Islet hypertrophy following pancreatic disruption of Smad4 signaling

Lipotoxicity Induces β-cell Small Extracellular Vesicle-Mediated β-cell Dysfunction in Male Mice

Chronically elevated circulating excess free fatty acids (ie, lipotoxicity) is a pathological process implicated in several metabolic disorders, including obesity-driven type 2 diabetes (T2D). Lipotoxicity exerts detrimental effects on pancreatic islet β-cells by reducing glucose-stimulated insulin secretion (GSIS), altering β-cell transcriptional identity, and promoting apoptosis. While β-cell-derived small extracellular vesicles (sEV) have been shown to contribute to β-cell failure in T2D, their specific role in lipotoxicity-mediated β-cell failure remains to be elucidated. In this work, we demonstrate that lipotoxicity enhances the release of sEVs from β-cells, which exhibit altered proteomic and lipidomic profiles. These palmitate (PAL)-exposed extracellular vesicles (EVs) induce β-cell dysfunction in healthy mouse and human islets and trigger significant islet transcriptional changes, including the upregulation of genes associated with the TGFβ/Smad3 pathway, as noted by RNA sequencing. Importantly, pharmacological inhibition of the TGFβI/II receptor improved PAL EV-induced β-cell dysfunction, underscoring their involvement in activating the TGFβ/Smad3 pathway during this process. We have comprehensively characterized lipotoxic β-cell sEVs and implicated their role in inducing β-cell functional failure in T2D. These findings highlight potential avenues for therapeutic interventions targeting sEV-mediated pathways to preserve β-cell health in metabolic disorders.

Smad4 Heterozygous Knockout Effect on Pancreatic and Body Weight in F1 Population Using Collaborative Cross Lines

Smad4, a critical tumor suppressor gene, plays a significant role in pancreatic biology and tumorigenesis. Genetic background and sex are known to influence phenotypic outcomes, but their impact on pancreatic weight in Smad4-deficient mice remains unclear. This study investigates the impact of Smad4 deficiency on pancreatic weight in first-generation (F1) mice from diverse collaborative cross (CC) lines, focusing on the influence of genetic background and sex. F1 mice were generated by crossbreeding female CC mice with C57BL/6J-Smad4tm1Mak males. Genotyping confirmed the presence of Smad4 knockout alleles. Mice were housed under standard conditions, euthanized at 80 weeks, and their pancreatic weights were measured, adjusted for body weight, and analyzed for effects of Smad4 deficiency, sex, and genetic background. The overall population of F1 mice showed a slight but non-significant increase in adjusted pancreatic weights in heterozygous knockout mice compared to wild-type mice. Sex-specific analysis revealed no significant difference in males but a significant increase in adjusted pancreatic weights in heterozygous knockout females. Genetic background analysis showed that lines CC018 and CC025 substantially increased adjusted pancreatic weights in heterozygous knockout mice. In contrast, other lines showed no significant difference or varied non-significant changes. The interplay between genetic background and sex further influenced these outcomes. Smad4 deficiency affects pancreatic weight in a manner significantly modulated by genetic background and sex. This study highlights the necessity of considering these factors in genetic research and therapeutic development, demonstrating the value of the collaborative cross mouse population in dissecting complex genetic interactions.

VGLL4 and MENIN function as TEAD1 corepressors to block pancreatic β cell proliferation

TEAD1 and the mammalian Hippo pathway regulate cellular proliferation and function, though their regulatory function in β cells remains poorly characterized. In this study, we demonstrate that while β cell-specific TEAD1 deletion results in a cell-autonomous increase of β cell proliferation, β cell-specific deletion of its canonical coactivators, YAP and TAZ, does not affect proliferation, suggesting the involvement of other cofactors. Using an improved split-GFP system and yeast two-hybrid platform, we identify VGLL4 and MENIN as TEAD1 corepressors in β cells. We show that VGLL4 and MENIN bind to TEAD1 and repress the expression of target genes, including FZD7 and CCN2, which leads to an inhibition of β cell proliferation. In conclusion, we demonstrate that TEAD1 plays a critical role in β cell proliferation and identify VGLL4 and MENIN as TEAD1 corepressors in β cells. We propose that these could be targeted to augment proliferation in β cells for reversing diabetes.

