IU Indianapolis ScholarWorks :: Browsing by Subject "Cell Biology"

Browsing by Subject "Cell Biology"

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Claudin-2 deficiency associates with hypercalciuria in mice and human kidney stone disease
(American Society for Clinical Investigation, 2020-03-09) Curry, Joshua N.; Saurette, Matthew; Askari, Masomeh; Pei, Lei; Filla, Michael B.; Beggs, Megan R.; Rowe, Peter S. N.; Fields, Timothy; Sommer, Andre J.; Tanikawa, Chizu; Kamatani, Yoichiro; Evan, Andrew P.; Totonchi, Mehdi; Alexander, R. Todd; Matsuda, Koichi; Yu, Alan S. L.; Anatomy and Cell Biology, School of Medicine
The major risk factor for kidney stone disease is idiopathic hypercalciuria. Recent evidence implicates a role for defective calcium reabsorption in the renal proximal tubule. We hypothesized that claudin-2, a paracellular cation channel protein, mediates proximal tubule calcium reabsorption. We found that claudin-2–null mice have hypercalciuria due to a primary defect in renal tubule calcium transport and papillary nephrocalcinosis that resembles the intratubular plugs in kidney stone formers. Our findings suggest that a proximal tubule defect in calcium reabsorption predisposes to papillary calcification, providing support for the vas washdown hypothesis. Claudin-2–null mice were also found to have increased net intestinal calcium absorption, but reduced paracellular calcium permeability in the colon, suggesting that this was due to reduced intestinal calcium secretion. Common genetic variants in the claudin-2 gene were associated with decreased tissue expression of claudin-2 and increased risk of kidney stones in 2 large population-based studies. Finally, we describe a family in which males with a rare missense variant in claudin-2 have marked hypercalciuria and kidney stone disease. Our findings indicate that claudin-2 is a key regulator of calcium excretion and a potential target for therapies to prevent kidney stones.
Conditional Myh9 and Myh10 inactivation in adult mouse renal epithelium results in progressive kidney disease
(American Society for Clinical Investigation, 2020-11-05) Otterpohl, Karla L.; Busselman, Brook W.; Ratnayake, Ishara; Hart, Ryan G.; Hart, Kimberly R.; Evans, Claire M.; Phillips, Carrie L.; Beach, Jordan R.; Ahrenkiel, Phil; Molitoris, Bruce A.; Surendran, Kameswaran; Chandrasekar, Indra; Pathology and Laboratory Medicine, School of Medicine
Actin-associated nonmuscle myosin II (NM2) motor proteins play critical roles in a myriad of cellular functions, including endocytosis and organelle transport pathways. Cell type–specific expression and unique subcellular localization of the NM2 proteins, encoded by the Myh9 and Myh10 genes, in the mouse kidney tubules led us to hypothesize that these proteins have specialized functional roles within the renal epithelium. Inducible conditional knockout (cKO) of Myh9 and Myh10 in the renal tubules of adult mice resulted in progressive kidney disease. Prior to overt renal tubular injury, we observed intracellular accumulation of the glycosylphosphatidylinositol-anchored protein uromodulin (UMOD) and gradual loss of Na+ K+ 2Cl– cotransporter from the apical membrane of the thick ascending limb epithelia. The UMOD accumulation coincided with expansion of endoplasmic reticulum (ER) tubules and activation of ER stress and unfolded protein response pathways in Myh9&10-cKO kidneys. We conclude that NM2 proteins are required for localization and transport of UMOD and loss of function results in accumulation of UMOD and ER stress–mediated progressive renal tubulointerstitial disease. These observations establish cell type–specific role(s) for NM2 proteins in regulation of specialized renal epithelial transport pathways and reveal the possibility that human kidney disease associated with MYH9 mutations could be of renal epithelial origin.
