Joseph Alroy

Fission and selective fusion govern mitochondrial segregation and elimination by autophagy

Accumulation of depolarized mitochondria within β‐cells has been associated with oxidative damage and development of diabetes. To determine the source and fate of depolarized mitochondria, individual mitochondria were photolabeled and tracked through fusion and fission. Mitochondria were found to go through frequent cycles of fusion and fission in a ‘kiss and run’ pattern. Fission events often generated uneven daughter units: one daughter exhibited increased membrane potential (Δψm) and a high probability of subsequent fusion, while the other had decreased membrane potential and a reduced probability for a fusion event. Together, this pattern generated a subpopulation of non‐fusing mitochondria that were found to have reduced Δψm and decreased levels of the fusion protein OPA1. Inhibition of the fission machinery through DRP1K38A or FIS1 RNAi decreased mitochondrial autophagy and resulted in the accumulation of oxidized mitochondrial proteins, reduced respiration and impaired insulin secretion. Pulse chase and arrest of autophagy at the pre‐proteolysis stage reveal that before autophagy mitochondria lose Δψm and OPA1, and that overexpression of OPA1 decreases mitochondrial autophagy. Together, these findings suggest that fission followed by selective fusion segregates dysfunctional mitochondria and permits their removal by autophagy.

Cardiotoxicity of the cancer therapeutic agent imatinib mesylate

Imatinib mesylate (Gleevec) is a small-molecule inhibitor of the fusion protein Bcr-Abl, the causal agent in chronic myelogenous leukemia. Here we report ten individuals who developed severe congestive heart failure while on imatinib and we show that imatinib-treated mice develop left ventricular contractile dysfunction. Transmission electron micrographs from humans and mice treated with imatinib show mitochondrial abnormalities and accumulation of membrane whorls in both vacuoles and the sarco- (endo-) plasmic reticulum, findings suggestive of a toxic myopathy. With imatinib treatment, cardiomyocytes in culture show activation of the endoplasmic reticulum (ER) stress response, collapse of the mitochondrial membrane potential, release of cytochrome c into the cytosol, reduction in cellular ATP content and cell death. Retroviral gene transfer of an imatinib-resistant mutant of c-Abl, alleviation of ER stress or inhibition of Jun amino-terminal kinases, which are activated as a consequence of ER stress, largely rescues cardiomyocytes from imatinib-induced death. Thus, cardiotoxicity is an unanticipated side effect of inhibition of c-Abl by imatinib.

Imagable 4T1 model for the study of late stage breast cancer

BackgroundThe 4T1 mouse mammary tumor cell line is one of only a few breast cancer models with the capacity to metastasize efficiently to sites affected in human breast cancer. Here we describe two 4T1 cell lines modified to facilitate analysis of tumor growth and metastasis and evaluation of gene function in vivo. New information regarding the involvement of innate and acquired immunity in metastasis and other characteristics of the model relevant to its use in the study of late stage breast cancer are reported.MethodsThe lines were engineered for stable expression of firefly luciferase to allow tracking and quantitation of the cells in vivo. Biophotonic imaging was used to characterize growth and metastasis of the lines in vivo and an improved gene expression approach was used to characterize the basis for the metastatic phenotype that was observed.ResultsGrowth of cells at the primary site was biphasic with metastasis detected during the second growth phase 5–6 weeks after introduction of the cells. Regression of growth, which occurred in weeks 3–4, was associated with extensive necrosis and infiltration of leukocytes. Biphasic tumor growth did not occur in BALB/c SCID mice indicating involvement of an acquired immune response in the effect. Hematopoiesis in spleen and liver and elevated levels of circulating leukocytes were observed at week 2 and increased progressively until death at week 6–8. Gene expression analysis revealed an association of several secreted factors including colony stimulatory factors, cytokines and chemokines, acute phase proteins, angiogenesis factors and ECM modifying proteins with the 4T1 metastatic phenotype. Signaling pathways likely to be responsible for production of these factors were also identified.ConclusionThe production of factors that stimulate angiogenesis and ECM modification and induce hematopoiesis, recruitment and activation of leukocytes suggest that 4T1 tumor cells play a more direct role than previously appreciated in orchestrating changes in the tumor environment conducive to tumor cell dissemination and metastasis. The new cell lines will greatly facilitate the study of late stage breast and preclinical assessment of cancer drugs and other therapeutics particularly those targeting immune system effects on tumor metastasis.

