions/interpretation: Our results indicate that islet macrophages detect ATP as a proxy signal for the activation state of beta cells. Sensing beta cell activity may allow macrophages to adjust the secretion of factors to promote a stable islet composition and size.

slet cell hormone release is modulated by signals from endothelial and endocrine cells within the islet. However, models of intra-islet vascularization and paracrine cell signaling are mostly based on rodent pancreas. We here assessed for the first time the architecture and endocrine cell interaction of the vascular network in unperturbed human islets in situ and their potential to re-establish their endogenous vascular network after transplantation in vivo. We prepared pancreas tissue slices of fresh tissue obtained from non-diabetic patients undergoing partial pancreatectomy. In addition, we transplanted human donor islets into the anterior chamber of the mouse eye. Next, we performed three-dimensional in situ and in vivo imaging of islet cell and vessel architecture at cellular resolution and compared our findings to mouse and porcine islets. Our data reveal a significantly different vascular architecture with decreased vessel diameter, reduced vessel branching and shortened total vessel network in human compared to mouse islets. Together with the distinct cellular arrangement in human islets this limits beta-endothelial cell interactions, facilitates connection of alpha and beta cells and promotes the formation of independent beta cell clusters within islets. Furthermore, our results show that the endogenous vascular network of islets is significantly altered after transplantation in a donor-age related mechanism. Thus, our study provides new insight into vascular architecture and cellular arrangement of human islets with apparent consequences for intercellular islet signaling. Moreover, our findings suggest that human islet engraftment after transplantation can be improved by the use of alternative, less mature islet cell sources.

Emerging insulin resistance is normally compensated by increased insulin production of pancreatic β-cells, thereby maintaining normoglycemia. However, it is unclear whether this is achieved by adaption of β-cell function, mass, or both. Most importantly it is still unknown which of these adaptive mechanisms fail when type 2 diabetes develops. We performed longitudinal in vivo imaging of β-cell calcium dynamics and islet mass of transplanted islets of Langerhans throughout diet-induced progression from normal glucose homeostasis, over compensation of insulin resistance to pre-diabetes. The results show that compensation of insulin resistance is predominated by alterations of β-cell function, while islet mass only gradually expands. Hereby, functional adaptation is mediated by increased calcium efficacy, which involves Epac signaling. Prior to prediabetes, β-cell function displays decreased stimulated calcium dynamics, whereas islet mass continues to increase through prediabetes onset. Thus, our data reveal a predominant role of islet function with distinct contributions of triggering and amplifying pathway in the in vivo processes preceding diabetes onset. These findings support protection and recovery of β-cell function as primary goal for prevention and treatment of diabetes and provide insight into potential therapeutic targets.

Studies on the cellular function of the pancreas are typically performed in vitro on its isolated functional units, the endocrine islets of Langerhans and the exocrine acini. However, these approaches are hampered by preparation-induced changes of cell physiology and the lack of an intact surrounding. We present here a detailed protocol for the preparation of pancreas tissue slices. This procedure is less damaging to the tissue and faster than alternative approaches, and it enables the in situ study of pancreatic endocrine and exocrine cell physiology in a conserved environment. Pancreas tissue slices facilitate the investigation of cellular mechanisms underlying the function, pathology and interaction of the endocrine and exocrine components of the pancreas. We provide examples for several experimental applications of pancreas tissue slices to study various aspects of pancreas cell biology. Furthermore, we describe the preparation of human and porcine pancreas tissue slices for the validation and translation of research findings obtained in the mouse model. Preparation of pancreas tissue slices according to the protocol described here takes less than 45 min from tissue preparation to receipt of the first slices.

Inorganic arsenic is a well-documented, exposure relevant human carcinogen. A promising starting point to further understand the mechanisms behind inorganic arsenic carcinogenicity might be a formation of reactive, highly toxic metabolites during human arsenic metabolism. This study characterises the toxicity of recently identified S-containing arsenic metabolites in cultured human A549 lung adenocarcinoma epithelium cells. In direct comparison to arsenite, thio-dimethylarsinic acid (thio-DMA(V)) and dimethylarsinic glutathione (DMAG) exerted a 5- to 20-fold stronger cytotoxicity and showed a 2- to 20-fold higher cellular bioavailability, respectively. All three arsenicals disturbed cell cycle progression at cytotoxic concentrations, but failed to increase the level of reactive oxygen and nitrogen species (RONS) in healthy A549 cells. However, a strong disturbance of the oxidative defense system was observed after incubation with absolutely sub-cytotoxic, pico- to nanomolar concentrations of arsenite and thio-DMA(V), respectively. Thus, both GSH and GSSG levels were significantly decreased by up to 40%. Accordingly, RONS levels of oxidatively (H2O2) stressed cells were strongly increased by the arsenicals. Since in vivo RONS are permanently endogenously and exogenously produced, this boost of the existing oxidative stress by arsenite and thio-DMA(V) might contribute to the process of inorganic arsenic induced carcinogenicity.

Aims/hypothesis Pancreatic beta cells maintain glucose homeostasis and beta cell dysfunction is a major risk factor in developing diabetes. Therefore, understanding the developmental regulatory networks that define a fully functional beta cell is important for elucidating the genetic origins of the disease. Aldehyde dehydrogenase activity has been associated with stem/progenitor cells and we have previously shown that Aldh1b1 is specifically expressed in pancreas progenitor pools. Here we address the hypothesis that Aldh1b1 may regulate the timing of the appearance and eventual functionality of beta cells. Methods We generated an Aldh1b1-knockout mouse line (Aldh1b1tm1lacZ) and used this to study pancreatic development, beta cell functionality and glucose homeostasis in the absence of Aldh1b1 function. Results Differentiation in the developing pancreas of Aldh1b1tm1lacZ null mice was accelerated. Transcriptome analyses of newborn and adult islets showed misregulation of key beta cell transcription factors and genes crucial for beta cell function. Functional analyses showed that glucose-stimulated insulin secretion was severely compromised in islets isolated from null mice. Several key features of beta cell functionality were affected, including control of oxidative stress, glucose sensing, stimulus-coupling secretion and secretory granule biogenesis. As a result of beta cell dysfunction, homozygous mice developed glucose intolerance and age-dependent hyperglycaemia. Conclusions/interpretation These findings show that Aldh1b1 influences the timing of the transition from the pancreas endocrine progenitor to the committed beta cell and demonstrate that changes in the timing of this transition lead to beta cell dysfunction and thus constitute a diabetes risk factor later in life. Gene Expression Omnibus (GEO) accession: GSE58025 Electronic supplementary material The online version of this article (doi:10.1007/s00125-015-3784-4) contains peer-reviewed but unedited supplementary material, which is available to authorised users.