Geetu Raheja
University of Illinois at Chicago
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Featured researches published by Geetu Raheja.
American Journal of Physiology-gastrointestinal and Liver Physiology | 2010
Geetu Raheja; Varsha Singh; Ke Ma; Redouane Boumendjel; Alip Borthakur; Ravinder K. Gill; Seema Saksena; Waddah A. Alrefai; Krishnamurthy Ramaswamy; Pradeep K. Dudeja
Clinical efficacy of probiotics in treating various forms of diarrhea has been clearly established. However, mechanisms underlying antidiarrheal effects of probiotics are not completely defined. Diarrhea is caused either by decreased absorption or increased secretion of electrolytes and solutes in the intestine. In this regard, the electroneutral absorption of two major electrolytes, Na(+) and Cl(-), occurs mainly through the coupled operation of Na(+)/H(+) exchangers and Cl(-)/OH(-) exchangers. Previous studies from our laboratory have shown that Lactobacillus acidophilus (LA) acutely stimulated Cl(-)/OH(-) exchange activity via an increase in the surface levels of the apical anion exchanger SLC26A3 (DRA). However, whether probiotics influence SLC26A3 expression and promoter activity has not been examined. The present studies were, therefore, undertaken to investigate the long-term effects of LA on SLC26A3 expression and promoter activity. Treatment of Caco-2 cells with LA for 6-24 h resulted in a significant increase in Cl(-)/OH(-) exchange activity. DRA mRNA levels were also significantly elevated in response to LA treatment starting as early as 8 h. Additionally, the promoter activity of DRA was increased by more than twofold following 8 h LA treatment of Caco-2 cells. Similar to the in vitro studies, in vivo studies using mice gavaged with LA also showed significantly increased DRA mRNA ( approximately 4-fold) and protein expression in the colonic regions as assessed by Western blot analysis and immunofluorescence. In conclusion, increase in DRA promoter activity and expression may contribute to the upregulation of intestinal electrolyte absorption and might underlie the potential antidiarrheal effects of LA.
American Journal of Physiology-gastrointestinal and Liver Physiology | 2010
Alip Borthakur; Arivarasu Natarajan Anbazhagan; Anoop Kumar; Geetu Raheja; Varsha Singh; Krishnamurthy Ramaswamy; Pradeep K. Dudeja
The major short-chain fatty acid (SCFA) butyrate is produced in the colonic lumen by bacterial fermentation of dietary fiber. Butyrate serves as primary fuel for the colonocytes and also ameliorates mucosal inflammation. Disturbed energy homeostasis seen in inflamed mucosa of inflammatory bowel disease patients has been attributed to impaired absorption of butyrate. Since sodium-coupled monocarboxylate transporter 1 (SMCT1, SLC5A8) has recently been shown to play a role in Na(+)-coupled transport of monocarboxylates, including SCFA, such as luminal butyrate, we examined the effects of proinflammatory TNF-α on SMCT1 expression and function and potential anti-inflammatory role of probiotic Lactobacillus species in counteracting the TNF-α effects. Rat intestinal epithelial cell (IEC)-6 or human intestinal Caco-2 cells were treated with TNF-α in the presence or absence of Lactobacilli culture supernatants (CS). TNF-α treatments for 24 h dose-dependently inhibited SMCT1-mediated, Na(+)-dependent butyrate uptake and SMCT1 mRNA expression in IEC-6 cells and SMCT1 promoter activity in Caco-2 cells. CS of L. plantarum (LP) stimulated Na(+)-dependent butyrate uptake (2.5-fold, P < 0.05), SMCT1 mRNA expression, and promoter activity. Furthermore, preincubating the cells with LP-CS followed by coincubation with TNF-α significantly attenuated the inhibitory effects of TNF-α on SMCT1 function, expression, and promoter activity. In vivo, oral administration of live LP enhanced SMCT1 mRNA expression in the colonic and ileal tissues of C57BL/6 mice after 24 h. Efficacy of LP or their secreted soluble factors to stimulate SMCT1 expression and function and to counteract the inhibitory effects of TNF-α on butyrate absorption could have potential therapeutic value.
