Browsing by Author "Muralidharan, Pooja"

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    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.
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    Effect of Curcuminoids in Turmeric on Developing Zebrafish Treated with Ethanol
    (Office of the Vice Chancellor for Research, 2016-04-08) Connors, Craig; Mohammed, Arooj; Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James; Marrs, Kathleen A.; Chism, Grady
    This experiment was designed with the intention of determining whether turmeric could act as a rescue agent to prevent or mitigate the extent of Fetal Alcohol Spectrum Disorder (FASD) caused by early ethanol exposure using zebrafish as a model system. A range of turmeric concentrations were made from a stock solution of turmeric dissolved in ethanol (1mg turmeric in 5mL ethanol). The active agents in turmeric are the curcuminoids: Curcumin, Desmethoxycurcumin, and Bisdemethoxycurcumin. The curcuminoids concentration was estimated using liquid chromatography. These agents were present in the turmeric stock solution at the following concentrations: Bisdemethoxycurcumin: 36.6 +/- 0.1 ug/mL, Desmethoxycurcumin: 43.4 +/- 0.1 ug/mL, and Curcumin: 124.1 +/- 0.2 ug/mL. Untreated zebrafish embryos were placed in embryo medium, ethanol treated embryos in 100mM ethanol containing embryo medium, and turmeric co-supplemented medium with differing concentrations of turmeric. Since the turmeric stock solution was dissolved in ethanol, the concentration of ethanol was kept at a constant 100mM ethanol and the amount of turmeric solution added. The concentrations of the test plates were then based on this solution and made to be 100 mM ethanol and 1.16 uM curcuminoids, 100 mM ethanol and 1.74 uM curcuminoids, and 100 mM ethanol and 2.32 uM curcuminoids. The developing embryos were treated with the turmeric solution and/or ethanol during 2-24 hours post fertilization (hpf). These embryos were imaged at 72 hpf and their body length and eye diameter were measured. The embryos supplemented with curcuminoids showed a significant rescue effect on the body length and eye diameter compared to ethanol treated embryos. This indicates that the curcuminoids acted as a rescue agent to reduce the effects that are typical of FASD in developing zebrafish.
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    Embryonic Ethanol Exposure Dysregulates BMP and Notch Signaling, Leading to Persistent Atrio-Ventricular Valve Defects in Zebrafish
    (Plos, 2016-08-24) Sarmah, Swapnalee; Muralidharan, Pooja; Marrs, James A.; Department of Biology, School of Science
    Fetal alcohol spectrum disorder (FASD), birth defects associated with ethanol exposure in utero, includes a wide spectrum of congenital heart defects (CHDs), the most prevalent of which are septal and conotruncal defects. Zebrafish FASD model was used to dissect the mechanisms underlying FASD-associated CHDs. Embryonic ethanol exposure (3–24 hours post fertilization) led to defects in atrio-ventricular (AV) valvulogenesis beginning around 37 hpf, a morphogenetic event that arises long after ethanol withdrawal. Valve leaflets of the control embryos comprised two layers of cells confined at the compact atrio-ventricular canal (AVC). Ethanol treated embryos had extended AVC and valve forming cells were found either as rows of cells spanning the AVC or as unorganized clusters near the AV boundary. Ethanol exposure reduced valve precursors at the AVC, but some ventricular cells in ethanol treated embryos exhibited few characteristics of valve precursors. Late staged larvae and juvenile fish exposed to ethanol during embryonic development had faulty AV valves. Examination of AVC morphogenesis regulatory networks revealed that early ethanol exposure disrupted the Bmp signaling gradient in the heart during valve formation. Bmp signaling was prominent at the AVC in controls, but ethanol-exposed embryos displayed active Bmp signaling throughout the ventricle. Ethanol exposure also led to mislocalization of Notch signaling cells in endocardium during AV valve formation. Normally, highly active Notch signaling cells were organized at the AVC. In ethanol-exposed embryos, highly active Notch signaling cells were dispersed throughout the ventricle. At later stages, ethanol-exposed embryos exhibited reduced Wnt/β-catenin activity at the AVC. We conclude that early embryonic ethanol exposure alters Bmp, Notch and other signaling activities during AVC differentiation leading to faulty valve morphogenesis and valve defects persist in juvenile fish.
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    Ethanol-induced Retinal Defects are Rescued by Retinoic Acid Supplement in Developing Zebrafish Embryos
    (Office of the Vice Chancellor for Research, 2013-04-05) Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James A.
