Browsing by Author "Sinam, Ibotombi Singh"

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    Enhanced Ca2+-channeling complex formation at the ER-mitochondria interface underlies the pathogenesis of alcohol-associated liver disease
    (Springer Nature, 2023-03-27) Thoudam, Themis; Chanda, Dipanjan; Lee, Jung Yi; Jung, Min-Kyo; Sinam, Ibotombi Singh; Kim, Byung-Gyu; Park, Bo-Yoon; Kwon, Woong Hee; Kim, Hyo-Jeong; Kim, Myeongjin; Lim, Chae Won; Lee, Hoyul; Huh, Yang Hoon; Miller, Caroline A.; Saxena, Romil; Skill, Nicholas J.; Huda, Nazmul; Kusumanchi, Praveen; Ma, Jing; Yang, Zhihong; Kim, Min-Ji; Mun, Ji Young; Harris, Robert A.; Jeon, Jae-Han; Liangpunsakul, Suthat; Lee, In-Kyu; Pathology and Laboratory Medicine, School of Medicine
    Ca2+ overload-induced mitochondrial dysfunction is considered as a major contributing factor in the pathogenesis of alcohol-associated liver disease (ALD). However, the initiating factors that drive mitochondrial Ca2+ accumulation in ALD remain elusive. Here, we demonstrate that an aberrant increase in hepatic GRP75-mediated mitochondria-associated ER membrane (MAM) Ca2+-channeling (MCC) complex formation promotes mitochondrial dysfunction in vitro and in male mouse model of ALD. Unbiased transcriptomic analysis reveals PDK4 as a prominently inducible MAM kinase in ALD. Analysis of human ALD cohorts further corroborate these findings. Additional mass spectrometry analysis unveils GRP75 as a downstream phosphorylation target of PDK4. Conversely, non-phosphorylatable GRP75 mutation or genetic ablation of PDK4 prevents alcohol-induced MCC complex formation and subsequent mitochondrial Ca2+ accumulation and dysfunction. Finally, ectopic induction of MAM formation reverses the protective effect of PDK4 deficiency in alcohol-induced liver injury. Together, our study defines a mediatory role of PDK4 in promoting mitochondrial dysfunction in ALD.
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    Noncanonical PDK4 action alters mitochondrial dynamics to affect the cellular respiratory status
    (National Academy of Science, 2022) Thoudam, Themis; Chanda, Dipanjan; Sinam, Ibotombi Singh; Kim, Byung-Gyu; Kim, Mi-Jin; Oh, Chang Joo; Lee, Jung Yi; Kim, Min-Ji; Park, Soo Yeun; Lee, Shin Yup; Jung, Min-Kyo; Mun, Ji Young; Harris, Robert A.; Ishihara, Naotada; Jeon, Jae-Han; Lee, In-Kyu; Biochemistry and Molecular Biology, School of Medicine
    Dynamic regulation of mitochondrial morphology provides cells with the flexibility required to adapt and respond to electron transport chain (ETC) toxins and mitochondrial DNA-linked disease mutations, yet the mechanisms underpinning the regulation of mitochondrial dynamics machinery by these stimuli is poorly understood. Here, we show that pyruvate dehydrogenase kinase 4 (PDK4) is genetically required for cells to undergo rapid mitochondrial fragmentation when challenged with ETC toxins. Moreover, PDK4 overexpression was sufficient to promote mitochondrial fission even in the absence of mitochondrial stress. Importantly, we observed that the PDK4-mediated regulation of mitochondrial fission was independent of its canonical function, i.e., inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Phosphoproteomic screen for PDK4 substrates, followed by nonphosphorylatable and phosphomimetic mutations of the PDK4 site revealed cytoplasmic GTPase, Septin 2 (SEPT2), as the key effector molecule that acts as a receptor for DRP1 in the outer mitochondrial membrane to promote mitochondrial fission. Conversely, inhibition of the PDK4-SEPT2 axis could restore the balance in mitochondrial dynamics and reinvigorates cellular respiration in mitochondrial fusion factor, mitofusin 2-deficient cells. Furthermore, PDK4-mediated mitochondrial reshaping limits mitochondrial bioenergetics and supports cancer cell growth. Our results identify the PDK4-SEPT2-DRP1 axis as a regulator of mitochondrial function at the interface between cellular bioenergetics and mitochondrial dynamics.
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    Upregulation of the ERRγ–VDAC1 axis underlies the molecular pathogenesis of pancreatitis
    (National Academy of Science, 2023) Chanda, Dipanjan; Thoudam, Themis; Sinam, Ibotombi Singh; Lim, Chae Won; Kim, Myeongjin; Wang, Jiale; Lee, Kyeong-Min; Ma, Jing; Saxena, Romil; Choi, Jinhyuk; Oh, Chang Joo; Lee, Hoyul; Jeon, Yong Hyun; Cho, Sung Jin; Jung, Hoe-Yune; Park, Keun-Gyu; Choi, Hueng-Sik; Suh, Jae Myoung; Auwerx, Johan; Ji, Baoan; Liangpunsakul, Suthat; Jeon, Jae-Han; Lee, In-Kyu; Medicine, School of Medicine
    Emerging evidence suggest that transcription factors play multiple roles in the development of pancreatitis, a necroinflammatory condition lacking specific therapy. Estrogen-related receptor γ (ERRγ), a pleiotropic transcription factor, has been reported to play a vital role in pancreatic acinar cell (PAC) homeostasis. However, the role of ERRγ in PAC dysfunction remains hitherto unknown. Here, we demonstrated in both mice models and human cohorts that pancreatitis is associated with an increase in ERRγ gene expression via activation of STAT3. Acinar-specific ERRγ haploinsufficiency or pharmacological inhibition of ERRγ significantly impaired the progression of pancreatitis both in vitro and in vivo. Using systematic transcriptomic analysis, we identified that voltage-dependent anion channel 1 (VDAC1) acts as a molecular mediator of ERRγ. Mechanistically, we showed that induction of ERRγ in cultured acinar cells and mouse pancreata enhanced VDAC1 expression by directly binding to specific site of the Vdac1 gene promoter and resulted in VDAC1 oligomerization. Notably, VDAC1, whose expression and oligomerization were dependent on ERRγ, modulates mitochondrial Ca2+ and ROS levels. Inhibition of the ERRγ-VDAC1 axis could alleviate mitochondrial Ca2+ accumulation, ROS formation and inhibit progression of pancreatitis. Using two different mouse models of pancreatitis, we showed that pharmacological blockade of ERRγ-VDAC1 pathway has therapeutic benefits in mitigating progression of pancreatitis. Likewise, using PRSS1R122H-Tg mice to mimic human hereditary pancreatitis, we demonstrated that ERRγ inhibitor also alleviated pancreatitis. Our findings highlight the importance of ERRγ in pancreatitis progression and suggests its therapeutic intervention for prevention and treatment of pancreatitis.