[Show abstract][Hide abstract] ABSTRACT: Alterations in epithelial cell polarity and in the subcellular distributions of epithelial ion transport proteins are key molecular consequences of acute kidney injury and intracellular energy depletion. AMP-activated protein kinase (AMPK), a cellular energy sensor, is rapidly activated in response to renal ischemia, and we demonstrate that its activity is upregulated by energy depletion in Madin-Darby canine kidney (MDCK) cells. We hypothesized that AMPK activity may influence the maintenance or recovery of epithelial cell organization in mammalian renal epithelial cells subjected to energy depletion. MDCK cells were ATP depleted through a 1-h incubation with antimycin A and 2-deoxyglucose. Immunofluoresence localization demonstrated that this regimen induces mislocalization of the Na-K-ATPase from its normal residence at the basolateral plasma membrane to intracellular vesicular compartments. When cells were pretreated with the AMPK activator metformin before energy depletion, basolateral localization of Na-K-ATPase was preserved. In MDCK cells in which AMPK expression was stably knocked down with short hairpin RNA, preactivation of AMPK with metformin did not prevent Na-K-ATPase redistribution in response to energy depletion. In vivo studies demonstrate that metformin activated renal AMPK and that treatment with metformin before renal ischemia preserved cellular integrity, preserved Na-K-ATPase localization, and led to reduced levels of neutrophil gelatinase-associated lipocalin, a biomarker of tubular injury. Thus AMPK may play a role in preserving the functional integrity of epithelial plasma membrane domains in the face of energy depletion. Furthermore, pretreatment with an AMPK activator before ischemia may attenuate the severity of renal tubular injury in the context of acute kidney injury.
Full-text · Article · Aug 2011 · AJP Renal Physiology
[Show abstract][Hide abstract] ABSTRACT: Renal cyst development and expansion in autosomal dominant polycystic kidney disease (ADPKD) involves both fluid secretion and abnormal proliferation of cyst-lining epithelial cells. The chloride channel of the cystic fibrosis transmembrane conductance regulator (CFTR) participates in secretion of cyst fluid, and the mammalian target of rapamycin (mTOR) pathway may drive proliferation of cyst epithelial cells. CFTR and mTOR are both negatively regulated by AMP-activated protein kinase (AMPK). Metformin, a drug in wide clinical use, is a pharmacological activator of AMPK. We find that metformin stimulates AMPK, resulting in inhibition of both CFTR and the mTOR pathways. Metformin induces significant arrest of cystic growth in both in vitro and ex vivo models of renal cystogenesis. In addition, metformin administration produces a significant decrease in the cystic index in two mouse models of ADPKD. Our results suggest a possible role for AMPK activation in slowing renal cystogenesis as well as the potential for therapeutic application of metformin in the context of ADPKD.
Full-text · Article · Feb 2011 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: We report the case of a 14-year-old boy who presented with hematuria and decreased kidney function as initial manifestations of acute lymphoblastic leukemia (ALL). Computed tomography of the abdomen showed extensive retroperitoneal lymphadenopathy and bilateral nephromegaly. The patient's kidney biopsy specimen showed a dense monomorphous interstitial infiltrate of small round blue cells with significant nuclear atypia. Immunohistochemical workup showed positive staining for CD20, CD10, and terminal deoxynucleotidyl transferase (TdT), consistent with ALL. The patient underwent induction chemotherapy, attained remission 4 weeks after induction, and presently is stable in the consolidation phase of chemotherapy. This is an unusual case of ALL involving both kidneys with initial presenting signs of hematuria and decreased kidney function.
No preview · Article · Nov 2010 · American Journal of Kidney Diseases
[Show abstract][Hide abstract] ABSTRACT: The Na(+),K(+)-ATPase is the major active transport protein found in the plasma membranes of most epithelial cell types. The regulation of Na(+),K(+)-ATPase activity involves a variety of mechanisms, including regulated endocytosis and recycling. Our efforts to identify novel Na(+),K(+)-ATPase binding partners revealed a direct association between the Na(+),K(+)-ATPase and AS160, a Rab-GTPase-activating protein. In COS cells, coexpression of AS160 and Na(+),K(+)-ATPase led to the intracellular retention of the sodium pump. We find that AS160 interacts with the large cytoplasmic NP domain of the α-subunit of the Na(+),K(+)-ATPase. Inhibition of the activity of the adenosine monophosphate-stimulated protein kinase (AMPK) in Madin-Darby canine kidney cells through treatment with Compound C induces Na(+),K(+)-ATPase endocytosis. This effect of Compound C is prevented through the short hairpin RNA-mediated knockdown of AS160, demonstrating that AMPK and AS160 participate in a common pathway to modulate the cell surface expression of the Na(+),K(+)-ATPase.