    Fetal Alcohol Spectrum Disorder (FASD) is caused by prenatal alcohol exposure, producing a spectrum of defects including facial abnormalities, sensory (visual and auditory) deficits, impaired fine motor skills and learning deficits including mental retardation. Our laboratory has used a zebrafish model for FASD that exposes embryos to ethanol during early development (midblastula transition through somitogenesis). Children diagnosed with FASD frequently show severe eye defects ranging from small eyes, underdeveloped optic nerve, and cataract. Zebrafish embryos exposed to ethanol showed defects similar to human eye birth defects. Presence of ethanol affected the differentiation of many retinal cell types including, retinal ganglion cells and photoreceptors. We hypothesize that ethanol may affect retinal patterning by competing with Retinaldehyde dehydrogenase (Raldh), reducing retinoic acid (RA) synthesis and signaling. Co-treatment of embryos with ethanol and 10-9 M RA could rescue the photoreceptor and retinal ganglion cell differentiation defects in the retina. RA plays a crucial role in the dorso-ventral patterning of the retina, and the enzymes involved in RA biosynthesis are expressed in the ventral retina during mid-somitogenesis stage. Our experiments showed that ethanol exposure during that critical time window when Raldh is expressed in the ventral retina causes severe defects in retinal cell specification. No defects were induced by ethanol exposure at the earlier stages. Presence of RA during photoreceptor differentiation could rescue ethanol-induced photoreceptor differentiation defects. Future work will dissect molecular mechanisms underlying ethanol defects, including retinoic acid-mediated eye development mechanisms. Determining the effects of ethanol exposure on retinal morphogenesis and differentiation will help identify potential therapeutic targets for ocular defects in this regrettably frequent birth defect syndrome.
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    Fetal Alcohol Spectrum Disorder (FASD) Associated Neural Defects: Complex Mechanisms and Potential Therapeutic Targets
    (MDPI, 2013-06-19) Muralidharan, Pooja; Sarmah, Swapnalee; Zhou, Feng C.; Marrs, James A.; Biology, School of Science
    Fetal alcohol spectrum disorder (FASD), caused by prenatal alcohol exposure, can result in craniofacial dysmorphism, cognitive impairment, sensory and motor disabilities among other defects. FASD incidences are as high as 2% to 5 % children born in the US, and prevalence is higher in low socioeconomic populations. Despite various mechanisms being proposed to explain the etiology of FASD, the molecular targets of ethanol toxicity during development are unknown. Proposed mechanisms include cell death, cell signaling defects and gene expression changes. More recently, the involvement of several other molecular pathways was explored, including non-coding RNA, epigenetic changes and specific vitamin deficiencies. These various pathways may interact, producing a wide spectrum of consequences. Detailed understanding of these various pathways and their interactions will facilitate the therapeutic target identification, leading to new clinical intervention, which may reduce the incidence and severity of these highly prevalent preventable birth defects. This review discusses manifestations of alcohol exposure on the developing central nervous system, including the neural crest cells and sensory neural placodes, focusing on molecular neurodevelopmental pathways as possible therapeutic targets for prevention or protection.
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    Retinal Wnt signaling defect in a zebrafish fetal alcohol spectrum disorder model
    (PLOS, 2018-08-01) Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James A.; Biology, School of Science
    Fetal alcohol spectrum disorder caused by prenatal alcohol exposure includes ocular abnormalities (microphthalmia, photoreceptor dysfunction, cataracts). Zebrafish embryos exposed to ethanol from gastrulation through somitogenesis show severe ocular defects, including microphthalmia and photoreceptor differentiation defects. Ethanol-treated zebrafish had an enlarged ciliary marginal zone (CMZ) relative to the retina size and reduced Müller glial cells (MGCs). Ethanol exposure produced immature photoreceptors with increased proliferation, indicating cell cycle exit failure. Signaling mechanisms in the CMZ were affected by embryonic ethanol exposure, including Wnt signaling in the CMZ, Notch signaling and neurod gene expression. Retinoic acid or folic acid co-supplementation with ethanol rescued Wnt signaling and retinal differentiation. Activating Wnt signaling using GSK3 inhibitor (LSN 2105786; Eli Lilly and Co.) restored retinal cell differentiation pathways. Ethanol exposed embryos were treated with Wnt agonist, which rescued Wnt-active cells in the CMZ, Notch-active cells in the retina, proliferation, and photoreceptor terminal differentiation. Our results illustrate the critical role of Wnt signaling in ethanol-induced retinal defects.
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    Retinal Wnt signaling defect in a zebrafish fetal alcohol spectrum disorder model
    (PLOS, 2018-08-01) Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James A.; Biology, School of Science
    Fetal alcohol spectrum disorder caused by prenatal alcohol exposure includes ocular abnormalities (microphthalmia, photoreceptor dysfunction, cataracts). Zebrafish embryos exposed to ethanol from gastrulation through somitogenesis show severe ocular defects, including microphthalmia and photoreceptor differentiation defects. Ethanol-treated zebrafish had an enlarged ciliary marginal zone (CMZ) relative to the retina size and reduced Müller glial cells (MGCs). Ethanol exposure produced immature photoreceptors with increased proliferation, indicating cell cycle exit failure. Signaling mechanisms in the CMZ were affected by embryonic ethanol exposure, including Wnt signaling in the CMZ, Notch signaling and neurod gene expression. Retinoic acid or folic acid co-supplementation with ethanol rescued Wnt signaling and retinal differentiation. Activating Wnt signaling using GSK3 inhibitor (LSN 2105786; Eli Lilly and Co.) restored retinal cell differentiation pathways. Ethanol exposed embryos were treated with Wnt agonist, which rescued Wnt-active cells in the CMZ, Notch-active cells in the retina, proliferation, and photoreceptor terminal differentiation. Our results illustrate the critical role of Wnt signaling in ethanol-induced retinal defects.
