Biology subjects

Sussel, L.

Publications and source records attributed to Sussel, L..

9 recordsLinked to original sources

bioRxiv2026

Carbamylome analysis reveals regulatory roles for lysine carbamylation in β-cell glycolytic and insulin-processing enzymes

In type 1 diabetes (T1D), insulin-producing {beta} cells are destroyed by an autoimmune response driven by pro-inflammatory cytokines, including interferons. {beta}-cell cytokine signaling is mediated in part by post-translational modifications, such as phosphorylation and acetylation. However, the role of other post-translational modifications in {beta}-cell cytokine signaling represents an important knowledge gap. In the context of autoimmune diseases, lysine carbamylation has gained attention for its role in pathogenesis. Here, we investigate the role of carbamylation in T1D. We found that pancreatic islet cells from the T1D model, non-obese diabetic (NOD) mice, exhibit 11% carbamylation-positive cells, whereas non-diabetic CD1 mice have only 5%. Proteomics analysis of the MIN6 insulin-producing cell line treated with a cocktail of three pro-inflammatory cytokines IFN{gamma} + IL-1{beta} + TNF identified 284 carbamylated peptides from 222 proteins impacted by the cytokine treatment. Integration of carbamylation and acetylation provided a deep view of the cytokine-regulated PTMs and potential points of interplay. A functional-enrichment analysis revealed that carbamylation was enriched in pathways related to autoimmune diseases, metabolism, DNA replication, and protein translation. Moreover, functional testing demonstrated that carbamylation inhibits the glycolytic enzyme aldolase A and the insulin-processing enzyme carboxypeptidase E, identifying a possible role for cytokine-induced {beta}-cell dysfunction. In summary, protein carbamylation is elevated in islets from NOD mice, and pro-inflammatory cytokine treatment regulates protein carbamylation in MIN6 cells. These data identify carbamylation as a potential regulatory mechanism for {beta}-cell metabolism and insulin production in the context of islet inflammation.

biochemistry↗

bioRxiv2025

Human NKX2.2 influences islet endocrine cell fate choices through regulation of WNT pathway genes

Transcriptional regulation is a key central mechanism of cell fate determination in developing tissues. The homeobox transcription factor NKX2.2 is an essential regulator of mouse and human pancreatic endocrine development, however its precise molecular role in a human system has not been previously investigated. In this study we generated NKX2.2 null (NKX2.2KO) human embryonic stem cell (hESC) lines using CRISPR/Cas9 technologies and differentiated them towards a pancreatic {beta} cell fate using a stem cell-derived {beta} cell differentiation protocol. Functional and transcriptomic analyses of the hESC-derived pancreatic endocrine cells lacking NKX2.2 revealed similarities and differences compared to the molecular functions of NKX2.2 in mice. In the absence of NKX2.2, the {beta} cell differentiations result in reduced numbers of insulin-producing cells, and the differentiations become skewed towards polyhormonal fates, including cells co-expressing insulin, ghrelin and somatostatin. Deletion of NKX2.2 also eliminates the off-target formation of enterochromaffin cells. Single cell transcriptome analysis of the early endocrine cell population revealed a marked disruption of metabolic pathways that was confirmed by comparative metabolite tracing, providing novel insights into the regulation of early endocrine lineage decisions. Furthermore, NKX2.2 directly regulates several genes in the WNT signaling pathway, suggesting this is a key molecular mechanism through which NKX2.2 regulates these islet cell fate decisions in the human system.

developmental biology↗

bioRxiv2025

The Chromatin Remodeler Protein CHD4 Cooperates With NKX2.2 to Regulate Pancreatic Beta Cell Integrity

NKX2.2 is a transcription factor that regulates pancreatic islet beta ({beta}) cell identity and function; however, cofactor proteins that modulate the functional activity of NKX2.2 in {beta} cells are relatively unexplored. An unbiased proteomics screen identified chromodomain helicase DNA-binding protein 4 (CHD4) as an NKX2.2 interacting partner. CHD4 is a nucleosome remodeler that directs the appropriate differentiation, maturation and function of many cell types. To characterize the roles of CHD4 in {beta} cells, we generated Chd4 {beta}KO mice. Deletion of Chd4 substantially impaired the function of {beta} cells. The Chd4 {beta}KO mice became diabetic due to the disruption of islet integrity, calcium signaling and downregulation of essential {beta} cell regulatory genes. We also discovered CHD4 is required to bind at and repress non-beta cell genes, including Kcnj5, the gene that encodes the GIRK4 potassium channel in {beta} cells. Aberrant upregulation of GIRK4 causes impaired glucose-stimulated insulin secretion. These studies demonstrate that CHD4 is an essential transcriptional cofactor of NKX2.2 that is required for the proper maturation and function of pancreatic {beta} cells. Article HighlightsO_LINKX2.2 interacts with the Nucleosome Remodeling and Deacetylase (NuRD) complex through its interaction with CHD4. C_LIO_LIDeletion of CHD4 from developing pancreatic {beta} cells in mice causes diabetes due to a loss of islet integrity, disrupted calcium signaling and impaired insulin secretion. C_LIO_LIBeta cells lacking CHD4 inappropriately upregulate the GIRK4 potassium channel; inhibition of GIRK4 rescues the insulin secretion defect. C_LI

developmental biology↗

bioRxiv2025

Optimizing Single-Cell Long-Read Sequencing for Enhanced Isoform Detection in Pancreatic Islets

