Encapsulated human islets in alginate fiber maintain long-term functionality

Maintenance of islet function after in vitro culture is crucial for both transplantation and research. Here we evaluated the effects of encapsulation in alginate fiber on the function of human islets which were distributed by the Alberta Islet Distribution Program. Encapsulated human islets from 15 deceased donors were cultured under 5.5 or 25 mM glucose conditions in vitro. The amounts of C-peptide and glucagon secreted from encapsulated islets into the culture media were measured periodically, and immunohistochemical studies were performed. Encapsulated islets maintained C-peptide and glucagon secretion for more than 75 days in 5 cases; in two cases, their secretion was also successfully detected even on day 180. α- and β-cell composition and β-cell survival in islets were unaltered in the fiber after 75 or 180 days of culture. The encapsulated islets cultured with 5.5 mM glucose, but not those with 25 mM glucose, exhibited glucose responsiveness of C-peptide secretion until day 180. We demonstrate that alginate encapsulation enabled human islets to maintain their viability and glucose responsiveness of C-peptide secretion after long-term in vitro culture, potentially for more than for 180 days.

Single-nucleus RNA sequencing of human pancreatic islets identifies novel gene sets and distinguishes β-cell subpopulations with dynamic transcriptome profiles

BACKGROUND

Single-cell RNA sequencing (scRNA-seq) provides valuable insights into human islet cell types and their corresponding stable gene expression profiles. However, this approach requires cell dissociation that complicates its utility in vivo. On the other hand, single-nucleus RNA sequencing (snRNA-seq) has compatibility with frozen samples, elimination of dissociation-induced transcriptional stress responses, and affords enhanced information from intronic sequences that can be leveraged to identify pre-mRNA transcripts.

METHODS

We obtained nuclear preparations from fresh human islet cells and generated snRNA-seq datasets. We compared these datasets to scRNA-seq output obtained from human islet cells from the same donor. We employed snRNA-seq to obtain the transcriptomic profile of human islets engrafted in immunodeficient mice. In both analyses, we included the intronic reads in the snRNA-seq data with the GRCh38-2020-A library.

RESULTS

First, snRNA-seq analysis shows that the top four differentially and selectively expressed genes in human islet endocrine cells in vitro and in vivo are not the canonical genes but a new set of non-canonical gene markers including ZNF385D, TRPM3, LRFN2, PLUT (β-cells); PTPRT, FAP, PDK4, LOXL4 (α-cells); LRFN5, ADARB2, ERBB4, KCNT2 (δ-cells); and CACNA2D3, THSD7A, CNTNAP5, RBFOX3 (γ-cells). Second, by integrating information from scRNA-seq and snRNA-seq of human islet cells, we distinguish three β-cell sub-clusters: an INS pre-mRNA cluster (β3), an intermediate INS mRNA cluster (β2), and an INS mRNA-rich cluster (β1). These display distinct gene expression patterns representing different biological dynamic states both in vitro and in vivo. Interestingly, the INS mRNA-rich cluster (β1) becomes the predominant sub-cluster in vivo.

CONCLUSIONS

In summary, snRNA-seq and pre-mRNA analysis of human islet cells can accurately identify human islet cell populations, subpopulations, and their dynamic transcriptome profile in vivo.

Local islet remodelling associated with duct lesion-islet complex in adult human pancreas

AIMS/HYPOTHESIS

Islets are thought to be stably present in the adult human pancreas to maintain glucose homeostasis. However, identification of the pancreatic intraepithelial neoplasia (PanIN)-islet complex in mice and the presence of PanIN lesions in adult humans suggest that similar remodelling of islet structure and environment may occur in the human pancreas. To identify islet remodelling in a clinically related setting, we examine human donor pancreases with 3D histology to detect and characterise the human PanIN-islet complex.

METHODS

Cadaveric donor pancreases (26-65 years old, n = 10) were fixed and sectioned (350 μm) for tissue labelling, clearing and microscopy to detect local islet remodelling for 3D analysis of the microenvironment. The remodelled microenvironment was subsequently examined via microtome-based histology for clinical assessment.

RESULTS

In nine pancreases, we identified the unique peri-lobular islet aggregation associated with the PanIN lesion (16 lesion-islet complexes detected; size: 3.18 ± 1.34 mm). Important features of the lesion-islet microenvironment include: (1) formation of intra-islet ducts, (2) acinar atrophy, (3) adipocyte association, (4) inflammation (CD45⁺), (5) stromal accumulation (α-SMA⁺), (6) increase in Ki-67 proliferation index but absence of Ki-67⁺ alpha/beta cells and (7) in-depth and continuous duct-islet cell contacts, forming a cluster. The duct-islet cell cluster and intra-islet ducts suggest likely islet cell neogenesis but not replication.

