Evidence of a developmental origin for β-cell heterogeneity using a dual lineage-tracing technology

CRISPR/Cas9-mediated knockin of IRES-tdTomato at Ins2 locus reveals no RFP-positive cells in mouse islets

Using the CRISPR/Cas9 genomic editing technology, we constructed a transgenic mouse model to express specific fluorescent protein in pancreatic β cells, which harbor tdTomato exogenous gene downstream of the Ins2 promoter in C57BL/6 J mice. The Ins2-specific single-guide RNA-targeted exon2 was designed for the CRISPR/Cas9 system and Donor vector was constructed at the same time. Then Cas9, sgRNA, and Donor vector were microinjected in vitro into the mouse zygotes that were implanted into pseudo-pregnant mice. We obtained homozygotes through mating heterozygotes, and verified the knockin effect through genotype identification, in vivo imaging, and frozen section. Six F0 mice and stable inherited Ins2-IRES-tdTomato F1 were obtained. Genome sequencing results showed that the knockin group had no change in the Ins2 exon compared with the control group, while only the base sequence of tdTomato was added and no base mutation occurred. However, in vivo imaging and frozen section did not observe the expression of red fluorescent protein (RFP), and the protein expression of knockin gene tdTomato was negative. As a result, the expressions of tdTomato protein and fluorescence intensity were low and the detection threshold was not reached. In the CRISP/Cas9 technique, the exogenous fragment of IRES connection would affect the transcription level of the preceding gene, which in turn would lead to low-level expression of the downstream gene and affect the effect of gene insertion.

Sex-biased islet β cell dysfunction is caused by the MODY MAFA S64F variant by inducing premature aging and senescence in males

A heterozygous missense mutation of the islet β cell-enriched MAFA transcription factor (p.Ser64Phe [S64F]) is found in patients with adult-onset β cell dysfunction (diabetes or insulinomatosis), with men more prone to diabetes than women. This mutation engenders increased stability to the unstable MAFA protein. Here, we develop a S64F MafA mouse model to determine how β cell function is affected and find sex-dependent phenotypes. Heterozygous mutant males (MafAS64F/+) display impaired glucose tolerance, while females are slightly hypoglycemic with improved blood glucose clearance. Only MafAS64F/+ males show transiently higher MafA protein levels preceding glucose intolerance and sex-dependent changes to genes involved in Ca2+ signaling, DNA damage, aging, and senescence. MAFAS64F production in male human β cells also accelerate cellular senescence and increase senescence-associated secretory proteins compared to cells expressing MAFAWT. These results implicate a conserved mechanism of accelerated islet aging and senescence in promoting diabetes in MAFAS64F carriers in a sex-biased manner.

Probing β-Cell Biology in Space and Time

β-Cells in the islet of Langerhans have a central role in maintaining energy homeostasis. Understanding the physiology of β-cells and other islet cells requires a deep understanding of their structural and functional organization, their interaction with vessels and nerves, the layout of paracrine interactions, and the relationship between subcellular compartments and protein complexes inside each cell. These elements are not static; they are dynamic and exert their biological actions at different scales of time. Therefore, scientists must be able to investigate (and visualize) short- and long-lived events within the pancreas and β-cells. Current technological advances in microscopy are able to bridge multiple spatiotemporal scales in biology to reveal the complexity and heterogeneity of β-cell biology. Here, I briefly discuss the historical discoveries that leveraged microscopes to establish the basis of β-cell anatomy and structure, the current imaging platforms that allow the study of islet and β-cell biology at multiple scales of resolution, and their challenges and implications. Lastly, I outline how the remarkable longevity of structural elements at different scales in biology, from molecules to cells to multicellular structures, could represent a previously unrecognized organizational pattern in developing and adult β-cells and pancreas biology.

Single-cell-resolved differentiation of human induced pluripotent stem cells into pancreatic duct-like organoids on a microwell chip

Creating in vitro models of diseases of the pancreatic ductal compartment requires a comprehensive understanding of the developmental trajectories of pancreas-specific cell types. Here we report the single-cell characterization of the differentiation of pancreatic duct-like organoids (PDLOs) from human induced pluripotent stem cells (hiPSCs) on a microwell chip that facilitates the uniform aggregation and chemical induction of hiPSC-derived pancreatic progenitors. Using time-resolved single-cell transcriptional profiling and immunofluorescence imaging of the forming PDLOs, we identified differentiation routes from pancreatic progenitors through ductal intermediates to two types of mature duct-like cells and a few non-ductal cell types. PDLO subpopulations expressed either mucins or the cystic fibrosis transmembrane conductance regulator, and resembled human adult duct cells. We also used the chip to uncover ductal markers relevant to pancreatic carcinogenesis, and to establish PDLO co-cultures with stellate cells, which allowed for the study of epithelial-mesenchymal signalling. The PDLO microsystem could be used to establish patient-specific pancreatic duct models.