Full-text · Article · Oct 2010 · Molecular biology of the cell
[Show abstract][Hide abstract] ABSTRACT: Mycophenolate Mofetil (MMF) is a frequently used medication for the maintenance of immunosuppression in pediatric renal transplant patients. It is known to cause mild gastrointestinal side effects. Severe colitis due to MMF is rare and is only described in adults. We report 2 children who presented with severe colitis due to MMF. Infectious and other causes of diarrhea were ruled out. Our patients had diverse histologic findings on colonic biopsies. Patient 1 had histologic features similar to inflammatory bowel disease and patient 2 to graft versus host disease. Withdrawal of MMF resulted in the complete resolution of symptoms in both patients suggesting a causal association. These cases underscore the importance of considering MMF-induced colitis in any patient who presents with diarrhea while on MMF therapy.
No preview · Article · Aug 2009 · Journal of clinical gastroenterology
[Show abstract][Hide abstract] ABSTRACT: The tasks of defining, maintaining and defending the composition of the body's inventory of internal compartments all fall to its contingent of polarized epithelial cells (Muth and Caplan, 2003). The cells' ability to become and stay polarized suggests that they detect physical cues from their environments and respond to these cues by creating the structural and functional asymmetries that characterize the polarized state. These cues derive primarily from contacts that each cell makes with its neighboring cells and with the extracellular matrix. The establishment of these contacts initiates a cascade of events involving activation of protein kinases and the assembly of protein complexes, which together ultimately lead to the demarcation and construction of the apical and basolateral domains of the plasma membrane.
Full-text · Article · Feb 2009 · Developmental Cell
[Show abstract][Hide abstract] ABSTRACT: An enormous body of research has been focused on exploring the mechanisms through which epithelial cells establish their characteristic polarity. It is clear that under normal circumstances cell-cell contacts mediated by the calcium-dependent adhesion proteins of the intercellular adhesion junctions are required to initiate complete polarization. Furthermore, formation of the tight, or occluding, junctions that limit paracellular permeability has long been thought to help to establish polarity by preventing the diffusion of membrane proteins between the two plasmalemmal domains. This review will discuss several selected kinases and protein complexes and highlight their relevance to transporting epithelial cell polarization.
Recent work has shed new light on the roles of junctional complexes in establishing and maintaining epithelial cell polarity. In addition, work from several laboratories suggests that the formation of these junctions is tied to processes that regulate cellular energy metabolism.
Junctional complexes and energy sensing kinases constitute a novel class of machinery whose capacity to generate and modulate epithelial cell polarity is likely to have wide ranging and important physiological ramifications.
Full-text · Article · Oct 2008 · Current Opinion in Nephrology and Hypertension
[Show abstract][Hide abstract] ABSTRACT: Dinitrophenol, a chemical currently used as an insecticide, is known to uncouple mitochondrial oxidative phosphorylation. A component of explosives, it has also been used in the past as a food coloring and clothing dye. In the 1930s, physicians prescribed it for weight loss, but this practice was discontinued when reports of cataracts, deaths, and other adverse outcomes came to light. We describe in our report the overdose and fatality of a teenager who purchased the product as a weight loss dietary supplement by mail order. We also describe a laboratory method that allowed postmortem determination of the dinitrophenol concentration in the victim's serum. Her death, despite prompt medical treatment, underscores the danger of dinitrophenol. The easy accessibility and apparent resurgent interest in dinitrophenol as a weight loss agent is extremely timely and troubling.
No preview · Article · Feb 2005 · Clinical Toxicology
[Show abstract][Hide abstract] ABSTRACT: Abbreviations used in this paper: sodium pump, Na + , K + -ATPase; adenosine monophosphate-stimulated protein kinase (AMPK); Acetyl CoA carboxylase (ACC). ABSTRACT The Na + , K + -ATPase is the major active transport protein found in the plasma membranes of most epithelial cell types. The regulation of Na + , K + -ATPase activity involves a variety of mechanisms, including regulated endocytosis and recycling. Our efforts to identify novel Na + , K + -ATPase binding partners revealed a direct association between the Na + , K + -ATPase and AS160, a Rab-GTPase-activating protein. In COS cells, coexpression of AS160 and Na + , K + -ATPase led to the intracellular retention of the sodium pump. We find that AS160 interacts with the large cytoplasmic NP domain of the α-subunit of the Na + , K + -ATPase. Inhibition of the activity of the adenosine monophosphate-stimulated protein kinase (AMPK) in MDCK cells through treatment with Compound C induces Na + , K + -ATPase endocytosis. This effect of Compound C is prevented through the shRNA-mediated knockdown of AS160, demonstrating that AMPK and AS160 participate in a common pathway to modulate the cell surface expression of the Na + , K + -ATPase.