CONCLUSIONS/INTERPRETATION

We identify local islet remodelling associated with PanIN-islet complex in the adult human pancreas. The tissue remodelling and the evidence of inflammation and stromal accumulation suggest that the PanIN-islet complex is derived from tissue repair after a local injury.

Single-cell transcriptomics of human islet ontogeny defines the molecular basis of β-cell dedifferentiation in T2D

OBJECTIVE

Dedifferentiation of pancreatic β-cells may reduce islet function in type 2 diabetes (T2D). However, the prevalence, plasticity and functional consequences of this cellular state remain unknown.

METHODS

We employed single-cell RNAseq to detail the maturation program of α- and β-cells during human ontogeny. We also compared islets from non-diabetic and T2D individuals.

RESULTS

Both α- and β-cells mature in part by repressing non-endocrine genes; however, α-cells retain hallmarks of an immature state, while β-cells attain a full β-cell specific gene expression program. In islets from T2D donors, both α- and β-cells have a less mature expression profile, de-repressing the juvenile genetic program and exocrine genes and increasing expression of exocytosis, inflammation and stress response signalling pathways. These changes are consistent with the increased proportion of β-cells displaying suboptimal function observed in T2D islets.

CONCLUSIONS

These findings provide new insights into the molecular program underlying islet cell maturation during human ontogeny and the loss of transcriptomic maturity that occurs in islets of type 2 diabetics.

Significant reduction of apoptosis induced via hypoxia and oxidative stress in isolated human islet by resveratrol

BACKGROUND AND AIMS

Successful islet transplantation as a promising treatment of diabetes type 1 is threatened with the loss of islets during the pre-transplant culture due to hypoxia and oxidative stress-induced apoptosis. Therefore, optimization of culture in order to preserve the islets is a critical point. In this study, we investigated the effect of resveratrol, as a cytoprotective agent, on the cultured human islets.

METHODS AND RESULTS

Isolated islets were treated with different concentrations of resveratrol for 24 and 72 h. Islets' viability, apoptosis, apoptosis markers, and insulin and C-peptide secretion, along with the production of reactive oxygen species (ROS), hypoxia inducible factor 1 alpha (HIF-1α), and its target genes in the islets were investigated. Our findings showed that the islets were exposed to hypoxia and oxidative stress after isolation and during culture. This insult induced apoptosis and decreased viability during 72 h. The presence of resveratrol significantly attenuated HIF-1α and ROS production, reduced apoptosis, promoted the VEGF secretion, and increased the insulin and C-peptide secretion. In this regard, resveratrol improved the islet's survival and function in the culture period.

CONCLUSIONS

Using resveratrol can attenuate the stressful condition for the islets in the pre-transplant culture and subsequently ameliorate their viability and functionality that lead to successful outcome after clinical transplantation.

Recruited fibroblasts reconstitute the peri-islet membrane: a longitudinal imaging study of human islet grafting and revascularisation

AIMS/HYPOTHESIS

Rapid and adequate islet revascularisation and restoration of the islet-extracellular matrix (ECM) interaction are significant factors influencing islet survival and function of the transplanted islets in individuals with type 1 diabetes. Because the ECM encapsulating the islets is degraded during islet isolation, understanding the process of revascularisation and engraftment after transplantation is essential and needs further investigation.

METHODS

Here we apply a longitudinal and high-resolution imaging approach to investigate the dynamics of the pancreatic islet engraftment process up to 11 months after transplantation. Human and mouse islet grafts were inserted into the anterior chamber of the mouse eye, using a NOD.ROSA-tomato.Rag2^-/- or B6.ROSA-tomato host allowing the investigation of the expansion of host vs donor cells and the contribution of host cells to aspects such as promoting the encapsulation and vascularisation of the graft.

RESULTS

A fibroblast-like stromal cell population of host origin rapidly migrates to ensheath the transplanted islet and aid in the formation of a basement membrane-like structure. Moreover, we show that the vessel network, while reconstituted by host endothelial cells, still retains the overall architecture of the donor islets.

CONCLUSIONS/INTERPRETATION

In this transplantation situation the fibroblast-like stromal cells appear to take over as main producers of ECM or act as a scaffold for other ECM-producing cells to reconstitute a peri-islet-like basement membrane. This may have implications for our understanding of long-term graft rejection and for the design of novel strategies to interfere with this process.