Enhancing excitatory activity of somatosensory cortex alleviates neuropathic pain through regulating homeostatic plasticity
(Nature Publishing group, 2017-10-06) Xiong, Wenhui; Ping, Xingjie; Ripsch, Matthew S.; Chavez, Grace Santa Cruz; Hannon, Heidi Elise; Jiang, Kewen; Bao, Chunhui; Jadhav, Vaishnavi; Chen, Lifang; Chai, Zhi; Ma, Cungen; Wu, Huangan; Feng, Jianqiao; Blesch, Armin; White, Fletcher A.; Jin, Xiaoming; Anatomy and Cell Biology, School of Medicine
Central sensitization and network hyperexcitability of the nociceptive system is a basic mechanism of neuropathic pain. We hypothesize that development of cortical hyperexcitability underlying neuropathic pain may involve homeostatic plasticity in response to lesion-induced somatosensory deprivation and activity loss, and can be controlled by enhancing cortical activity. In a mouse model of neuropathic pain, in vivo two-photon imaging and patch clamp recording showed initial loss and subsequent recovery and enhancement of spontaneous firings of somatosensory cortical pyramidal neurons. Unilateral optogenetic stimulation of cortical pyramidal neurons both prevented and reduced pain-like behavior as detected by bilateral mechanical hypersensitivity of hindlimbs, but corpus callosotomy eliminated the analgesic effect that was ipsilateral, but not contralateral, to optogenetic stimulation, suggesting involvement of inter-hemispheric excitatory drive in this effect. Enhancing activity by focally blocking cortical GABAergic inhibition had a similar relieving effect on the pain-like behavior. Patch clamp recordings from layer V pyramidal neurons showed that optogenetic stimulation normalized cortical hyperexcitability through changing neuronal membrane properties and reducing frequency of excitatory postsynaptic events. We conclude that development of neuropathic pain involves abnormal homeostatic activity regulation of somatosensory cortex, and that enhancing cortical excitatory activity may be a novel strategy for preventing and controlling neuropathic pain.
Formation of colorectal liver metastases induces musculoskeletal and metabolic abnormalities consistent with exacerbated cachexia
(American Society for Clinical Investigation, 2020-04-16) Huot, Joshua R.; Novinger, Leah J.; Pin, Fabrizio; Narasimhan, Ashok; Zimmers, Teresa A.; O’Connell, Thomas M.; Bonetto, Andrea; Surgery, School of Medicine
Advanced colorectal cancer (CRC) is often accompanied by development of liver metastases (LMs) and skeletal muscle wasting (i.e., cachexia). Despite plaguing the majority of CRC patients, cachexia remains unresolved. By using mice injected with Colon-26 mouse tumors, either subcutaneously (s.c.; C26) or intrasplenically to mimic hepatic dissemination of cancer cells (mC26), here we aimed to further characterize functional, molecular, and metabolic effects on skeletal muscle and examine whether LMs exacerbate CRC-induced cachexia. C26-derived LMs were associated with progressive loss of body weight, as well as with significant reductions in skeletal muscle size and strength, in line with reduced phosphorylation of markers of protein anabolism and enhanced protein catabolism. mC26 hosts showed prevalence of fibers with glycolytic metabolism and enhanced lipid accumulation, consistent with abnormalities of mitochondrial homeostasis and energy metabolism. In a comparison with mice bearing s.c. C26, cachexia appeared exacerbated in the mC26 hosts, as also supported by differentially expressed pathways within skeletal muscle. Overall, our model recapitulates the cachectic phenotype of metastatic CRC and reveals that formation of LMs resulting from CRC exacerbate cancer-induced skeletal muscle wasting by promoting differential gene expression signatures.
Heme Synthesis Inhibition Blocks Angiogenesis via Mitochondrial Dysfunction
(Elsevier, 2020-07-19) Shetty, Trupti; Sishtla, Kamakshi; Park, Bomina; Repass, Matthew J.; Corson, Timothy W.; Ophthalmology, School of Medicine
The relationship between heme metabolism and angiogenesis is poorly understood. The final synthesis of heme occurs in mitochondria, where ferrochelatase (FECH) inserts Fe2+ into protoporphyrin IX to produce proto-heme IX. We previously showed that FECH inhibition is antiangiogenic in human retinal microvascular endothelial cells (HRECs) and in animal models of ocular neovascularization. In the present study, we sought to understand the mechanism of how FECH and thus heme is involved in endothelial cell function. Mitochondria in endothelial cells had several defects in function after heme inhibition. FECH loss changed the shape and mass of mitochondria and led to significant oxidative stress. Oxidative phosphorylation and mitochondrial Complex IV were decreased in HRECs and in murine retina ex vivo after heme depletion. Supplementation with heme partially rescued phenotypes of FECH blockade. These findings provide an unexpected link between mitochondrial heme metabolism and angiogenesis.
