Browsing by Author "Graham, Brett"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Characterization of a Novel Fis1 Interactor Required for Peripheral Distribution of the Mitochondrion of Toxoplasma Gondii
    (2021-02) Jacobs, Kylie; Arrizabalaga, Gustavo; Gilk, Stacey; Graham, Brett; John, Chandy; Yang, Frank
    Toxoplasma’s singular mitochondrion is extremely dynamic and undergoes morphological changes throughout the parasite’s life cycle. While intracellular‚ the mitochondrion is maintained in a lasso shape that stretches around the parasite periphery and is in close proximity to the pellicle‚ suggesting the presence of membrane contact sites. Upon egress‚ these contact sites disappear‚ and the mitochondrion retracts and collapses towards the apical end of the parasite. Once reinvaded‚ the lasso shape is quickly reformed‚ indicating that dynamic membrane contact sites regulate the positioning of the mitochondrion. We discovered a novel protein (TgGT1_265180) that associates with the mitochondrion via interactions with the fission related protein Fis1. Knockout of TgGT1_265180‚ which we have dubbed LMF1 for Lasso Maintenance Factor 1‚ results in a complete disruption of the normal mitochondrial morphology. In intracellular LMF1 knockout parasites, the mitochondrial lasso shape is disrupted‚ and instead it is collapsed as normally only seen in extracellular parasites. Additionally, proper mitochondrial segregation is disrupted‚ resulting in parasites with no mitochondrion and extra mitochondrial material outside of the parasites. These gross morphological changes are associated with a significant reduction of parasite propagation and can be rescued by reintroduction of a wildtype copy of LMF1. Co-immunoprecipitations and Yeast Two-Hybrid predict interactions with the parasite pellicle. Therefore, we hypothesize that LMF1 mediates contact between the mitochondrion and the pellicle in a regulatable fashion‚ and that the LMF1-dependent morphodynamics are critical for parasite propagation. Current studies are focused on characterizing the consequences of mitochondrial collapse and identifying proteins that interact with LMF1 to position the mitochondrion to the periphery of the parasite.
  • Thumbnail Image
    Item
    Correction to: De novo and inherited TCF20 pathogenic variants are associated with intellectual disability, dysmorphic features, hypotonia, and neurological impairments with similarities to Smith-Magenis syndrome
    (Biomed Central, 2019-03-25) Vetrini, Francesco; McKee, Shane; Rosenfeld, Jill A.; Suri, Mohnish; Lewis, Andrea M.; Nugent, Kimberly Margaret; Roeder, Elizabeth; Littlejohn, Rebecca O.; Holder, Sue; Zhu, Wenmiao; Alaimo, Joseph T.; Graham, Brett; Harris, Jill M.; Gibson, James B.; Pastore, Matthew; McBride, Kim L.; Komara, Makanko; Al-Gazali, Lihadh; Al Shamsi, Aisha; Fanning, Elizabeth A.; Wierenga, Klaas J.; Scott, Daryl A.; Ben-Neriah, Ziva; Meiner, Vardiella; Cassuto, Hanoch; Elpeleg, Orly; Lloyd Holder Jr, J.; Burrage, Lindsay C.; Seaver, Laurie H.; Van Maldergem, Lionel; Mahida, Sonal; Soul, Janet S.; Marlatt, Margaret; Matyakhina, Ludmila; Vogt, Julie; Gold, June-Anne; Park, Soo-Mi; Varghese, Vinod; Lampe, Anne K.; Kumar, Ajith; Lees, Melissa; Holder-Espinasse, Muriel; McConnell, Vivienne; Bernhard, Birgitta; Blair, Ed; Harrison, Victoria; Muzny, Donna M.; Gibbs, Richard A.; Elsea, Sarah H.; Posey, Jennifer E.; Bi, Weimin; Lalani, Seema; Xia, Fan; Yang, Yaping; Eng, Christine M.; Lupski, James R.; Liu, Pengfei; Medical and Molecular Genetics, School of Medicine
    It was highlighted that the original article [1] contained a typographical error in the Results section. Subject 17 was incorrectly cited as Subject 1. This Correction article shows the revised statement. The original article has been updated.
