IU Indianapolis ScholarWorks :: Browsing by Author "Anderson, Ryan M."

Browsing by Author "Anderson, Ryan M."

Now showing 1 - 10 of 20

12-Lipoxygenase governs the innate immune pathogenesis of islet inflammation and autoimmune diabetes
(The American Society for Clinical Investigation, 2021-07-22) Kulkarni, Abhishek; Pineros, Annie R.; Walsh, Melissa A.; Casimiro, Isabel; Ibrahim, Sara; Hernandez-Perez, Marimar; Orr, Kara S.; Glenn, Lindsey; Nadler, Jerry L.; Morris, Margaret A.; Tersey, Sarah A.; Mirmira, Raghavendra G.; Anderson, Ryan M.; Pediatrics, School of Medicine
Macrophages and related myeloid cells are innate immune cells that participate in the early islet inflammation of type 1 diabetes (T1D). The enzyme 12-lipoxygenase (12-LOX) catalyzes the formation of proinflammatory eicosanoids, but its role and mechanisms in myeloid cells in the pathogenesis of islet inflammation have not been elucidated. Leveraging a model of islet inflammation in zebrafish, we show here that macrophages contribute significantly to the loss of β cells and the subsequent development of hyperglycemia. The depletion or inhibition of 12-LOX in this model resulted in reduced macrophage infiltration into islets and the preservation of β cell mass. In NOD mice, the deletion of the gene encoding 12-LOX in the myeloid lineage resulted in reduced insulitis with reductions in proinflammatory macrophages, a suppressed T cell response, preserved β cell mass, and almost complete protection from the development of T1D. 12-LOX depletion caused a defect in myeloid cell migration, a function required for immune surveillance and tissue injury responses. This effect on migration resulted from the loss of the chemokine receptor CXCR3. Transgenic expression of the gene encoding CXCR3 rescued the migratory defect in zebrafish 12-LOX morphants. Taken together, our results reveal a formative role for innate immune cells in the early pathogenesis of T1D and identify 12-LOX as an enzyme required to promote their prodiabetogenic phenotype in the context of autoimmunity.
A 12-lipoxygenase-Gpr31 signaling axis is required for pancreatic organogenesis in the zebrafish
(Wiley, 2020-11) Hernandez-Perez, Marimar; Kulkarni, Abhishek; Samala, Niharika; Sorrell, Cody; El, Kimberly; Haider, Isra; Aleem, Ansari Mukhtar; Holman, Theodore R.; Rai, Ganesha; Tersey, Sarah A.; Mirmira, Raghavendra G.; Anderson, Ryan M.; Pediatrics, School of Medicine
12-Lipoxygenase (12-LOX) is a key enzyme in arachidonic acid metabolism, and alongside its major product, 12-HETE, plays a key role in promoting inflammatory signaling during diabetes pathogenesis. Although 12-LOX is a proposed therapeutic target to protect pancreatic islets in the setting of diabetes, little is known about the consequences of blocking its enzymatic activity during embryonic development. Here, we have leveraged the strengths of the zebrafish-genetic manipulation and pharmacologic inhibition-to interrogate the role of 12-LOX in pancreatic development. Lipidomics analysis during zebrafish development demonstrated that 12-LOX-generated metabolites of arachidonic acid increase sharply during organogenesis stages, and that this increase is blocked by morpholino-directed depletion of 12-LOX. Furthermore, we found that either depletion or inhibition of 12-LOX impairs both exocrine pancreas growth and unexpectedly, the generation of insulin-producing β cells. We demonstrate that morpholino-mediated knockdown of GPR31, a purported G-protein-coupled receptor for 12-HETE, largely phenocopies both the depletion and the inhibition of 12-LOX. Moreover, we show that loss of GPR31 impairs pancreatic bud fusion and pancreatic duct morphogenesis. Together, these data provide new insight into the requirement of 12-LOX in pancreatic organogenesis and islet formation, and additionally provide evidence that its effects are mediated via a signaling axis that includes the 12-HETE receptor GPR31.