The impact of telomeres and telomerase in cellular biology and medicine: it’s not the end of the story
(Wiley, 2011-01) Herbert, Brittney-Shea; Department of Medical & Molecular Genetics, IU School of Medicine
Lrp4 Mediates Bone Homeostasis and Mechanotransduction through Interaction with Sclerostin In Vivo
(Elsevier, 2019-10-25) Bullock, Whitney A.; Hoggatt, April M.; Horan, Daniel J.; Elmendorf, Andrew J.; Sato, Amy Y.; Bellido, Teresita; Loots, Gabriela G.; Pavalko, Fredrick M.; Robling, Alexander G.; Anatomy and Cell Biology, School of Medicine
Wnt signaling plays a key role in regulating bone remodeling. In vitro studies suggest that sclerostin's inhibitory action on Lrp5 is facilitated by the membrane-associated receptor Lrp4. We generated an Lrp4 R1170W knockin mouse model (Lrp4KI), based on a published mutation in patients with high bone mass (HBM). Lrp4KI mice have an HBM phenotype (assessed radiographically), including increased bone strength and formation. Overexpression of a Sost transgene had osteopenic effects in Lrp4-WT but not Lrp4KI mice. Conversely, sclerostin inhibition had blunted osteoanabolic effects in Lrp4KI mice. In a disuse-induced bone wasting model, Lrp4KI mice exhibit significantly less bone loss than wild-type (WT) mice. In summary, mice harboring the Lrp4-R1170W missense mutation recapitulate the human HBM phenotype, are less sensitive to altered sclerostin levels, and are protected from disuse-induced bone loss. Lrp4 is an attractive target for pharmacological targeting aimed at increasing bone mass and preventing bone loss due to disuse.
A Read/Write Mechanism Connects p300 Bromodomain Function to H2A.Z Acetylation
(Elsevier, 2019-11-22) Colino-Sanguino, Yolanda; Cornett, Evan M.; Moulder, David; Smith, Grady C.; Hrit, Joel; Cordeiro-Spinetti, Eric; Vaughan, Robert M.; Krajewski, Krzysztof; Rothbart, Scott B.; Clark, Susan J.; Valdés-Mora, Fátima; Biochemistry and Molecular Biology, School of Medicine
Acetylation of the histone variant H2A.Z (H2A.Zac) occurs at active regulatory regions associated with gene expression. Although the Tip60 complex is proposed to acetylate H2A.Z, functional studies suggest additional enzymes are involved. Here, we show that p300 acetylates H2A.Z at multiple lysines. In contrast, we found that although Tip60 does not efficiently acetylate H2A.Z in vitro, genetic inhibition of Tip60 reduces H2A.Zac in cells. Importantly, we found that interaction between the p300-bromodomain and H4 acetylation (H4ac) enhances p300-driven H2A.Zac. Indeed, H2A.Zac and H4ac show high genomic overlap, especially at active promoters. We also reveal unique chromatin features and transcriptional states at enhancers correlating with co-occurrence or exclusivity of H4ac and H2A.Zac. We propose that differential H4 and H2A.Z acetylation signatures can also define the enhancer state. In conclusion, we show both Tip60 and p300 contribute to H2A.Zac and reveal molecular mechanisms of writer/reader crosstalk between H2A.Z and H4 acetylation through p300.
Suppression of lysosome function induces autophagy via a feedback down-regulation of MTOR complex 1 (MTORC1) activity
(ASBMB, 2013-12-13) Li, Min; Khambu, Bilon; Zhang, Hao; Kang, Jeong-Han; Chen, Xiayun; Chen`, Daohong; Vollmer, Laura; Liu, Pei-Qing; Vogt, Andreas; Yin, Xiao-Ming; Department of Pathology & Laboratory Medicine, IU School of Medicine
Autophagy can be activated via MTORC1 down-regulation by amino acid deprivation and by certain chemicals such as rapamycin, torin, and niclosamide. Lysosome is the degrading machine for autophagy but has also been linked to MTORC1 activation through the Rag/RRAG GTPase pathway. This association raises the question of whether lysosome can be involved in the initiation of autophagy. Toward this end, we found that niclosamide, an MTORC1 inhibitor, was able to inhibit lysosome degradation and increase lysosomal permeability. Niclosamide was ineffective in inhibiting MTORC1 in cells expressing constitutively activated Rag proteins, suggesting that its inhibitory effects were targeted to the Rag-MTORC1 signaling system. This places niclosamide in the same category of bafilomycin A1 and concanamycin A, inhibitors of the vacuolar H(+)-ATPase, for its dependence on Rag GTPase in suppression of MTORC1. Surprisingly, classical lysosome inhibitors such as chloroquine, E64D, and pepstatin A were also able to inhibit MTORC1 in a Rag-dependent manner. These lysosome inhibitors were able to activate early autophagy events represented by ATG16L1 and ATG12 puncta formation. Our work established a link between the functional status of the lysosome in general to the Rag-MTORC1 signaling axis and autophagy activation. Thus, the lysosome is not only required for autophagic degradation but also affects autophagy activation. Lysosome inhibitors can have a dual effect in suppressing autophagy degradation and in initiating autophagy.

Browsing by Subject "Cell Biology"

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