Bioengineered Pancreas-Liver Crosstalk in a Microfluidic Coculture Chip Identifies Human Metabolic Response Signatures in Prediabetic Hyperglycemia

Aberrant glucose homeostasis is the most common metabolic disturbance affecting one in ten adults worldwide. Prediabetic hyperglycemia due to dysfunctional interactions between different human tissues, including pancreas and liver, constitutes the largest risk factor for the development of type 2 diabetes. However, this early stage of metabolic disease has received relatively little attention. Microphysiological tissue models that emulate tissue crosstalk offer emerging opportunities to study metabolic interactions. Here, a novel modular multitissue organ-on-a-chip device is presented that allows for integrated and reciprocal communication between different 3D primary human tissue cultures. Precisely controlled heterologous perfusion of each tissue chamber is achieved through a microfluidic single "synthetic heart" pneumatic actuation unit connected to multiple tissue chambers via specific configuration of microchannel resistances. On-chip coculture experiments of organotypic primary human liver spheroids and intact primary human islets demonstrate insulin secretion and hepatic insulin response dynamics at physiological timescales upon glucose challenge. Integration of transcriptomic analyses with promoter motif activity data of 503 transcription factors reveals tissue-specific interacting molecular networks that underlie β-cell stress in prediabetic hyperglycemia. Interestingly, liver and islet cultures show surprising counter-regulation of transcriptional programs, emphasizing the power of microphysiological coculture to elucidate the systems biology of metabolic crosstalk.

Role of TGF-Beta Signaling in Beta Cell Proliferation and Function in Diabetes

Beta (β) cell dysfunction or loss is the common pathological feature in all types of diabetes mellitus (diabetes). Resolving the underlying mechanism may facilitate the treatment of diabetes by preserving the β cell population and function. It is known that TGF-β signaling plays diverse roles in β cell development, function, proliferation, apoptosis, and dedifferentiation. Inhibition of TGF-β signaling expands β cell lineage in the development. However, deletion of Tgfbr1 has no influence on insulin demand-induced but abolishes inflammation-induced β cell proliferation. Among canonical TGF-β signaling, Smad3 but not Smad2 is the predominant repressor of β cell proliferation in response to systemic insulin demand. Deletion of Smad3 simultaneously improves β cell function, apoptosis, and systemic insulin resistance with the consequence of eliminated overt diabetes in diabetic mouse models, revealing Smad3 as a key mediator and ideal therapeutic target for type-2 diabetes. However, Smad7 shows controversial effects on β cell proliferation and glucose homeostasis in animal studies. On the other hand, overexpression of Tgfb1 prevents β cells from autoimmune destruction without influence on β cell function. All these findings reveal the diverse regulatory roles of TGF-β signaling in β cell biology.

Combined inhibition of menin-MLL interaction and TGF-β signaling induces replication of human pancreatic beta cells

Both type 1 and type 2 diabetes are associated with hyperglycemia and loss of functional beta cell mass. Inducing proliferation of preexisting beta cells is an approach to increase the numbers of beta cells. In this study, we examined a panel of selected small molecules for their proliferation-inducing effects on human pancreatic beta cells. Our results demonstrated that a small molecule inhibitor of the menin-MLL interaction (MI-2) and small molecule inhibitors of TGF-β signaling (SB431542, LY2157299, or LY364947) synergistically increased ex vivo replication of human beta cells. We showed that this increased proliferation did not affect insulin production, as a pivotal indication of beta cell function. We further provided evidence which suggested that menin-MLL and TGF-β inhibition cooperated through downregulation of cell cycle inhibitors CDKN1A, CDKN1B, and CDKN2C. Our findings might provide a new option for extending the pharmacological repertoire for induction of beta cell proliferation as a potential therapeutic approach for diabetes.

Zebrafish model of KRAS-initiated pancreatic endocrine tumor

Pancreatic cancer constitutes a genetic disease in which somatic mutations in the KRAS proto-oncogene are detected in 95% of cases. Activation of the KRAS proto-oncogene represents an initiating event in pancreatic tumorigenesis. Here, we established a zebrafish pancreatic neoplasia model that recapitulates human pancreatic tumors. Toward this end, we generated a stable CRE/Lox-based zebrafish model system to express oncogenic KRAS^G12D in the elastase3I domain of the zebrafish pancreas. Lineage tracing experiments showed that early KRAS^G12D-responsive pancreatic progenitors contribute to endocrine in addition to exocrine cells. In this system, 10% and 40% of zebrafish developed pancreatic tumors by 6 and 12 months, respectively. The histological profiles of these experimental tumors bore a striking resemblance to those of pancreatic endocrine tumors. Immunohistochemical analysis including the endocrine cell-specific marker confirmed the pancreatic tumor region as a characteristic endocrine tumor. Taken together, our zebrafish model data revealed that pancreatic endocrine tumors originate from early KRAS^G12D-responsive pancreatic progenitor cells. These findings demonstrated that this zebrafish model may be suitable as an experimental and preclinical system to evaluate different strategies for targeting pancreatic endocrine tumors and ultimately improve the outcome for patients with pancreatic endocrine tumors.