American Journal of Physiology-gastrointestinal and Liver Physiology | 2012
Varsha Singh; Geetu Raheja; Alip Borthakur; Anoop Kumar; Ravinder K. Gill; Anas Alakkam; Jaleh Malakooti; Pradeep K. Dudeja
A major mechanism of electroneutral NaCl absorption in the human ileum and colon involves coupling of Na(+)/H(+) and Cl(-)/HCO(3)(-) exchangers. Disturbances in these mechanisms have been implicated in diarrheal conditions. Probiotics such as Lactobacillus have been indicated to be beneficial in the management of gastrointestinal disorders, including diarrhea. However, the molecular mechanisms underlying antidiarrheal effects of probiotics have not been fully understood. We have previously demonstrated Lactobacillus acidophilus (LA) to stimulate Cl(-)/HCO3- exchange activity via an increase in the surface levels and expression of the Cl(-)/HCO3- exchanger DRA in vitro and in vivo. However, the effects of LA on NHE3, the Na(+)/H(+) exchanger involved in the coupled electroneutral NaCl absorption, are not known. Current studies were, therefore, undertaken to investigate the effects of LA on the function and expression of NHE3 and to determine the mechanisms involved. Treatment of Caco2 cells with LA or its conditioned culture supernatant (CS) for 8-24 h resulted in a significant increase in Na(+)/H(+) exchange activity, mRNA, and protein levels of NHE3. LA-CS upregulation of NHE3 function and expression was also observed in SK-CO15 cells, a human colonic adenocarcinoma cell line. Additionally, LA treatment increased NHE3 promoter activity, suggesting involvement of transcriptional mechanisms. In vivo, mice gavaged with live LA showed significant increase in NHE3 mRNA and protein expression in the ileum and colonic regions. In conclusion, LA-induced increase in NHE3 expression may contribute to the upregulation of intestinal electrolyte absorption and might underlie the potential antidiarrheal effects of probiotics.
American Journal of Physiology-gastrointestinal and Liver Physiology | 2014
Varsha Singh; Anoop Kumar; Geetu Raheja; Arivarasu N. Anbazhagan; Shubha Priyamvada; Seema Saksena; Muhammad N. Jhandier; Ravinder K. Gill; Waddah A. Alrefai; Alip Borthakur; Pradeep K. Dudeja
Probiotics, including Lactobacilli, are commensal bacteria that have been used in clinical trials and experimental models for the prevention and treatment of diarrheal disorders. Our previous studies have shown that Lactobacillus acidophilus (LA) and its culture supernatant (CS) stimulated Cl(-)/HCO3 (-) exchange activity, acutely via an increase in the surface levels of downregulated in adenoma (DRA, SLC26A3) and in long-term treatments via increasing its expression involving transcriptional mechanisms. However, the role of LA in modulating DRA activity under inflammatory conditions is not known. Current in vitro studies using human intestinal epithelial Caco-2 cells examined the efficacy of LA or its CS in counteracting the inhibitory effects of interferon-γ (IFN-γ) on Cl(-)/HCO3 (-) exchange activity. Pretreatment of cells with LA or LA-CS for 1 h followed by coincubation with IFN-γ significantly alleviated the inhibitory effects of IFN-γ on Cl(-)/HCO3 (-) exchange activity. In the in vivo model of dextran sulfate sodium-induced experimental colitis (3% in drinking water for 7 days) in C57BL/6J mice, administration of live LA (3 × 10(9) colony-forming units) via oral gavage attenuated colonic inflammation. LA administration also counteracted the colitis-induced decrease in DRA mRNA and protein levels. Efficacy of LA or its secreted soluble factors in alleviating inflammation and inflammation-associated dysregulation of DRA activity could justify their therapeutic potential in inflammatory diarrheal diseases.
Gastroenterology | 2009
Ali Esmaili; Saad Nazir; Amika Singla; Amish K. Dudeja; Seema Saksena; Geetu Raheja; Waddah A. Alrefai; Ravinder K. Gill
Serotonin transporter (SERT) plays a critical role in regulating serotonin (5-HT) availability in the gut via reuptake of released serotonin. A decrease in SERT function and expression has been implicated in inflammatory bowel diseases and irritable colon. Hence, SERT is a potential pharmacological target in gastrointestinal disorders, however, very little is known regarding regulation of SERT in the human intestine. In this regard, EGF, a potent growth factor, is known to influence intestinal electrolyte and glucose transport processes and has protective effects on mucosa in models of colitis. Whether EGF regulates SERT function and expression in the human intestine is not known. The present studies were, therefore, designed to examine the regulation of SERT by EGF utilizing Caco2 cells grown on Transwell inserts as an In Vitro model. SERT activity was measured as Na+ and Cldependent 3[H] 5-HT uptake in fully differentiated cell monolayers. SERT mRNA abundance was determined by real time QRT-PCR. SERT promoter activity was assessed by luciferase assay in cells transiently transfected with promoter constructs. Treatment of Caco-2 cells with EGF from basolateral side (5-10ng/ml) for 24h significantly stimulated SERT activity (~50%, P<0.005). However, acute treatment with EGF (1-2 h) did not affect SERT function in Caco-2 cells. Corresponding with increased function at 24h, EGF treatment resulted in up-regulation of SERT mRNA levels (~1.8 fold) compared to control. For studying the regulation of SERT gene by EGF, a 873 bp (-871/+2) SERT promoter fragment was cloned upstream to the luciferase reporter gene and was found to be highly active when transfected in Caco2 cells. EGF treatment (10 ng/ml) for 8-24h resulted in significant stimulation in SERT promoter activity (~50-60%; P<0.05). Inhibition of EGF receptor (EGFR) tyrosine kinase activity by PD168393 (1nM) blocked the stimulatory effects of EGF on SERT promoter. Studies utilizing progressive deletion constructs of the SERT promoter indicated that the putative EGF responsive elements are in the -672/+472 region of the promoter. Conclusion: Our findings demonstrate transcriptional regulation of SERT by EGF via EGFR. These data define novel mechanisms of modulation of SERT function and expression in intestinal epithelium that may be relevant to therapeutic benefits of EGF in diarrheal diseases associated with altered 5-HT availability. [Supported by NIDDK/Dept of Veteran Affairs].