Characterization of Ethanol-induced Effects on Zebrafish Retinal Development: Mechanistic Perspective and Therapeutic Strategies
(2016) Muralidharan, Pooja; Marrs, James A.; Leung, Yuk Fai; Belecky-Adams, Teri; Meyer, Jason; Anderson, Ryan M.; Randall, Stephen K.
Fetal alcohol spectrum disorder (FASD) is a result of prenatal alcohol exposure, producing a wide range of defects including craniofacial, sensory, motor and cognitive deficits. Many ocular abnormalities are frequently associated with FASD including microphthalmia, optic nerve hypoplasia, and cataracts. FASD is highly prevalent in low socioeconomic populations, where it is also accompanied by higher rates of malnutrition and alcoholism. Using zebrafish as a model to study FASD retinal defects has been extremely insightful in understanding the ethanol-induced retinal defects at the cellular level. Zebrafish embryos treated with ethanol from mid-blastula transition through somitogenesis (2-24 hours post fertilization; hpf) showed defects similar to human ocular deficits including microphthalmia, optic nerve hypoplasia, and photoreceptor differentiation defects. Ethanol exposure altered critical transcription factor expression involved in retinal cell differentiation. Retinoic acid (RA) and folic acid (FA) nutrient co-supplementation rescued optic nerve and photoreceptor differentiation defects. Ethanol exposure during retinal morphogenesis stages (16-24 hpf), produced retinal defects like those seen with ethanol exposure between 2-24 hpf. Significantly, during ethanol-sensitive time window (16-24 hpf), RA co-supplementation moderately rescued these defects, whereas, FA cosupplementation showed significant rescue of optic nerve and photoreceptor differentiation. RA, but not FA, supplementation after ethanol exposure could restore ethanol-induced optic nerve and photoreceptor differentiation defects. Ethanol exposure did not affect timing of retinal cell differentiation induction, but later increased retinal cell death and proliferation. Ethanol-treated embryos showed increased retinal proliferation in the outer nuclear layer (ONL), inner nuclear layer (INL), and ciliary marginal zone (CMZ) at 48 hpf and 72 hpf. In order to identify the genesis of ethanol-induced persistent retinal defects, ethanol effects on retinal stem cell populations in the CMZ and the Müller glial cells (MGCs) were examined. Ethanol treated retinas had an expanded CMZ indicated by histology and Alcama, a retinal stem cell marker, immunolabeling, but reduced expression of rx1 and the cell cycle exit marker, cdkn1c. Ethanol treated retinas also showed reduced MGCs. At 72 hpf, ONL of ethanol exposed fish showed fewer photoreceptors expressing terminal differentiation markers. Importantly, these poorly differentiated photoreceptors co-expressed the basic helix-loop-helix (bHLH) proneural differentiation factor, neurod, indicating that ethanol exposure produced immature and undifferentiated photoreceptors. Reduced differentiation along with increased progenitor marker expression and proliferation suggest cell cycle exit failure due to ethanol exposure. These results suggested that ethanol exposure disrupted stem cell differentiation progression. Wnt, Notch and proneural gene expression regulate retinal stem cell proliferation and transition into progenitor cells. Ethanol exposure disrupted Wnt activity in the CMZ as well as Notch activity and neurod gene expression in the retina. RA and FA co-supplementation were able to rescue Wnt activity in the CMZ and rescue downstream Notch activity. To test whether the rescue of these Wnt-active cells could restore the retinal cell differentiation pathways, ethanol treated embryos were treated with Wnt agonist. This treatment could restore Wnt-active cells in the CMZ, Notch-active cells in the retina, proliferation, and photoreceptor terminal differentiation. We conclude that ethanol exposure produced persistent defects in the stem cell Wnt signaling, a critical pathway in retinal cell differentiation. Further analysis of underlying molecular mechanisms will provide insight into the embryonic origins of ethanol-induced retinal defects and potential therapeutic targets to cure this disorder.