Favorable effect of VEGF gene transfer on ischemic peripheral neuropathy

Ischemic peripheral neuropathy is a frequent, irreversible complication of lower extremity vascular insufficiency. We investigated whether ischemic peripheral neuropathy could be prevented and/or reversed by gene transfer of an endothelial cell mitogen designed to promote therapeutic angiogenesis. Intramuscular gene transfer of naked DNA encoding vascular endothelial growth factor (VEGF) simultaneously with induction of hindlimb ischemia in rabbits abrogated the substantial decrease in motor and sensory nerve parameters, and nerve function recovered promptly. When gene transfer was administered 10 days after induction of ischemia, nerve function was restored earlier and/or recovered faster than in untreated rabbits. These findings are due in part to enhanced hindlimb perfusion. In addition, however, the demonstration of functional VEGF receptor expression by Schwann cells indicates a direct effect of VEGF on neural integrity as well. These findings thus constitute a new paradigm for the treatment of ischemic peripheral neuropathy.

The Structure and Function of Intercellular Junctions in Cancer

Publisher Summary Intercellular junctions are a set of structurally complex membrane components that are incorporated into the general plasma membrane at the sites of close cell-to-cell apposition. The primary function of some types of junctions, such as gap junctions, remains obscure; this is unfortunate because a considerable body of information on the occurrence, biochemical ultrastructure, and physical properties of junctions suggests that they probably do play a central role in important biological phenomena. The quantitative evaluations of the occurrence of junctions are subjective in most of the reports, although there are a few reports in which the data were obtained by quantitative electron microscopy techniques. There are a number of ways in which genes of neoplastic transformation may influence intercellular junction structure and function. Additional research is required to define the contribution of tumor gene products to the pathogenesis of junctional abnormalities in tumors and to elucidate the roles, if any, of these cell membrane defects in malignant growth.

Lectin histochemistry of mammalian endothelium

SummaryLectin-histochemical studies were performed on formalin-fixed, paraffin-embedded tissues from ten mammalian species to demonstrate the pattern of carbohydrate residues in vascular endothelium. Ten different biotinylated lectins were used as probes and avidin-biotin-peroxidase complex (ABC) was used as visualant. Ricinus communis agglutinin-I (RCA-I) and wheat germ agglutinin (WGA) stained vascular endothelium in all species. Peanut agglutinin (PNA) stained vascular endothelium in all species only after preincubation with neuraminidase. Bandeirea simplicifolia agglutinin-I (BS-I) stained vascular endothelium in all species but human, while, Ulex europeus agglutinin-I (UEA-I) stained only human endothelium. Individual differences in staining of human vascular endothelium were noted with BS-I and succinylated-WGA (SWGA). Similarly, individual differences in staining of animal vascular endothelium were noted with soybean agglutinin (SBA) after preincubation with neuraminidase. Finally, Concanavalia ensiformis agglutinin (Con A), Dolichos biflorus agglutinin (DBA) and Lens culinaris agglutinin (LCA) did not stain vascular endothehuman in any of the species studied.

