Cardiovascular Aging in the Female F344xBN Rat Model

Despite continued advances in medical care, cardiovascular disease (CVD) remains the leading cause of death for American women [1]. Although humans and non-human primates are the only mammals to experience menses, rodent models are commonly used to study age-associated cardiovascular alterations due to similar ovarian aging, low expense, and short lifetime to investigate cardiovascular aging. Previous studies have found that aging in the female rodent is characterized by increased ventricular apoptosis, elevations in oxidative-nitrosative stress, ventricular remodeling, increased collagen content, mild systolic and diastolic dysfunction, and reduced occurrence of arrhythmias compared to males [2-7]. Similarly, age-associated alterations in the female rodent aorta have been shown to include increased proliferation/migration of vascular smooth muscle cells (VSMC) and endothelial dysfunction [8, 9]. However, no study has investigated the age-associated alterations in the female heart and aorta of the National Institute of Aging (NIA) approved Fischer 344/NNiaHSd x Brown Norway/BiNia (F344xBN) rat model. The NIA has recommended the F344xBN due to its longer maximal life span, higher age for 50% mortality, and the fact that it exhibits a normal distribution of age-related pathologies at later ages [10, 11]. Here, we investigated the effects of aging on cardiovascular structure and function in the adult, aged, and very aged female F344xBN rats. Compared to adult hearts, increased age was associated with increases in oxidative-nitrosative stress, oxidative damage, (increases in hydroethidine (HE) staining, 4-hydroxynonenal (4-HNE), and nitrotyrosine expression), and activation of the mitochondrial-mediated apoptosis pathway (increased number of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive nuclei, increased activation of caspases, and Bax/Bcl-2 ratio). Age related changes in cardiac structure consisted of an increase in heart to body weight ratio, cardiomyocyte cross sectional area (CSA), posterior wall thickening, and left ventricle chamber dilatation. Coincident with these changes in cardiac structure and signaling, we also found that increased age was associated with evidence of diastolic dysfunction, alterations in heart rhythm intervals, and alterations in connexin 43 (Cx43) expression. The incidence of arrhythmias was not different with age; however, valvular dysfunction was increased. In the female F344xBN aorta there was an age-associated increase of intima-medial thickness and activation of p44/42 MAPK. Taken together, these results suggest that the female F344xBN rat may be an appropriate cardiovascular aging female rodent model in the absence of pathologies

Effect of aging on cellular mechanotransduction

Aging is becoming a critical heath care issue and a burgeoning economic burden on society. Mechanotransduction is the ability of the cell to sense, process, and respond to mechanical stimuli and is an important regulator of physiologic function that has been found to play a role in regulating gene expression, protein synthesis, cell differentiation, tissue growth, and most recently, the pathophysiology of disease. Here we will review some of the recent findings of this field and attempt, where possible, to present changes in mechanotransduction that are associated with the aging process in several selected physiological systems, including musculoskeletal, cardiovascular, neuronal, respiratory systems and skin

Cellular Senescence and Their Role in Liver Metabolism in Health and Disease: Overview and Future Directions

Chronic liver disease has globally risen mainly due to a prevalent hepatitis C virus (HCV) infection rate and an epidemic of obesity. It is estimated by the year 2030, 2.2 billion people around the world will be overweight and 1.1 billion people will be obese. Diabetes and obesity are the main risk factors for the development of the metabolic syndrome and in the liver of non-alcoholic fatty liver disease (NAFLD) which could progress to non-alcoholic fatty steatohepatitis (NASH) related cirrhosis and liver malignancy. At present there is not effective therapy for NASH besides loss of weight and exercise. Furthermore, optimal management of HCC with curative intent includes resection or liver transplantation. Nevertheless, these therapies are limited because the degree of liver dysfunction or the medical conditions at the time of diagnosis and the scarcity of available liver grafts. The role of cellular lipid management and metabolism in human health and disease is taking a center stage. The present overview articulates the current pathophysiology of fatty liver disease under the aging processes, potential biological markers of liver disease diagnosis and progression and future therapies

Acetaminophen Improves Protein Translational Signaling in Aged Skeletal Muscle

Background: Age-related muscle atrophy is characterized by increased oxidative stress, diminished Akt enzymatic function, and reduced phosphorylation of the mammalian target of rapamycin (mTOR), which can be attenuated by chronic acetaminophen ingestion. Here we hypothesize that age-related impairments in Akt/ mTOR function are associated with reduced protein translational signaling, and that these changes, if present, can be attenuated by acetaminophen treatment. Results: Compared to 6- and 27-month old animals, the expression of the mTOR-complex proteins raptor and GbL and the phosphorylation of tuberin/TSC2 (Thr1462) were reduced in the soleus muscles of very aged rats (33 months old). These changes in Akt/mTOR pathway signaling proteins were in turn associated with decreased phosphorylation of S6 kinase p85S6K (Thr412) and eukaryotic translation initiation factor-4E (eIF4E) binding protein-1 (4EBP1, Thr37/46), reduced phosphorylation of S6 ribosomal protein (Ser235/236), and increased inhibition of eIF4E by binding to 4EBP1. Age-associated alterations in the Akt/mTOR pathway signaling and in the phosphorylation of the stress-responsive eIF2a protein were attenuated by chronic acetaminophen treatment (30 mg/kg body weight per day). Ex vivo incubation of adult muscles with hydrogen peroxide mimicked the age-related decreases seen in eIF4E and 4EBP1 phosphorylation, whereas the inclusion of acetaminophen in the muscle bath attenuated this effect. Conclusion: Aging is associated with impairments in the regulation of proteins thought to be important in controlling mRNA translation, and acetaminophen may be useful for the treatment of age-related muscle atrophy by reducing oxidative stress