  • Thumbnail Image
    Item
    Human Stem Cell Differentiated Retinal Ganglion Cells for Developing Glaucoma Neuroprotection and Cell Replacement Strategies
    (2024-07) Anbarasu, Kavitha; Das, Arupratan; Corson, Timothy; Meyer, Jason; Graham, Brett; Janga, Sarath
    Progressive loss of retinal ganglion cells (RGCs) leads to glaucoma. Early diagnosis offers an opportunity to protect existing RGCs. In advanced glaucoma, most RGCs are lost causing blindness and cell replacement therapy the only option. We used a human stem cell-based RGC differentiation model to develop neuroprotection by restoring mitochondrial homeostasis and enhancing RGC differentiation efficiency to increase the success of cell replacement therapy. Unmyelinated axons in RGCs require high levels of ATP, making disrupted mitochondria a risk factor in glaucoma. Our goal was to restore mitochondrial homeostasis through mitophagy (mitochondrial autophagy) and mitobiogenesis (mitochondrial biogenesis). Mutations in the mitophagy protein Optineurin (OPTNE50K) are found in patients with normal tension glaucoma and hence, we also used RGCs with the E50K mutation. We discovered that hRGCE50Ks suffer from mitobiogenesis issues, Parkin/Pink mediated mitophagy defects, and have OPTNE50K-Tank binding kinase-1 (TBK1) aggregates. hRGCE50Ks have lower mitochondrial mass and a higher mitochondrial load. We inhibited TBK1 to induce mitochondrial biogenesis and dissolve OPTNE50K-TBK1 aggregates. Our results show TBK1 inhibition triggered mitobiogenesis, dissolved aggregates, decreased mitochondrial ATP production load, and increased spare respiratory capacity, leading to neuroprotection. With complete RGC loss, enhancing differentiation to progenitor cells with lower cell division capacity can improve the success of cell replacement therapy and reduce teratoma formation and poor tissue integration. We observed that stem cells use proteasomes for mitochondrial degradation, while hRGCs use the lysosomal mitophagy pathway. Our results indicate that proteasomal activity declines during differentiation to hRGCs. Inhibition of proteasomal activity during early differentiation resulted in higher and faster RGC differentiation, with similar effects seen in motor neuron differentiation. We did not observe metabolic reprogramming in differentiating cells upon proteasomal activity inhibition but saw changes in cell cycle distribution, specifically an increase in the number of cells in the G1 phase. Proteomics analysis post-inhibitory treatment showed elevated neuronal differentiation proteins. Our results can be translated to minimize injection cell numbers and other risks of cell replacement therapy. In summary, my research identifies novel mechanisms for restoring mitochondrial homeostasis for neuroprotection in glaucomatous RGCs and develops an enhanced differentiation strategy to aid the success of cell replacement therapy.
  • Thumbnail Image
    Item
    De novo and inherited TCF20 pathogenic variants are associated with intellectual disability, dysmorphic features, hypotonia, and neurological impairments with similarities to Smith-Magenis syndrome
    (BMC, 2019-02-28) Vetrini, Francesco; McKee, Shane; Rosenfeld, Jill A.; Suri, Mohnish; Lewis, Andrea M.; Nugent, Kimberly Margaret; Roeder, Elizabeth; Littlejohn, Rebecca O.; Holder, Sue; Zhu, Wenmiao; Alaimo, Joseph T.; Graham, Brett; Harris, Jill M.; Gibson, James B.; Pastore, Matthew; McBride, Kim L.; Komara, Makanko; Al-Gazali, Lihadh; Al Shamsi, Aisha; Fanning, Elizabeth A.; Wierenga, Klaas J.; Scott, Daryl A.; Ben-Neriah, Ziva; Meiner, Vardiella; Cassuto, Hanoch; Elpeleg, Orly; Holder, J. Lloyd, Jr.; Burrage, Lindsay C.; Seaver, Laurie H.; Van Maldergem, Lionel; Mahida, Sonal; Soul, Janet S.; Marlatt, Margaret; Matyakhina, Ludmila; Vogt, Julie; Gold, June-Anne; Park, Soo-Mi; Varghese, Vinod; Lampe, Anne K.; Kumar, Ajith; Lees, Melissa; Holder-Espinasse, Muriel; McConnell, Vivienne; Bernhard, Birgitta; Blair, Ed; Harrison, Victoria; The DDD study; Muzny, Donna M.; Gibbs, Richard A.; Elsea, Sarah H.; Posey, Jennifer E.; Bi, Weimin; Lalani, Seema; Xia, Fan; Yang, Yaping; Eng, Christine M.; Lupski, James R.; Liu, Pengfei; Medical and Molecular Genetics, School of Medicine
    BACKGROUND: Neurodevelopmental disorders are genetically and phenotypically heterogeneous encompassing developmental delay (DD), intellectual disability (ID), autism spectrum disorders (ASDs), structural brain abnormalities, and neurological manifestations with variants in a large number of genes (hundreds) associated. To date, a few de novo mutations potentially disrupting TCF20 function in patients with ID, ASD, and hypotonia have been reported. TCF20 encodes a transcriptional co-regulator structurally related to RAI1, the dosage-sensitive gene responsible for Smith-Magenis syndrome (deletion/haploinsufficiency) and Potocki-Lupski syndrome (duplication/triplosensitivity). METHODS: Genome-wide analyses by exome sequencing (ES) and chromosomal microarray analysis (CMA) identified individuals with heterozygous, likely damaging, loss-of-function alleles in TCF20. We implemented further molecular and clinical analyses to determine the inheritance of the pathogenic variant alleles and studied the spectrum of phenotypes. RESULTS: We report 25 unique inactivating single nucleotide variants/indels (1 missense, 1 canonical splice-site variant, 18 frameshift, and 5 nonsense) and 4 deletions of TCF20. The pathogenic variants were detected in 32 patients and 4 affected parents from 31 unrelated families. Among cases with available parental samples, the variants were de novo in 20 instances and inherited from 4 symptomatic parents in 5, including in one set of monozygotic twins. Two pathogenic loss-of-function variants were recurrent in unrelated families. Patients presented with a phenotype characterized by developmental delay, intellectual disability, hypotonia, variable dysmorphic features, movement disorders, and sleep disturbances. CONCLUSIONS: TCF20 pathogenic variants are associated with a novel syndrome manifesting clinical characteristics similar to those observed in Smith-Magenis syndrome. Together with previously described cases, the clinical entity of TCF20-associated neurodevelopmental disorders (TAND) emerges from a genotype-driven perspective.