Apoptosis as the Mechanism of Neurodegeneration in Batten's Disease

Abstract: Battens disease is a genetic neurodegenerative disease of childhood. Its hallmarks are retinitis pigmentosa and neuronal degeneration. As some types of photoreceptor death in mice are mediated by apoptosis, we investigated whether apoptosis is responsible for retinal and neuronal degeneration in the late infantile and juvenile forms of Battens disease. Using the terminal dUDP nick end‐labeling (TUNEL) staining method, we detected apoptotic neuronal cells in brain from patients and a canine model and in brain and retina from an ovine model for Battens disease. We confirmed apoptosis by flow cytometry, electron microscopy, and DNA laddering. This is the first inherited neurodegenerative disease involving brain and retina in which apoptosis has been established as the mechanism of neuronal and photoreceptor cell death in both humans and animal models.

Pheochromocytoma cell lines from heterozygous neurofibromatosis knockout mice

Abstract. Transplantable tumors and cell lines have been developed from pheochromocytomas arising in mice with a heterozygous knockout mutation of the neurofibromatosis gene, Nf1. Nf1 encodes a ras-GTPase-activating protein, neurofibromin, and mouse pheochromocytoma (MPC) cells in primary cultures typically show extensive spontaneous neuronal differentiation that may result from the loss of the remaining wild-type allele and defective regulation of ras signaling. However, all MPC cell lines express neurofibromin, suggesting that preservation of the wild-type allele may be required to permit the propagation of MPC cells in vitro. MPC lines differ from PC12 cells in that they express both endogenous phenylethanolamine N-methyltransferase (PNMT) and full-length PNMT reporter constructs. PNMT expression is increased by dexamethasone and by cell-cell contact in suspension cultures. Mouse pheochromocytomas are a new tool for studying genes and signaling pathways that regulate cell growth and differentiation in adrenal medullary neoplasms and are a unique model for studying the regulation of PNMT expression.

Correlation between numbers of desmosomes and the aggressiveness of transitional cell carcinoma in human urinary bladder.

Quantitative electron microscopy has been used to examine the correlation between numbers of desmosomes and the histopathological grade and stage of papillary transitional cell carcinomas in human urinary bladder. Numbers of desmosomes (desmosomal density) per 100 μm of cell perimeter were quantitated in 6 examples of normal epithelium, 11 noninvasive papillary transitional cell carcinomas, 8 invasive transitional cell carcinomas arising from papillary lesions, 3 invasive transitional cell carcinomas which had prominent foci of glandular and squamous differentiation, and 1 squamous cell carcinoma. Desmosomal densities were increased in noninvasive transitional cell carcinomas, as compared with normal epithelium, but decreased in invasive transitional cell carcinomas. However, in areas of glandular or squamous differentiation in invasive tumors, desmosomal densities were increased, possibly reflecting the changes in cell phenotype. The decrease in numbers of desmosomes in invasive transitional cell carcinomas may contribute to reductions in cell adhesiveness.

Anti-inflammatory effect of topical nanocrystalline silver cream on allergic contact dermatitis in a guinea pig model.

The anti‐inflammatory activity of topical nanocrystalline silver cream was assessed and compared with the effects of topical steroids and currently available immunosuppressants using a guinea pig model of allergic contact dermatitis. Dermatitis was induced with dinitrochlorobenzene and treated with different concentrations of nanocrystalline silver, medium and high potency steroids, tacrolimus and pimecrolimus, or appropriate vehicles once daily for 5 days. Erythema was evaluated daily (on a score of 0 to 4, from absent to very severe) and histopathology of the skin biopsies was evaluated after 5 days of treatment. Prior to treatment, the average scores of erythema in all the groups were in the range of 3+ to 4+. In the no treatment and vehicles groups these scores remained at about this level for the subsequent 5 days of the study. Nanocrystalline silver reduced erythema within 1 day of treatment in a concentration‐dependent manner with significant reduction at silver concentrations of 0.5% and 1% (P < 0.05) and this reduction progressed throughout the study period. Steroids and immunosuppressants produced similar decreases in erythema, with no significant differences compared to 0.5% and 1% nanocrystalline silver. In skin biopsies scored for degree of inflammatory response, effects of treatments mirrored erythema results. This study suggests that nanocrystalline silver cream may have therapeutic potential for topical treatment of inflammatory skin diseases.