Developing a network view of type 2 diabetes risk pathways through integration of genetic, genomic and functional data

BACKGROUND

Genome-wide association studies (GWAS) have identified several hundred susceptibility loci for type 2 diabetes (T2D). One critical, but unresolved, issue concerns the extent to which the mechanisms through which these diverse signals influencing T2D predisposition converge on a limited set of biological processes. However, the causal variants identified by GWAS mostly fall into a non-coding sequence, complicating the task of defining the effector transcripts through which they operate.

METHODS

Here, we describe implementation of an analytical pipeline to address this question. First, we integrate multiple sources of genetic, genomic and biological data to assign positional candidacy scores to the genes that map to T2D GWAS signals. Second, we introduce genes with high scores as seeds within a network optimization algorithm (the asymmetric prize-collecting Steiner tree approach) which uses external, experimentally confirmed protein-protein interaction (PPI) data to generate high-confidence sub-networks. Third, we use GWAS data to test the T2D association enrichment of the "non-seed" proteins introduced into the network, as a measure of the overall functional connectivity of the network.

RESULTS

We find (a) non-seed proteins in the T2D protein-interaction network so generated (comprising 705 nodes) are enriched for association to T2D (p = 0.0014) but not control traits, (b) stronger T2D-enrichment for islets than other tissues when we use RNA expression data to generate tissue-specific PPI networks and (c) enhanced enrichment (p = 3.9 × 10^- 5) when we combine the analysis of the islet-specific PPI network with a focus on the subset of T2D GWAS loci which act through defective insulin secretion.

CONCLUSIONS

These analyses reveal a pattern of non-random functional connectivity between candidate causal genes at T2D GWAS loci and highlight the products of genes including YWHAG, SMAD4 or CDK2 as potential contributors to T2D-relevant islet dysfunction. The approach we describe can be applied to other complex genetic and genomic datasets, facilitating integration of diverse data types into disease-associated networks.

Inhibition of TGF-β Signaling Promotes Human Pancreatic β-Cell Replication

Diabetes is associated with loss of functional pancreatic β-cells, and restoration of β-cells is a major goal for regenerative therapies. Endogenous regeneration of β-cells via β-cell replication has the potential to restore cellular mass; however, pharmacological agents that promote regeneration or expansion of endogenous β-cells have been elusive. The regenerative capacity of β-cells declines rapidly with age, due to accumulation of p16(INK4a), resulting in limited capacity for adult endocrine pancreas regeneration. Here, we show that transforming growth factor-β (TGF-β) signaling via Smad3 integrates with the trithorax complex to activate and maintain Ink4a expression to prevent β-cell replication. Importantly, inhibition of TGF-β signaling can result in repression of the Ink4a/Arf locus, resulting in increased β-cell replication in adult mice. Furthermore, small molecule inhibitors of the TGF-β pathway promote β-cell replication in human islets transplanted into NOD-scid IL-2Rg(null) mice. These data reveal a novel role for TGF-β signaling in the regulation of the Ink4a/Arf locus and highlight the potential of using small molecule inhibitors of TGF-β signaling to promote human β-cell replication.

Monosodium Glutamate Dietary Consumption Decreases Pancreatic β-Cell Mass in Adult Wistar Rats

Background

The amount of dietary monosodium glutamate (MSG) is increasing worldwide, in parallel with the epidemics of metabolic syndrome. Parenteral administration of MSG to rodents induces obesity, hyperglycemia, hyperlipidemia, insulin resistance, and type 2 diabetes. However, the impact of dietary MSG is still being debated. We investigated the morphological and functional effects of prolonged MSG consumption on rat glucose metabolism and on pancreatic islet histology.

Methods

Eighty adult male Wistar rats were randomly subdivided into 4 groups, and test rats in each group were supplemented with MSG for a different duration (1, 3, 6, or 9 months, n=20 for each group). All rats were fed ad libitum with a standard rat chow and water. Ten test rats in each group were provided MSG 2 mg/g body weight/day in drinking water and the 10 remaining rats in each group served as non-MSG treated controls. Oral glucose tolerance tests (OGTT) were performed and serum insulin measured at 9 months. Animals were sacrificed at 1, 3, 6, or 9 months to examine the histopathology of pancreatic islets.

Results

MSG-treated rats had significantly lower pancreatic β-cell mass at 1, 6 and 9 months of study. Islet hemorrhages increased with age in all groups and fibrosis was significantly more frequent in MSG-treated rats at 1 and 3 months. Serum insulin levels and glucose tolerance in MSG-treated and untreated rats were similar at all time points we investigated.

