Browsing by Author "Spaeth, Jason M."

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    The Chd4 subunit of the NuRD complex regulates Pdx1-controlled genes involved in β-cell function
    (Bioscientifica, 2022-06-14) Davidson, Rebecca K.; Weaver, Staci A.; Casey, Nolan; Kanojia, Sukrati; Hogarth, Elise; Schneider Aguirre, Rebecca; Sims, Emily K.; Evans-Molina, Carmella; Spaeth, Jason M.; Biochemistry and Molecular Biology, School of Medicine
    Type 2 diabetes (T2D) is associated with loss of transcription factors (TFs) from a subset of failing β-cells. Among these TFs is Pdx1, which controls the expression of numerous genes involved in maintaining β-cell function and identity. Pdx1 activity is modulated by transcriptional coregulators and has recently been shown, through an unbiased screen, to interact with the Chd4 ATPase subunit of the nucleosome remodeling and deacetylase complex. Chd4 contributes to the maintenance of cellular identity and functional status of numerous different cell types. Here, we demonstrated that Pdx1 dynamically interacts with Chd4 under physiological and stimulatory conditions within islet β-cells and established a fundamental role for Chd4 in regulating insulin secretion and modulating numerous Pdx1-bound genes in vitro, including the MafA TF, where we discovered Chd4 is bound to the MafA region 3 enhancer. Furthermore, we found that Pdx1:Chd4 interactions are significantly compromised in islet β-cells under metabolically induced stress in vivo and in human donor tissues with T2D. Our findings establish a fundamental role for Chd4 in regulating insulin secretion and modulating Pdx1-bound genes in vitro, and disruption of Pdx1:Chd4 interactions coincides with β-cell dysfunction associated with T2D.
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    The Contribution of Transcriptional Coregulators in the Maintenance of β-cell Function and Identity
    (Endocrine Society, 2021) Davidson, Rebecca K.; Kanojia, Sukrati; Spaeth, Jason M.; Biochemistry and Molecular Biology, School of Medicine
    Islet β-cell dysfunction that leads to impaired insulin secretion is a principal source of pathology of diabetes. In type 2 diabetes, this breakdown in β-cell health is associated with compromised islet-enriched transcription factor (TF) activity that disrupts gene expression programs essential for cell function and identity. TF activity is modulated by recruited coregulators that govern activation and/or repression of target gene expression, thereby providing a supporting layer of control. To date, more than 350 coregulators have been discovered that coordinate nucleosome rearrangements, modify histones, and physically bridge general transcriptional machinery to recruited TFs; however, relatively few have been attributed to β-cell function. Here, we will describe recent findings on those coregulators with direct roles in maintaining islet β-cell health and identity and discuss how disruption of coregulator activity is associated with diabetes pathogenesis.
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    Dynamic regulation of pancreatic β cell function and gene expression by the SND1 coregulator in vitro
    (Taylor & Francis, 2023) Kanojia, Sukrati; Davidson, Rebecca K.; Conley, Jason M.; Xu, Jerry; Osmulski, Meredith; Sims, Emily K.; Ren, Hongxia; Spaeth, Jason M.; Biochemistry and Molecular Biology, School of Medicine
    The pancreatic β cell synthesizes, packages, and secretes insulin in response to glucose-stimulation to maintain blood glucose homeostasis. Under diabetic conditions, a subset of β cells fail and lose expression of key transcription factors (TFs) required for insulin secretion. Among these TFs is Pancreatic and duodenal homeobox 1 (PDX1), which recruits a unique subset of transcriptional coregulators to modulate its activity. Here we describe a novel interacting partner of PDX1, the Staphylococcal Nuclease and Tudor domain-containing protein (SND1), which has been shown to facilitate protein-protein interactions and transcriptional control through diverse mechanisms in a variety of tissues. PDX1:SND1 interactions were confirmed in rodent β cell lines, mouse islets, and human islets. Utilizing CRISPR-Cas9 gene editing technology, we deleted Snd1 from the mouse β cell lines, which revealed numerous differentially expressed genes linked to insulin secretion and cell proliferation, including limited expression of Glp1r. We observed Snd1 deficient β cell lines had reduced cell expansion rates, GLP1R protein levels, and limited cAMP accumulation under stimulatory conditions, and further show that acute ablation of Snd1 impaired insulin secretion in rodent and human β cell lines. Lastly, we discovered that PDX1:SND1 interactions were profoundly reduced in human β cells from donors with type 2 diabetes (T2D). These observations suggest the PDX1:SND1 complex formation is critical for controlling a subset of genes important for β cell function and is targeted in diabetes pathogenesis.
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    The Chd4 Helicase Regulates Chromatin Accessibility and Gene Expression Critical for β-Cell Function In Vivo
    (American Diabetes Association, 2023) Davidson, Rebecca K.; Kanojia, Sukrati; Wu, Wenting; Kono, Tatsuyoshi; Xu, Jerry; Osmulski, Meredith; Bone, Robert N.; Casey, Nolan; Evans-Molina, Carmella; Sims, Emily K.; Spaeth, Jason M.; Biochemistry and Molecular Biology, School of Medicine
    The transcriptional activity of Pdx1 is modulated by a diverse array of coregulatory factors that govern chromatin accessibility, histone modifications, and nucleosome distribution. We previously identified the Chd4 subunit of the nucleosome remodeling and deacetylase complex as a Pdx1-interacting factor. To identify how loss of Chd4 impacts glucose homeostasis and gene expression programs in β-cells in vivo, we generated an inducible β-cell-specific Chd4 knockout mouse model. Removal of Chd4 from mature islet β-cells rendered mutant animals glucose intolerant, in part due to defects in insulin secretion. We observed an increased ratio of immature-to-mature insulin granules in Chd4-deficient β-cells that correlated with elevated levels of proinsulin both within isolated islets and from plasma following glucose stimulation in vivo. RNA sequencing and assay for transposase-accessible chromatin with sequencing showed that lineage-labeled Chd4-deficient β-cells have alterations in chromatin accessibility and altered expression of genes critical for β-cell function, including MafA, Slc2a2, Chga, and Chgb. Knockdown of CHD4 from a human β-cell line revealed similar defects in insulin secretion and alterations in several β-cell-enriched gene targets. These results illustrate how critical Chd4 activities are in controlling genes essential for maintaining β-cell function. Article highlights: Pdx1-Chd4 interactions were previously shown to be compromised in β-cells from human donors with type 2 diabetes. β-Cell-specific removal of Chd4 impairs insulin secretion and leads to glucose intolerance in mice. Expression of key β-cell functional genes and chromatin accessibility are compromised in Chd4-deficient β-cells. Chromatin remodeling activities enacted by Chd4 are essential for β-cell function under normal physiological conditions.
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    The Yin and Yang of Modulating β-Cell DNA Damage Response and Functional Mass
    (American Diabetes Association, 2022) Spaeth, Jason M.; Dhawan, Sangeeta; Biochemistry and Molecular Biology, School of Medicine