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1.  Downregulation of plasma insulin levels and hepatic PPAR expression during the first week of caloric restriction in mice 
Experimental gerontology  2007;43(3):146-153.
Calorie restriction extends lifespan by decreasing the rate of tumor formation, an effect occurring within 8 weeks of initiating a restricted diet. Our goal was to define how the first weeks of a calorie restricted diet (60% of ad libitum calories) affects putative mediators of the calorie restriction phenotype, focusing on regulators of fatty acid biosynthesis. In C57Bl/6 mice, insulin decreased over 50% (p<0.05) during the first week of calorie restriction whereas IGF-1 was unaffected. In the liver, PPAR mRNA fell to 13% of baseline after one week of calorie restriction (p<0.05), whereas hepatic SREBP-1c and SIRT1 mRNA levels were unaffected. No changes in abdominal or subcutaneous adipose tissue were observed until after 8 weeks of caloric restriction. We conclude that calorie restriction-induced decreases in insulin and hepatic PPAR are rapid enough to support a role for these molecules in triggering the initial phase of the calorie restriction phenotype.
PMCID: PMC2350197  PMID: 18053669
Aging; Caloric Restriction
2.  A high-fat diet decreases AMPK activity in multiple tissues in the absence of hyperglycemia or systemic inflammation in rats 
Consumption of a high-fat diet (HFD) in experimental animal models initiates a series of molecular events and outcomes, including insulin resistance and obesity, that mimic the metabolic syndrome in humans. The relationship among, and order of, the molecular events linking a diet high in fat to pathologies is often unclear. In the present study, we provide several novel insights into the relationship between a HFD and AMP-activated protein kinase (AMPK), a key regulator of cellular metabolism and whole-body energy balance. HFD substantially decreased the activities of both iso-forms of AMPK in white adipose tissue, heart, and liver. These decreases in AMPK activity occurred in the absence of decreased AMPK transcription, systemic inflammation, hyperglycemia, or elevated levels of free fatty acids. The HFD-induced decrease in AMPK activity was associated with systemic insulin resistance and hyperleptinemia. In blood, >98 % of AMPK activity was localized in agranulocytes as the α1 isoform. In contrast to the solid tissues studied, AMPK activities were not altered by HFD in granulocytes or agranulocytes. We conclude that HFD-induced obesity causes a broad, non-tissue, or isoform-specific lowering of AMPK activity. Given the central position AMPK plays in whole-body energy balance, this decreased AMPK activity may play a previously unrecognized role in obesity and its associated pathologies.
PMCID: PMC3644018  PMID: 22941749
Obesity; Diabetes; Adipose; Blood
3.  High-content adhesion assay to address limited cell samples† 
Cell adhesion is a broad topic in cell biology that involves physical interactions between cells and other cells or the surrounding extracellular matrix, and is implicated in major research areas including cancer, development, tissue engineering, and regenerative medicine. While current methods have contributed significantly to our understanding of cell adhesion, these methods are unsuitable for tackling many biological questions requiring intermediate numbers of cells (102–105), including small animal biopsies, clinical samples, and rare cell isolates. To overcome this fundamental limitation, we developed a new assay to quantify the adhesion of ~102–103 cells at a time on engineered substrates, and examined the adhesion strength and population heterogeneity via distribution-based modeling. We validated the platform by testing adhesion strength of cancer cells from three different cancer types (breast, prostate, and multiple myeloma) on both IL-1β activated and non-activated endothelial monolayers, and observed significantly increased adhesion for each cancer cell type upon endothelial activation, while identifying and quantifying distinct subpopulations of cell-substrate interactions. We then applied the assay to characterize adhesion of primary bone marrow stromal cells to different cardiac fibroblast-derived matrix substrates to demonstrate the ability to study limited cell populations in the context of cardiac cell-based therapies. Overall, these results demonstrate the sensitivity and robustness of the assay as well as its ability to enable extraction of high content, functional data from limited and potentially rare primary samples. We anticipate this method will enable a new class of biological studies with potential impact in basic and translational research.
PMCID: PMC3832292  PMID: 23426645
4.  Pathophysiological Defects and Transcriptional Profiling in the RBM20-/- Rat Model 
PLoS ONE  2013;8(12):e84281.
Our recent study indicated that RNA binding motif 20 (Rbm20) alters splicing of titin and other genes. The current goals were to understand how the Rbm20-/- rat is related to physiological, structural, and molecular changes leading to heart failure. We quantitatively and qualitatively compared the expression of titin isoforms between Rbm20-/- and wild type rats by real time RT-PCR and SDS agarose electrophoresis. Isoform changes were linked to alterations in transcription as opposed to translation of titin messages. Reduced time to exhaustion with running in knockout rats also suggested a lower maximal cardiac output or decreased skeletal muscle performance. Electron microscopic observations of the left ventricle from knockout animals showed abnormal myofibril arrangement, Z line streaming, and lipofuscin deposits. Mutant skeletal muscle ultrastructure appeared normal. The results suggest that splicing alterations in Rbm20-/- rats resulted in pathogenic changes in physiology and cardiac ultrastructure. Secondary changes were observed in message levels for many genes whose splicing was not directly affected. Gene and protein expression data indicated the activation of pathophysiological and muscle stress-activated pathways. These data provide new insights on Rbm20 function and how its malfunction leads to cardiomyopathy.