Biophysical modeling of β-cells networks: Realistic architectures and heterogeneity effects

The β-cells dynamics is the regulator of insulin secretion in the pancreas, and its investigation is a central aspect in designing effective treatment strategies for diabetes. Despite great efforts, much is still unknown about the complex organization of such endocrine cells and realistic mathematical modeling represents a useful tool to elucidate key aspects of glucose control in humans. In this contribution, we study the human β-cells collective behaviour, by modeling their electric and metabolic coupling in a cluster, of size and architecture similar to human islets of Langerhans. We focus on the effect of coupling on various dynamics regimes observed in the islets, that are spiking and bursting on multiple timescales. In particular, we test the effect of hubs, that are highly glucose-sensitive β-cells, on the overall network dynamics, observing different modulation depending on the timescale of the dynamics. By properly taking into account the role of cells heterogeneity, recently emerged, our model effectively describes the effect of hubs on the synchronization of the islet response and the correlation of β-cells activity.

Human pancreatic neuro-insular network in health and fatty infiltration

AIMS/HYPOTHESIS

Identification of a pancreatic neuro-insular network in mice suggests that a similar integration of islets and nerves may be present in the human pancreas. To characterise the neuro-insular network and the intra-pancreatic ganglia in a clinically related setting, we examined human pancreases in health and with fatty infiltration via 3-dimensional (3D) histology and compared the human pancreatic microenvironment with its counterpart in mice.

METHODS

Human pancreatic specimens from individuals with normal BMI, high BMI (≥ 25) and type 2 diabetes were used to investigate the neuro-insular network. Transparent specimens were prepared by tissue clearing for transmitted light and deep-tissue fluorescence imaging to simultaneously visualise infiltrated adipocytes, islets and neurovascular networks.

RESULTS

High-definition images of human islets reveal that both the sympathetic and parasympathetic nerves enter the islet core and reside in the immediate microenvironment of islet cells. Around the islets, the neuro-insular network is visualised with 3D histology to identify the intra-pancreatic ganglia (peri-lobular and intra-parenchymal ganglia) and the islet-ganglionic association. In humans, but not in mice, pancreatic fatty infiltration (BMI dependent) features adipocytes infiltrating into the parenchyma and accumulating in the peri-lobular space, in which the peri-lobular ganglia also reside. We identified the formation of adipose-ganglionic complexes in the peri-lobular space and enlargement of ganglia around adipocytes. In the specimen from the individual with type 2 diabetes, an increase in the number of nerve projections from the intra-parenchymal ganglia is associated with severe fatty infiltration.

CONCLUSIONS/INTERPRETATION

We present new perspectives of human pancreas and islet innervation via 3D histology. Our results strongly suggest that fatty infiltration in the human pancreas creates a neurotrophic microenvironment and promotes remodelling of pancreatic innervation.

The Biochemical Cascades of the Human Pancreatic β-Cells: The Role of MicroRNAs

Diabetes mellitus is a disease that poses a burden to the health care system due to its prevalence and chronic nature. Understanding β cell pathophysiology may lead to future therapeutic options for diabetes mellitus type 1 and 2. MicroRNAs (MiR) fine-tune β cell biochemical cascades through specific protein targets. This review argues that miRs may play a critical role in human islet β cell biology and are potential candidates for a new pharmacological strategy. We have reviewed and presented how miRs fine tune four biochemical cascades in islet β cells: glucose stimulated insulin secretion, β cell replication, apoptosis, and development. Only studies that examine human pancreatic islets either in vitro or in vivo are included. The unveiling role of miR pathways in regulating human islet β cell biology could open the door for diagnostic and therapeutic methods for diabetes mellitus prevention and therapy.

Isolation and characterization of human islet stellate cells

BACKGROUND AND AIMS

We have previously demonstrated that islet stellate cells (ISCs) exhibiting a similar phenotype to classical pancreatic stellate cells (PSCs) could be isolated from rat islets, where they may contribute to islet fibrosis in type 2 diabetes mellitus (T2DM). This study was designed to determine whether human islets also contain ISC.

MATERIALS AND METHODS

Using standard explants techniques, human ISCs were enriched from freshly isolated human islets. Immunofluorescence visualization of markers for PSCs(α-smooth muscle actin;α-SMA), desmin, vimentin, glial fibrillary acidic protein (GFAP) was used to characterize the human ISC. Cell counting kit-8 (CCK-8) was used to assess the proliferation of ISC. The wound-healing assay and the transwell migration were used to assess the migration capacity of ISC. Immunofluorescence against collagen typesI (col-I), collagen typesIII (col-III) and fibronectin (FN) was performed to identify extracellular matrix (ECM) component synthesized by ISC. Adipogenic and osteogenic differentiation were tried to detected stem cell potential.

RESULTS

In culture, ISC with triangular shape grow out from human islets. The passaged ISC expressed α-SMA, desmin, vimentin, GFAP and was positive for col-I, col-III and FN. The proliferation and migration ability of ISC was significantly slower than those of PSC. And both the human PSC and ISC were able to differentiate in vitro into adipocyte- and osteoblast-like cells.