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    Turmeric Extract Rescues Ethanol‐Induced Developmental Defect in the Zebrafish Model for Fetal Alcohol Spectrum Disorder (FASD)
    (Wiley, 2017) Muralidharan, Pooja; Connors, Craig; Mohammed, Arooj S.; Sarmah, Swapnalee; Marrs, Kathleen A.; Marrs, James A.; Chism, Grady W.; Biology, School of Science
    Prenatal ethanol exposure causes the most frequent preventable birth disorder, fetal alcohol spectrum disorder (FASD). The effect of turmeric extracts in rescuing an ethanol‐induced developmental defect using zebrafish as a model was determined. Ethanol‐induced oxidative stress is one of the major mechanisms underlying FASD. We hypothesize that antioxidant inducing properties of turmeric may alleviate ethanol‐induced defects. Curcuminoid content of the turmeric powder extract (5 mg/mL turmeric in ethanol) was determined by UPLC and found to contain Curcumin (124.1 ± 0.2 μg/mL), Desmethoxycurcumin (43.4 ± 0.1 μg/mL), and Bisdemethoxycurcumin (36.6 ± 0.1 μg/mL). Zebrafish embryos were treated with 100 mM (0.6% v/v) ethanol during gastrulation through organogenesis (2 to 48 h postfertilization (hpf)) and supplemented with turmeric extract to obtain total curcuminoid concentrations of 0, 1.16, 1.72, or 2.32 μM. Turmeric supplementation showed significant rescue of the body length at 72 hpf compared to ethanol‐treated embryos. The mechanism underlying the rescue remains to be determined.
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    Using Zebrafish to Implement a Course-Based Undergraduate Research Experience to Study Teratogenesis in Two Biology Laboratory Courses
    (Mary Ann Liebert, 2016-08) Sarmah, Swapnalee; Chism, Grady W., III; Vaughan, Martin A.; Muralidharan, Pooja; Marrs, Jim A.; Marrs, Kathleen A.; Biology, School of Science
    A course-based undergraduate research experience (CURE) spanning three semesters was introduced into freshman and sophomore biology classes, with the hypothesis that participation in a CURE affects skills in research, communication, and collaboration, which may help students persist in science. Student research projects were centered on the hypothesis that nicotine and caffeine exposure during early development affects gastrulation and heart development in zebrafish. First, freshmen generated original data showing distinct effects of embryonic nicotine and caffeine exposure on zebrafish heart development and function. Next, Cell Biology laboratory students continued the CURE studies and identified novel teratogenic effects of nicotine and caffeine during gastrulation. Finally, new freshmen continued the CURE research, examining additional toxicant effects on development. Students designed new protocols, made measurements, presented results, and generated high-quality preliminary data that were studied in successive semesters. By implementing this project, the CURE extended faculty research and provided a scalable model to address national goals to involve more undergraduates in authentic scientific research. In addition, student survey results support the hypothesis that CUREs provide significant gains in student ability to (1) design experiments, (2) analyze data, and (3) make scientific presentations, translating into high student satisfaction and enhanced learning.
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    Zebrafish retinal stem cell differentiation mechanisms are disrupted by embryonic ethanol exposure
    (Office of the Vice Chancellor for Research, 2016-04-08) Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James A.
    Prenatal alcohol exposure can lead to a wide range of developmental abnormalities, which are included under the umbrella term fetal alcohol spectrum disorder (FASD). To understand the genesis of FASD defects, the zebrafish is important mechanistic animal model, particularly for retinal development. Previous work from our laboratory showed that ethanol treatment during gastrulation through somitogenesis in zebrafish embryos could recapitulate human ocular defects including microphthalmia, optic nerve hypoplasia, and photoreceptor defects. Ethanol-treated embryos showed increased retinal proliferation in the outer nuclear layer (ONL), inner nuclear layer (INL), and ciliary marginal zone (CMZ). Retinoic acid (RA) and folic acid (FA) co-supplementation rescued most ethanol-induced retinal defects, suggesting that nutrient deficiencies contribute to FASD. To better understand the genesis of ethanol-induced retinal cell differentiation defects, effects of ethanol exposure on retinal stem cell populations in the CMZ and Müller glial cell populations were examined. Ethanol treated retinas had an expanded CMZ, and a reduced expression domain for the cell cycle exit marker, cdkn1c. Ethanol treated retinas also showed reduced GFAP-positive Müller glial cells, which are a stem cell population in the central retina. At 72 hpf, the ONL of ethanol exposed fish showed few photoreceptors expressing terminal differentiation markers. Importantly, these poorly differentiated photoreceptors co-expressed the bHLH 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 disruption due to ethanol exposure. Ethanol exposure severely disrupted Wnt and Notch signaling, which are critical for stem cell behavior and differentiation. These defects were rescued by Wnt signaling agonist, RA, and FA treatments. These results suggest ethanol disrupted retinal cell differentiation mechanisms. Further analysis of underlying molecular mechanisms will provide insight into the ethanol-induced retinal defects and potential therapeutic targets.