Ptf1a function and transcriptional cis-regulation, a cornerstone in vertebrate pancreas development

Vertebrate pancreas organogenesis is a stepwise process regulated by a complex network of signaling and transcriptional events, progressively steering the early endoderm toward pancreatic fate. Many crucial players of this process have been identified, including signaling pathways, cis‐regulatory elements, and transcription factors (TFs). Pancreas‐associated transcription factor 1a (PTF1A) is one such TF, crucial for pancreas development. PTF1A mutations result in dramatic pancreatic phenotypes associated with severe complications, such as neonatal diabetes and impaired food digestion due to exocrine pancreatic insufficiency. Here, we present a brief overview of vertebrate pancreas development, centered on Ptf1a function and transcriptional regulation, covering similarities and divergences in three broadly studied organisms: human, mouse and zebrafish.

Pancreatic β-cell heterogeneity in health and diabetes: classes, sources, and subtypes

Pancreatic β-cells perform glucose-stimulated insulin secretion, a process at the center of type 2 diabetes etiology. Efforts to understand how β-cells behave in healthy and stressful conditions have revealed a wide degree of morphological, functional, and transcriptional heterogeneity. Sources of heterogeneity include β-cell topography, developmental origin, maturation state, and stress response. Advances in sequencing and imaging technologies have led to the identification of β-cell subtypes, which play distinct roles in the islet niche. This review examines β-cell heterogeneity from morphological, functional, and transcriptional perspectives, and considers the relevance of topography, maturation, development, and stress response. It also discusses how these factors have been used to identify β-cell subtypes, and how heterogeneity is impacted by diabetes. We examine open questions in the field and discuss recent technological innovations that could advance understanding of β-cell heterogeneity in health and disease.

Characterization of a bicistronic knock-in reporter mouse model for investigating the role of CABLES2 in vivo

Two members of the CDK5 and ABL enzyme substrate (CABLES) family, CABLES1 and CABLES2, share a highly homologous C-terminus. They interact and associate with cyclin-dependent kinase 3 (CDK3), CDK5, and c-ABL. CABLES1 mediates tumor suppression, regulates cell proliferation, and prevents protein degradation. Although Cables2 is ubiquitously expressed in adult mouse tissues at RNA level, the role of CABLES2 in vivo remains unknown. Here, we generated bicistronic Cables2 knock-in reporter mice that expressed CABLES2 tagged with 3×FLAG and 2A-mediated fluorescent reporter tdTomato. Cables2-3×FLAG-2A-tdTomato (Cables2Tom) mice confirmed the expression of Cables2 in various mouse tissues. Interestingly, high intensity of tdTomato fluorescence was observed in the brain, testis and ovary, especially in the corpus luteum. Furthermore, immunoprecipitation analysis using the brain and testis in Cables2Tom/Tom revealed interaction of CABLES2 with CDK5. Collectively, our new Cables2 knock-in reporter model will enable the comprehensive analysis of in vivo CABLES2 function.

SMAD7 enhances adult β-cell proliferation without significantly affecting β-cell function in mice

The interplay between the transforming growth factor β (TGF-β) signaling proteins, SMAD family member 2 (SMAD2) and 3 (SMAD3), and the TGF-β-inhibiting SMAD, SMAD7, seems to play a vital role in proper pancreatic endocrine development and also in normal β-cell function in adult pancreatic islets. Here, we generated conditional SMAD7 knockout mice by crossing insulin1^Cre mice with SMAD7^fx/fx mice. We also created a β cell-specific SMAD7-overexpressing mouse line by crossing insulin1^Dre mice with HPRT-SMAD7/RosaGFP mice. We analyzed β-cell function in adult islets when SMAD7 was either absent or overexpressed in β cells. Loss of SMAD7 in β cells inhibited proliferation, and SMAD7 overexpression enhanced cell proliferation. However, alterations in basic glucose homeostasis were not detectable following either SMAD7 deletion or overexpression in β cells. Our results show that both the absence and overexpression of SMAD7 affect TGF-β signaling and modulates β-cell proliferation but does not appear to alter β-cell function. Reversible SMAD7 overexpression may represent an attractive therapeutic option to enhance β-cell proliferation without negative effects on β-cell function.