Coordinating cardiomyocyte interactions to direct ventricular chamber morphogenesis
(SpringerNature, 2016-06-30) Han, Peidong; Bloomekatz, Joshua; Ren, Jie; Zhang, Ruilin; Grinstein, Jonathan D.; Zhao, Long; Burns, C. Geoffrey; Burns, Caroline E.; Anderson, Ryan M.; Chi, Neil C.; Department of Pediatrics, IU School of Medicine
Many organs are composed of complex tissue walls that are structurally organized to optimize organ function. In particular, the ventricular myocardial wall of the heart comprises an outer compact layer that concentrically encircles the ridge-like inner trabecular layer. Although disruption in the morphogenesis of this myocardial wall can lead to various forms of congenital heart disease and non-compaction cardiomyopathies, it remains unclear how embryonic cardiomyocytes assemble to form ventricular wall layers of appropriate spatial dimensions and myocardial mass. Here we use advanced genetic and imaging tools in zebrafish to reveal an interplay between myocardial Notch and Erbb2 signalling that directs the spatial allocation of myocardial cells to their proper morphological positions in the ventricular wall. Although previous studies have shown that endocardial Notch signalling non-cell-autonomously promotes myocardial trabeculation through Erbb2 and bone morphogenetic protein (BMP) signalling, we discover that distinct ventricular cardiomyocyte clusters exhibit myocardial Notch activity that cell-autonomously inhibits Erbb2 signalling and prevents cardiomyocyte sprouting and trabeculation. Myocardial-specific Notch inactivation leads to ventricles of reduced size and increased wall thickness because of excessive trabeculae, whereas widespread myocardial Notch activity results in ventricles of increased size with a single-cell-thick wall but no trabeculae. Notably, this myocardial Notch signalling is activated non-cell-autonomously by neighbouring Erbb2-activated cardiomyocytes that sprout and form nascent trabeculae. Thus, these findings support an interactive cellular feedback process that guides the assembly of cardiomyocytes to morphologically create the ventricular myocardial wall and more broadly provide insight into the cellular dynamics of how diverse cell lineages organize to create form.
Deoxyhypusine Synthase Promotes a Pro-Inflammatory Macrophage Phenotype
(Elsevier, 2021) Anderson-Baucum, Emily; Piñeros, Annie R.; Kulkarni, Abhishek; Webb-Robertson, Bobbie-Jo; Maier, Bernhard; Anderson, Ryan M.; Wu, Wenting; Tersey, Sarah A.; Mastracci, Teresa L.; Casimiro, Isabel; Scheuner, Donalyn; Metz, Thomas O.; Nakayasu, Ernesto S.; Evans-Molina, Carmella; Mirmira, Raghavendra G.; Biology, School of Science
The metabolic inflammation (meta-inflammation) of obesity is characterized by proinflammatory macrophage infiltration into adipose tissue. Catalysis by deoxyhypusine synthase (DHPS) modifies the translation factor eIF5A to generate a hypusine (Hyp) residue. Hypusinated eIF5A (eIF5AHyp) controls the translation of mRNAs involved in inflammation, but its role in meta-inflammation has not been elucidated. Levels of eIF5AHyp were found to be increased in adipose tissue macrophages from obese mice and in murine macrophages activated to a proinflammatory M1-like state. Global proteomics and transcriptomics revealed that DHPS deficiency in macrophages altered the abundance of proteins involved in NF-κB signaling, likely through translational control of their respective mRNAs. DHPS deficiency in myeloid cells of obese mice suppressed M1 macrophage accumulation in adipose tissue and improved glucose tolerance. These findings indicate that DHPS promotes the post-transcriptional regulation of a subset of mRNAs governing inflammation and chemotaxis in macrophages and contributes to a proinflammatory M1-like phenotype.