Conclusion

Daily MSG dietary consumption was associated with reduced pancreatic β-cell mass and enhanced hemorrhages and fibrosis, but did not affect glucose homeostasis. We speculate that high dietary MSG intake may exert a negative effect on the pancreas and such effect might become functionally significant in the presence or susceptibility to diabetes or NaCl; future experiments will take these crucial cofactors into account.

Developmental biology of the pancreas: a comprehensive review

Pancreatic development represents a fascinating process in which two morphologically distinct tissue types must derive from one simple epithelium. These two tissue types, exocrine (including acinar cells, centro-acinar cells, and ducts) and endocrine cells serve disparate functions, and have entirely different morphology. In addition, the endocrine tissue must become disconnected from the epithelial lining during its development. The pancreatic development field has exploded in recent years, and numerous published reviews have dealt specifically with only recent findings, or specifically with certain aspects of pancreatic development. Here I wish to present a more comprehensive review of all aspects of pancreatic development, though still there is not a room for discussion of stem cell differentiation to pancreas, nor for discussion of post-natal regeneration phenomena, two important fields closely related to pancreatic development.

Unique mechanisms of growth regulation and tumor suppression upon Apc inactivation in the pancreas

beta-catenin signaling is heavily involved in organogenesis. Here, we investigated how pancreas differentiation, growth and homeostasis are affected following inactivation of an endogenous inhibitor of beta-catenin, adenomatous polyposis coli (Apc). In adult mice, Apc-deficient pancreata were enlarged, solely as a result of hyperplasia of acinar cells, which accumulated beta-catenin, with the sparing of islets. Expression of a target of beta-catenin, the proto-oncogene c-myc (Myc), was increased in acinar cells lacking Apc, suggesting that c-myc expression is essential for hyperplasia. In support of this hypothesis, we found that conditional inactivation of c-myc in pancreata lacking Apc completely reversed the acinar hyperplasia. Apc loss in organs such as the liver, colon and kidney, as well as experimental misexpression of c-myc in pancreatic acinar cells, led to tumor formation with high penetrance. Surprisingly, pancreas tumors failed to develop following conditional pancreas Apc inactivation. In Apc-deficient acini of aged mice, our studies revealed a cessation of their exaggerated proliferation and a reduced expression of c-myc, in spite of the persistent accumulation of beta-catenin. In conclusion, our work shows that beta-catenin modulation of c-myc is an essential regulator of acinar growth control, and unveils an unprecedented example of Apc requirement in the pancreas that is both temporally restricted and cell-specific. This provides new insights into the mechanisms of tumor pathogenesis and tumor suppression in the pancreas.

Smad4 is dispensable for normal pancreas development yet critical in progression and tumor biology of pancreas cancer

SMAD4 is inactivated in the majority of pancreatic ductal adenocarcinomas (PDAC) with concurrent mutational inactivation of the INK4A/ARF tumor suppressor locus and activation of the KRAS oncogene. Here, using genetically engineered mice, we determined the impact of SMAD4 deficiency on the development of the pancreas and on the initiation and/or progression of PDAC-alone or in combination with PDAC--relevant mutations. Selective SMAD4 deletion in the pancreatic epithelium had no discernable impact on pancreatic development or physiology. However, when combined with the activated KRAS(G12D) allele, SMAD4 deficiency enabled rapid progression of KRAS(G12D)-initiated neoplasms. While KRAS(G12D) alone elicited premalignant pancreatic intraepithelial neoplasia (PanIN) that progressed slowly to carcinoma, the combination of KRAS(G12D) and SMAD4 deficiency resulted in the rapid development of tumors resembling intraductal papillary mucinous neoplasia (IPMN), a precursor to PDAC in humans. SMAD4 deficiency also accelerated PDAC development of KRAS(G12D) INK4A/ARF heterozygous mice and altered the tumor phenotype; while tumors with intact SMAD4 frequently exhibited epithelial-to-mesenchymal transition (EMT), PDAC null for SMAD4 retained a differentiated histopathology with increased expression of epithelial markers. SMAD4 status in PDAC cell lines was associated with differential responses to transforming growth factor-beta (TGF-beta) in vitro with a subset of SMAD4 wild-type lines showing prominent TGF-beta-induced proliferation and migration. These results provide genetic confirmation that SMAD4 is a PDAC tumor suppressor, functioning to block the progression of KRAS(G12D)-initiated neoplasms, whereas in a subset of advanced tumors, intact SMAD4 facilitates EMT and TGF-beta-dependent growth.