Alternative splicing is an essential mechanism for generating protein diversity by producing distinct isoforms from a single gene. Dysregulation of splicing that affects pancreatic function and immune tolerance has been linked to both type 1 and type 2 diabetes. Next-generation sequencing technologies, with their short read lengths, are limited in their ability to accurately detect splice variants. Long-read sequencing technologies offer the potential to overcome these limitations by providing full-length transcript information; however, their application in single-cell RNA sequencing has been hindered by technical challenges, including insufficient read lengths and higher error rates. Furthermore, cell types that produce high levels of a single transcript, such as islet endocrine cells, can obscure identification of lower abundance transcripts. In this study, we optimized a protocol for single-cell long-read sequencing in pancreatic islets to improve read length and transcript detection. Our findings demonstrate that 5 library preparation protocols outperform 3 protocols, resulting in better transcript identification. Furthermore, we show that targeted depletion of insulin transcripts enhances the detection of informative reads, highlighting the utility of transcript depletion strategies. This optimized protocol enables isoform-specific gene expression analysis and reveals differential transcript usage across the various cell types in pancreatic islets. By leveraging this approach, we gain deeper insights into the transcriptomic complexity and cellular heterogeneity within pancreatic islets. Article HighlightsO_LIThis study addresses the limitations of current single-cell long-read RNA-sequencing (sclrRNA-seq) technologies in detecting full-length transcripts and isoform diversity, particularly in pancreatic islets. C_LIO_LIWe demonstrate that optimizing single-cell library preparation protocols reproducibly enhances read length and transcript identification in pancreatic islets. C_LIO_LI5 capture methods, combined with targeted insulin depletion and extended reverse transcription, significantly improved read length and isoform detection compared to standard protocols, while maximizing the number of informative reads. C_LIO_LIThese improvements yield longer reads in single-cell experiments, substantially enhancing transcript identification and enabling more accurate analysis of isoform diversity. C_LI

genomics↗

bioRxiv2024

NKX2.2 and KLF4 cooperate to regulate alpha cell identity

Transcription factors (TFs) are indispensable for maintaining cell identity through regulating cell-specific gene expression. Distinct cell identities derived from a common progenitor are frequently perpetuated by shared TFs; yet the mechanisms that enable these TFs to regulate cell-specific targets are poorly characterized. We report that the TF NKX2.2 is critical for the identity of pancreatic islet cells by directly activating cell genes and repressing alternate islet cell fate genes. When compared to the known role of NKX2.2 in islet {beta} cells, we demonstrate that NKX2.2 regulates cell genes, facilitated in part by cell specific DNA binding at gene promoters. Furthermore, we have identified the reprogramming factor KLF4 as having enriched expression in cells, where it co-occupies NKX2.2-bound cell promoters, is necessary for NKX2.2 promoter occupancy in cells and co-regulates many NKX2.2 cell transcriptional targets. Misexpression of Klf4 in {beta} cells is sufficient to manipulate chromatin accessibility, increase binding of NKX2.2 at cell specific promoter sites, and alter expression of NKX2.2-regulated cell-specific targets. This study identifies KLF4 is a novel cell factor that cooperates with NKX2.2 to regulate cell identity.

developmental biology↗

bioRxiv2024

Meningeal-derived retinoic acid regulates neurogenesis via suppression of Notch and Sox2

The meninges act as a regulator of brain development by secreting ligands that act on neural cells to regulate neurogenesis and neuronal migration. Meningeal-derived retinoic acid (RA) promotes neocortical neural progenitor cell cycle exit; however, the underlying molecular mechanism is unknown. Here, we used spatial transcriptomics and profiling of retinoic-acid receptor- (RAR) DNA binding in Foxc1-mutant embryos that lack meninges-derived ligands to identify the neurogenic transcriptional mechanisms of RA signaling in telencephalic neural progenitors. We determined that meningeal-derived RA controls neurogenesis by suppressing progenitor self-renewal pathways Notch signaling and the transcription factor Sox2. We show that RAR binds in the Sox2ot promoter, a long non-coding RNA that regulates Sox2 expression, and RA promotes Sox2ot expression in neocortical progenitors. Our findings elucidate a previously unknown mechanism of how meningeal RA coordinates neocortical development and insight into how defects in meningeal development may cause neurodevelopmental disorders.