Glucagon is essential for alpha cell transdifferentiation and beta cell neogenesis
(The Company of Biologists, 2015-04-15) Ye, Lihua; Robertson, Morgan A.; Hesselson, Daniel; Stainier, Didier Y. R.; Anderson, Ryan M.; Department of Pediatrics, IU School of Medicine
The interconversion of cell lineages via transdifferentiation is an adaptive mode of tissue regeneration and an appealing therapeutic target. However, its clinical exploitation is contingent upon the discovery of contextual regulators of cell fate acquisition and maintenance. In murine models of diabetes, glucagon-secreting alpha cells transdifferentiate into insulin-secreting beta cells following targeted beta cell depletion, regenerating the form and function of the pancreatic islet. However, the molecular triggers of this mode of regeneration are unknown. Here, using lineage-tracing assays in a transgenic zebrafish model of beta cell ablation, we demonstrate conserved plasticity of alpha cells during islet regeneration. In addition, we show that glucagon expression is upregulated after injury. Through gene knockdown and rescue approaches, we also find that peptides derived from the glucagon gene are necessary for alpha-to-beta cell fate switching. Importantly, whereas beta cell neogenesis was stimulated by glucose, alpha-to-beta cell conversion was not, suggesting that transdifferentiation is not mediated by glucagon/GLP-1 control of hepatic glucose production. Overall, this study supports the hypothesis that alpha cells are an endogenous reservoir of potential new beta cells. It further reveals that glucagon plays an important role in maintaining endocrine cell homeostasis through feedback mechanisms that govern cell fate stability.
An In Vivo Zebrafish Model for Interrogating ROS-Mediated Pancreatic β-Cell Injury, Response, and Prevention
(Hindawi Publishing Corporation, 2018-03-28) Kulkarni, Abhishek A.; Conteh, Abass M.; Sorrell, Cody A.; Mirmira, Anjali; Tersey, Sarah A.; Mirmira, Raghavendra G.; Linnemann, Amelia K.; Anderson, Ryan M.; Biochemistry and Molecular Biology, School of Medicine
It is well known that a chronic state of elevated reactive oxygen species (ROS) in pancreatic β-cells impairs their ability to release insulin in response to elevated plasma glucose. Moreover, at its extreme, unmitigated ROS drives regulated cell death. This dysfunctional state of ROS buildup can result both from genetic predisposition and environmental factors such as obesity and overnutrition. Importantly, excessive ROS buildup may underlie metabolic pathologies such as type 2 diabetes mellitus. The ability to monitor ROS dynamics in β-cells in situ and to manipulate it via genetic, pharmacological, and environmental means would accelerate the development of novel therapeutics that could abate this pathology. Currently, there is a lack of models with these attributes that are available to the field. In this study, we use a zebrafish model to demonstrate that ROS can be generated in a β-cell-specific manner using a hybrid chemical genetic approach. Using a transgenic nitroreductase-expressing zebrafish line, Tg(ins:Flag-NTR)s950 , treated with the prodrug metronidazole (MTZ), we found that ROS is rapidly and explicitly generated in β-cells. Furthermore, the level of ROS generated was proportional to the dosage of prodrug added to the system. At high doses of MTZ, caspase 3 was rapidly cleaved, β-cells underwent regulated cell death, and macrophages were recruited to the islet to phagocytose the debris. Based on our findings, we propose a model for the mechanism of NTR/MTZ action in transgenic eukaryotic cells and demonstrate the robust utility of this system to model ROS-related disease pathology.
Inhibition of 12/15-Lipoxygenase Protects Against β-Cell Oxidative Stress and Glycemic Deterioration in Mouse Models of Type 1 Diabetes
(American Diabetes Association, 2017-11) Hernandez-Perez, Marimar; Chopra, Gaurav; Fine, Jonathan; Conteh, Abass M.; Anderson, Ryan M.; Linnemann, Amelia K.; Benjamin, Chanelle; Nelson, Jennifer B.; Benninger, Kara S.; Nadler, Jerry L.; Maloney, David J.; Tersey, Sarah A.; Mirmira, Raghavendra G.; Pediatrics, School of Medicine
Islet β-cell dysfunction and aggressive macrophage activity are early features in the pathogenesis of type 1 diabetes (T1D). 12/15-Lipoxygenase (12/15-LOX) is induced in β-cells and macrophages during T1D and produces proinflammatory lipids and lipid peroxides that exacerbate β-cell dysfunction and macrophage activity. Inhibition of 12/15-LOX provides a potential therapeutic approach to prevent glycemic deterioration in T1D. Two inhibitors recently identified by our groups through screening efforts, ML127 and ML351, have been shown to selectively target 12/15-LOX with high potency. Only ML351 exhibited no apparent toxicity across a range of concentrations in mouse islets, and molecular modeling has suggested reduced promiscuity of ML351 compared with ML127. In mouse islets, incubation with ML351 improved glucose-stimulated insulin secretion in the presence of proinflammatory cytokines and triggered gene expression pathways responsive to oxidative stress and cell death. Consistent with a role for 12/15-LOX in promoting oxidative stress, its chemical inhibition reduced production of reactive oxygen species in both mouse and human islets in vitro. In a streptozotocin-induced model of T1D in mice, ML351 prevented the development of diabetes, with coincident enhancement of nuclear Nrf2 in islet cells, reduced β-cell oxidative stress, and preservation of β-cell mass. In the nonobese diabetic mouse model of T1D, administration of ML351 during the prediabetic phase prevented dysglycemia, reduced β-cell oxidative stress, and increased the proportion of anti-inflammatory macrophages in insulitis. The data provide the first evidence to date that small molecules that target 12/15-LOX can prevent progression of β-cell dysfunction and glycemic deterioration in models of T1D.