CONCLUSION

Similar to our previous rat experiment, the current study shows that human islets also contain ISC which is phenotypically similar but not identical to human PSC.

Anti-apoptotic Effects of Bone Marrow on Human Islets: A Preliminary Report

Apoptosis is one of the major factors contributing to the failure of human islet transplantation. Contributors to islet apoptosis exist in both the pre-transplantation and post transplantation stages. Factors include the islet isolation process, deterioration in vitro prior to transplantation, and immune rejection post transplantation. Previous studies have demonstrated that co-cultured bone marrow cells with human islets not only significantly enhanced the longevity of human islets but also maintained function. We hypothesized that the protective effects of bone marrow cells on human islets are through mechanisms related to preventing apoptosis. This study observed the levels of inflammatory factors such as interleukin-1β (IL-1β), the release of extracellular ATP in vitro, and expression levels of P2X7 ATP receptor (P2X7R), all of which lead to the occurrence of apoptosis in human islets. When human islets were co-cultured with human bone marrow, there was a reduction in the rate of apoptosis correlated with the reduction in inflammatory factors, extra cellular ATP accumulation, and ATP receptor P2X7R expression versus human islets cultured alone. These results suggest that co-culturing bone marrow cells with human islets inhibits inflammation and reduces apoptosis, thus protecting islets from self-deterioration.

A possible role of transglutaminase 2 in the nucleus of INS-1E and of cells of human pancreatic islets

Transglutaminase 2 (TG2) is a multifunctional protein with Ca^2 +-dependent transamidating and G protein activity. Previously we reported that the role of TG2 in insulin secretion may involve cytoplasmic actin remodeling and a regulative action on other proteins during granule movement. The aim of this study was to gain a better insight into the role of TG2 transamidating activity in mitochondria and in the nucleus of INS-1E rat insulinoma cell line (INS-1E) during insulin secretion. To this end we labeled INS-1E with an artificial donor (biotinylated peptide), in basal condition and after stimulus with glucose for 2, 5, and 8 min. Biotinylated proteins of the nuclear/mitochondrial-enriched fraction were analyzed using two-dimensional electrophoresis and mass spectrometry. Many mitochondrial proteins involved in Ca^2 + homeostasis (e.g. voltage-dependent anion-selective channel protein, prohibitin and different ATP synthase subunits) and many nuclear proteins involved in gene regulation (e.g. histone H3, barrier to autointegration factor and various heterogeneous nuclear ribonucleoprotein) were identified among a number of transamidating substrates of TG2 in INS-1E. The combined results provide evidence that a temporal link exists between glucose-stimulation, first phase insulin secretion and the action of TG on histone H3 both in INS-1E and human pancreatic islets.

Biological significance

Research into the role of transglutaminase 2 during insulin secretion in INS-1E rat insulinoma cellular model is depicting a complex role for this enzyme. Transglutaminase 2 acts in the different INS-1E compartments in the same way: catalyzing a post-translational modification event of its substrates. In this work we identify some mitochondrial and nuclear substrates of INS-1E during first phase insulin secretion. The finding that TG2 interacts with nuclear proteins that include BAF and histone H3 immediately after (2–5 min) glucose stimulus of INS-1E suggests that TG2 may be involved not only in insulin secretion, as suggested by our previous studies in cytoplasmic INS-1E fraction, but also in the regulation of glucose-induced gene transcription.

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Transglutaminase 2 localizes in the nucleus and in the mitochondrion of INS-1E.

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TG2 acts as a modifying enzyme in both compartments during FPIS.

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TG2 may contribute to Ca^2 + sensing in mitochondrion through its substrates.

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TG2 may contribute to chromatin condensation in nucleus through its substrates.

PAK1 limits the expression of the pro-apoptotic protein Bad in pancreatic islet β-cells

Human type 2 diabetes is associated with β-cell apoptosis, and human islets from diabetic donors are ∼80% deficient in PAK1 protein. Toward addressing linkage of PAK1 to β-cell survival, PAK1–siRNA targeted MIN6 pancreatic β-cells were found to exhibit increased caspase-3 cleavage, cytosolic cytochrome-C and the pro-apoptotic protein Bad. PAK1^+/− heterozygous mouse islets recapitulated the upregulation of Bad protein expression, as did hyperglycemic treatment of human or mouse islets; Bad levels were exacerbated most in PAK1^+/− islets subjected to hyperglycemic stress. These data implicate PAK1 in β-cell survival via quenching of Bad protein expression, and suggest PAK1 as potential molecular target to preserve β-cell mass.