neuroscience↗

bioRxiv2024

Reduction of chemokine CXCL9 expression by omega-3 fatty acids via ADP-ribosylhydrolase ARH3 in MIN6 insulin-producing cells

Type 1 diabetes (T1D) results from the autoimmune destruction of the insulin producing {beta} cells of the pancreas. Omega-3 fatty acids protect {beta} cells and reduce the incident of T1D. However, how omega-3 fatty acids act on {beta} cells is not well understood. We have shown that omega-3 fatty acids reduce pro-inflammatory cytokine-mediated {beta}-cell apoptosis by upregulating the expression of the ADP-ribosylhydrolase ARH3. Here, we further investigate the {beta}-cell protection mechanism by ARH3 by performing siRNA of its gene Adprhl2 in MIN6 insulin-producing cells followed by treatment with a cocktail of the pro-inflammatory cytokines IL-1{beta} + IFN-{gamma} + TNF-, and proteomics analysis. ARH3 regulated proteins from several pathways related to the nucleus (splicing, RNA surveillance and nucleocytoplasmic transport), mitochondria (metabolic pathways) and endoplasmic reticulum (protein folding). ARH3 also regulated the levels of cytokine-signaling proteins related to the antigen processing and presentation, and chemokine-signaling pathway. We further studied the role of ARH in regulating the chemokine CXCL9. We confirmed that ARH3 reduces the cytokine-induced expression of CXCL9 by ELISA. We also found that CXCL9 expression is regulated by omega-3 fatty acids. In conclusion, we showed that omega-3 fatty acids regulate CXCL9 expression via ARH3, which might have a role in protecting {beta} cells from immune attack and preventing T1D development.

cell biology↗

bioRxiv2022

Retrograde mitochondrial signaling governs the identity and maturity of metabolic tissues

Mitochondrial damage is a hallmark of metabolic diseases, including diabetes and metabolic dysfunction-associated steatotic liver disease, yet the consequences of impaired mitochondria in metabolic tissues are often unclear. Here, we report that dysfunctional mitochondrial quality control engages a retrograde (mitonuclear) signaling program that impairs cellular identity and maturity across multiple metabolic tissues. Surprisingly, we demonstrate that defects in the mitochondrial quality control machinery, which we observe in pancreatic {beta} cells of humans with type 2 diabetes, cause reductions of {beta} cell mass due to dedifferentiation, rather than apoptosis. Utilizing transcriptomic profiling, lineage tracing, and assessments of chromatin accessibility, we find that targeted deficiency anywhere in the mitochondrial quality control pathway (e.g., genome integrity, dynamics, or turnover) activate the mitochondrial integrated stress response and promote cellular immaturity in {beta} cells, hepatocytes, and brown adipocytes. Intriguingly, pharmacologic blockade of mitochondrial retrograde signaling in vivo restores {beta} cell mass and identity to ameliorate hyperglycemia following mitochondrial damage. Thus, we observe that a shared mitochondrial retrograde response controls cellular identity across metabolic tissues and may be a promising target to treat or prevent metabolic disorders.

cell biology↗

bioRxiv2020

The role of islet lipid composition remodeling in regulation of beta-cell death via ADP-ribosyl-acceptor glycohydrolase ARH3 signaling in insulitis

Lipids have been implicated as mediators of insulitis and {beta}-cell death in type 1 diabetes development, but the mechanisms underlying this association are poorly understood. Here, we investigated the changes in islet/{beta}-cell lipid composition using three models of insulitis: human islets and EndoC-{beta}H1 {beta}-cells treated with the cytokines IL-1{beta} and IFN-{gamma}, and islets from non-obese diabetic mice. Across all three models, lipidomic analyses showed a consistent change in abundance of the lysophosphatidylcholine, phosphatidylcholine and triacylglycerol species. We also showed that lysophosphatidylcholine and its biosynthetic enzyme PLA2G6 are enriched in murine islets. We determined that the ADP-ribosyl-acceptor glycohydrolase ARH3 is regulated by cytokines downstream of PLA2G6, which in turn regulates proteins involved in apoptosis, lipid metabolism, antigen processing and presentation and chemokines. ARH3 reduced cytokine-induced apoptosis, which may represent a negative feedback mechanism. Overall, these data show the importance of lipid metabolism in regulating {beta}-cell death in type 1 diabetes. HighlightsO_LILipidomics of 3 insulitis models revealed commonly regulated lipid classes. C_LIO_LIIdentification of 35 proteins regulated by cytokines via PLA2G6 signaling. C_LIO_LIARH3 reduces cytokine-induced apoptosis via PLA2G6 regulation. C_LIO_LIARH3 regulates the levels of proteins related to insulitis and type 1 diabetes. C_LI

systems biology↗