An insulin signaling feedback loop regulates pancreas progenitor cell differentiation during islet development and regeneration
(Elsevier, 2016-01-15) Ye, Lihua; Robertson, Morgan A.; Mastracci, Teresa L.; Anderson, Ryan M.; Department of Pediatrics, IU School of Medicine
As one of the key nutrient sensors, insulin signaling plays an important role in integrating environmental energy cues with organism growth. In adult organisms, relative insufficiency of insulin signaling induces compensatory expansion of insulin-secreting pancreatic beta (β) cells. However, little is known about how insulin signaling feedback might influence neogenesis of β cells during embryonic development. Using genetic approaches and a unique cell transplantation system in developing zebrafish, we have uncovered a novel role for insulin signaling in the negative regulation of pancreatic progenitor cell differentiation. Blocking insulin signaling in the pancreatic progenitors hastened the expression of the essential β cell genes insulin and pdx1, and promoted β cell fate at the expense of alpha cell fate. In addition, loss of insulin signaling promoted β cell regeneration and destabilization of alpha cell character. These data indicate that insulin signaling constitutes a tunable mechanism for β cell compensatory plasticity during early development. Moreover, using a novel blastomere-to-larva transplantation strategy, we found that loss of insulin signaling in endoderm-committed blastomeres drove their differentiation into β cells. Furthermore, the extent of this differentiation was dependent on the function of the β cell mass in the host. Altogether, our results indicate that modulation of insulin signaling will be crucial for the development of β cell restoration therapies for diabetics; further clarification of the mechanisms of insulin signaling in β cell progenitors will reveal therapeutic targets for both in vivo and in vitro β cell generation.
Molecular Mechanisms of Nonalcoholic Fatty Liver Disease: Potential Role for 12-Lipoxygenase
(Elsevier, 2017) Samala, Niharika; Tersey, Sarah A.; Chalasani, Naga; Anderson, Ryan M.; Mirmira, Raghavendra G.; Department of Biochemistry and Molecular Biology, School of Medicine
Nonalcoholic fatty liver disease (NAFLD) is a spectrum of pathologies associated with fat accumulation in the liver. NAFLD is the most common cause of liver disease in the United States, affecting up to a third of the general population. It is commonly associated with features of metabolic syndrome, particularly insulin resistance. NAFLD shares the basic pathogenic mechanisms with obesity and insulin resistance, such as mitochondrial, oxidative and endoplasmic reticulum stress. Lipoxygenases catalyze the conversion of poly-unsaturated fatty acids in the plasma membrane—mainly arachidonic acid and linoleic acid—to produce oxidized pro-inflammatory lipid intermediates. 12-Lipoxygenase (12-LOX) has been studied extensively in setting of inflammation and insulin resistance. As insulin resistance is closely associated with development of NAFLD, the role of 12-LOX in pathogenesis of NAFLD has received increasing attention in recent years. In this review we discuss the role of 12-LOX in NAFLD pathogenesis and its potential role in emerging new therapeutics.

Browsing by Author "Anderson, Ryan M."

Results Per Page

Sort Options