PMCID: PMC3868568  PMID: 24367651
5.  RBM20, a gene for hereditary cardiomyopathy, regulates titin splicing 
Nature medicine  2012;18(5):766-773.
Alternative splicing plays a major role in the adaptation of cardiac function exemplified by the isoform switch of titin, which adjusts ventricular filling. We previously identified a rat strain deficient in titin splicing. Using genetic mapping, we found a loss-of-function mutation in RBM20 as the underlying cause for the pathological titin isoform expression. Mutations in human RBM20 have previously been shown to cause dilated cardiomyopathy. We showed that the phenotype of Rbm20 deficient rats resembles the human pathology. Deep sequencing of the human and rat cardiac transcriptome revealed an RBM20 dependent regulation of alternative splicing. Additionally to titin we identified a set of 30 genes with conserved regulation between human and rat. This network is enriched for genes previously linked to cardiomyopathy, ion-homeostasis, and sarcomere biology. Our studies emphasize the importance of posttranscriptional regulation in cardiac function and provide mechanistic insights into the pathogenesis of human heart failure.
PMCID: PMC3569865  PMID: 22466703
6.  Caloric restriction does not alter effects of aging in cardiac side population cells 
Age  2010;33(3):351-361.
The aged heart displays a loss of cardiomyocyte number and function, possibly due to the senescence and decreased regenerative potential that has been observed in some cardiac progenitor cells. An important cardiac progenitor that has not been studied in the context of aging is the cardiac side population (CSP) cell. To address this, flow cytometry-assisted cell sorting was used to isolate CSP cells from adult (6–10 months old) and aged (24–32 months old) C57Bl/6 mice that were fed either a control diet or an anti-aging diet (caloric restriction, CR). Aging caused a 2.3-fold increase in the total number of CSP cells and a 3.2-fold increase in the cardiomyogenic sca1+/CD31− subpopulation. Aging did not affect markers of proliferation or senescence, including telomerase activity and expression of cell cycle genes, in sca1+/CD31− CSP cells. In contrast, the aged cells had reduced expression of genes associated with differentiation, including smooth muscle actin and cardiac muscle actin (5.1- and 3.2-fold, respectively). None of these age effects were altered by CR diet. Therefore, it appears that the manner in which CSP cells age is distinct from the aging of post-mitotic tissue (and perhaps other progenitor cells) that can often be attenuated by CR.
PMCID: PMC3168602  PMID: 20922487
Adult stem cell; Cardiac regeneration; CR; CSP; Sca1; CD31
7.  Caloric restriction attenuates the age-associated increase of adipose-derived stem cells but further reduces their proliferative capacity 
Age  2010;33(2):107-118.
White adipose tissue is a promising source of mesenchymal stem cells. Currently, little is known about the effect of age and caloric restriction (CR) on adipose-derived stem cells (ASC). This is important for three reasons: firstly, age and CR cause extensive remodeling of WAT; it is currently unknown how this remodeling affects the resident stem cell population. Secondly, stem cell senescence has been theorized as one of the causes of aging and could reduce the utility of a stem cell as a reagent. Thirdly, the mechanism by which CR extends lifespan is currently not known, one theory postulates that CR maintains the resident stem cell population in youthful “fit” state. For the purpose of this study, we define ASC as lineage negative (lin−)/CD34+(low)/CD31−. We show that aging increases the abundance of ASC and the expression of Cdkn2a 9.8-fold and Isl1 60.6-fold. This would suggest that aging causes an accumulation of non-replicative ASC. CR reduced the percentage of ASC in the lin− SVF while also reducing colony forming ability. Therefore, CR appears to have anti-proliferative effects on ASC that may be advantageous from the perspective of cancer, but our data raises the possibility that it may be disadvantageous for regenerative medicine applications.
PMCID: PMC3127466  PMID: 20628827
Stem cells; Aging; Caloric restriction; Adipose tissue; Regeneration; Cancer
11.  A Low Dose of Dietary Resveratrol Partially Mimics Caloric Restriction and Retards Aging Parameters in Mice 
PLoS ONE  2008;3(6):e2264.
Resveratrol in high doses has been shown to extend lifespan in some studies in invertebrates and to prevent early mortality in mice fed a high-fat diet. We fed mice from middle age (14-months) to old age (30-months) either a control diet, a low dose of resveratrol (4.9 mg kg−1 day−1), or a calorie restricted (CR) diet and examined genome-wide transcriptional profiles. We report a striking transcriptional overlap of CR and resveratrol in heart, skeletal muscle and brain. Both dietary interventions inhibit gene expression profiles associated with cardiac and skeletal muscle aging, and prevent age-related cardiac dysfunction. Dietary resveratrol also mimics the effects of CR in insulin mediated glucose uptake in muscle. Gene expression profiling suggests that both CR and resveratrol may retard some aspects of aging through alterations in chromatin structure and transcription. Resveratrol, at doses that can be readily achieved in humans, fulfills the definition of a dietary compound that mimics some aspects of CR.
PMCID: PMC2386967  PMID: 18523577

Results 1-11 (11)