Gastroenterology | 2011
Varsha Singh; Geetu Raheja; Seema Saksena; Ravinder K. Gill; Anas Alakkam; Alip Borthakur; Gail Hecht; Waddah A. Alrefai; Pradeep K. Dudeja
Varsha Singh,* Anoop Kumar,* Geetu Raheja, Arivarasu N. Anbazhagan, Shubha Priyamvada, Seema Saksena, Muhammad Nauman Jhandier, Ravinder K. Gill, Waddah A. Alrefai, Alip Borthakur, and Pradeep K. Dudeja Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago and Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; and Singhania University, Pacheri Bari, Rajasthan, India
Gastroenterology | 2010
Alip Borthakur; Arivarasu Natarajan Anbazhagan; Anoop Kumar; Geetu Raheja; Varsha Singh; Krishnamurthy Ramaswamy; Pradeep K. Dudeja
Background and Aim: Dysregulated epithelial secretory function can lead to the clinical manifestation of diarrhea. Intestinal fluid secretion is driven by active Clion secretion and is dependent on the availability of O2 for generation of cellular energy. Hydroxylases are the primary intracellular sensors of O2 availability, and we have previously shown that hydroxylase inhibition attenuates colonic epithelial secretory capacity. Here, we sought to investigate the molecular mechanisms involved and to test the efficacy of hydroxylase inhibitors in preventing diarrhea In Vivo.Methods: The pan-hydroxylase inhibitor dimethyloxallyl glycine (DMOG) was used to inhibit hydroxylase activity. Clsecretion was measured as changes in short circuit current across monolayers of T84 cells or muscle-stripped segments of mouse colon. Western blotting and biotinylation techniques were used to assess protein expression. DMOG effects were also tested In Vivo in a mouse allergic (ovalbumin) model of diarrhea. Results: As previously reported treatment of T84 cells with DMOG (1 mM) reduced Clsecretory responses to the Ca2+ and cAMP-dependent agonists, carbachol (CCh) and forskolin (FSK), to 20.2 ± 2.6% and 38.8 ± 4.8% of controls, respectively (n=16; p<0.001). To determine molecular mechanisms involved we analysed the activity of transport proteins comprising the Clsecretory pathway. Hydroxylase inhibition did not alter apical Clor basolateral K+ conductances but significantly reduced the activity of the Na+/K+ATPase, the energy-dependent step of Clsecretion, to 42.7% ± 5.5% of controls (n=5; p≤0.01). However, DMOG did not alter total cellular or surface expression of the ATPase. Cellular ATP, required to drive pump activity, was reduced to 67% ± 8.5% of controls (n=6; p≤0.05) by DMOG. Intraperitoneal injection of mice with DMOG (320 mg/kg; 24 hrs) attenuated colonic secretory responses to CCh and FSK to 54.8 ± 6.1% (n=11; p≤0.001) and 72.4 ± 11.5% (n=11; p≤0.05) of those of controls, respectively. Furthermore, in an In Vivo mouse model of allergic diarrhea, DMOG pretreatment reduced the occurrence of diarrhea by 80% compared to controls (n=10). Conclusion: Our studies show that hydroxylase inhibition in colonic epithelial cells inhibits secretory function. This antisecretory effect is mediated by attenuation of Na+/K+-ATPase pump activity, either directly, or secondary to the depletion of cellular ATP. Our data suggest that by virtue of their ability to regulate epithelial transport In Vitro and In Vivo, hydroxylases present a promising target for the development of novel anti-diarrheal agents that act by directly modulating transport protein function.
Indian Journal of Experimental Biology | 1998
Geetu Raheja; Ravinder Kaur Gill; S. Kumar; Safrun Mahmood; Akhtar Mahmood
Gastroenterology | 2010
Geetu Raheja; Varsha Singh; Muhammad N. Jhandier; Jaleh Malakooti; Redouane Boumendjel; Alip Borthakur; Ravinder K. Gill; Waddah A. Alrefai; Krishnamurthy Ramaswamy; Pradeep K. Dudeja
Gastroenterology | 2012
Muhammad N. Jhandier; Varsha Singh; Geetu Raheja; Arivarasu Natarajan Anbazhagan; Jaleh Malakooti; Waddah A. Alrefai; Ravinder K. Gill; Pradeep K. Dudeja