Aging-Associated Dysfunction of Akt/Protein Kinase B: S-Nitrosylation and Acetaminophen Intervention

Background: Aged skeletal muscle is characterized by an increased incidence of metabolic and functional disorders, which if allowed to proceed unchecked can lead to increased morbidity and mortality. The mechanism(s) underlying the development of these disorders in aging skeletal muscle are not well understood. Protein kinase B (Akt/PKB) is an important regulator of cellular metabolism and survival, but it is unclear if aged muscle exhibits alterations in Akt function. Here we report a novel dysfunction of Akt in aging muscle, which may relate to S-nitrosylation and can be prevented by acetaminophen intervention. Principal Findings: Compared to 6- and 27-month rats, the phosphorylation of Akt (Ser473 and Thr308) was higher in soleus muscles of very aged rats (33-months). Paradoxically, these increases in Akt phosphorylation were associated with diminished mammalian target of rapamycin (mTOR) phosphorylation, along with decreased levels of insulin receptor beta (IR-b), phosphoinositide 3-kinase (PI3K), phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and phosphorylation of phosphoinositide-dependent kinase-1 (PDK1) (Ser241). In vitro Akt kinase measurements and ex vivo muscle incubation experiments demonstrated age-related impairments of Akt kinase activity, which were associated with increases in Akt S-nitrosylation and inducible nitric oxide synthase (iNOS). Impairments in Akt function occurred parallel to increases in myocyte apoptosis and decreases in myocyte size and the expression of myosin and actin. These age-related disorders were attenuated by treating aged (27-month) animals with acetaminophen (30 mg/kg body weight/day) for 6- months. Conclusions: These data demonstrate that Akt dysfunction and increased S-nitrosylation of Akt may contribute to ageassociated disorders in skeletal muscle and that acetaminophen may be efficacious for the treatment of age-related muscle dysfunction

Age-associated alterations of cardiac structure and function in the female F344xBN rat heart

The Fischer 344/NNiaHSD × Brown Norway/BiNia F1 (F344xBN) rat model exhibits an increased life span and fewer age-associated pathologies compared to commonly used Fischer 344 (F344). How aging may affect cardiac structure and function in these animals, has to our knowledge, not been investigated. Echocardiography was performed on female F344xBN rats at 6, 26, and 30 months of age using a Phillips 5500 Echocardiography system. Before sacrifice, electrocardiograms were measured in the female F344xBN in order to determine heart rhythm interval changes. Aging was associated with an increase in heart to body weight ratio, cardiomyocyte cross-sectional area, posterior wall thickening, and left ventricle chamber dilatation. Aging was associated with slight evidence of diastolic dysfunction. Alterations in heart rhythm intervals were associated with alterations in the spatial distribution of connexin 43. The incidence of arrhythmias was not different with age; however, valvular dysfunction was increased. These data suggest that aging in the female F344xBN rat heart is associated with changes in cardiac structure as well as function. Further investigation regarding other parameters of cardiac biochemistry and function is needed to better understand the normal compensated cardiovascular aging process in the female F344xBN

Impaired overload-induced hypertrophy is associated with diminished mTOR signaling in insulin-resistant skeletal muscle of the obese Zucker rat

Recent data have suggested that insulin resistance may be associated with a diminished ability of skeletal muscle to undergo hypertrophy (Paturi S, Gutta AK, Kakarla SK, Katta A, Arnold EC, Wu M, Rice KM, Blough ER. J Appl Physiol 108: 7–13, 2010). Here we examine the effects of insulin resistance using the obese Zucker (OZ) rat with increased muscle loading on the regulation of the mammalian target of rapamycin (mTOR) and its downstream signaling intermediates 70-kDa ribosomal protein S6 kinase (p70S6k), ribosomal protein S6 (rpS6), eukaryotic elongation factor 2 (eEF2), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). Compared with that observed in lean Zucker (LZ) rats, the degree of soleus muscle hypertrophy as assessed by changes in muscle wet weight (LZ: 35% vs. OZ: 16%) was significantly less in the OZ rats after 3 wk of muscle overload (P < 0.05). This diminished growth in the OZ rats was accompanied by significant impairments in the ability of the soleus to undergo phosphorylation of mTOR (Ser2448), p70S6k (Thr389), rpS6 (Ser235/236), and protein kinase B (Akt) (Ser473 and Thr308) (P < 0.05). Taken together, these data suggest that impaired overload-induced hypertrophy in insulin-resistant skeletal muscle may be related to decreases in the ability of the muscle to undergo mTOR-related signaling

Aging-associated dysfunction of Akt/protein kinase B: S-nitrosylation and acetaminophen intervention.

BACKGROUND:Aged skeletal muscle is characterized by an increased incidence of metabolic and functional disorders, which if allowed to proceed unchecked can lead to increased morbidity and mortality. The mechanism(s) underlying the development of these disorders in aging skeletal muscle are not well understood. Protein kinase B (Akt/PKB) is an important regulator of cellular metabolism and survival, but it is unclear if aged muscle exhibits alterations in Akt function. Here we report a novel dysfunction of Akt in aging muscle, which may relate to S-nitrosylation and can be prevented by acetaminophen intervention. PRINCIPAL FINDINGS:Compared to 6- and 27-month rats, the phosphorylation of Akt (Ser473 and Thr308) was higher in soleus muscles of very aged rats (33-months). Paradoxically, these increases in Akt phosphorylation were associated with diminished mammalian target of rapamycin (mTOR) phosphorylation, along with decreased levels of insulin receptor beta (IR-beta), phosphoinositide 3-kinase (PI3K), phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and phosphorylation of phosphoinositide-dependent kinase-1 (PDK1) (Ser241). In vitro Akt kinase measurements and ex vivo muscle incubation experiments demonstrated age-related impairments of Akt kinase activity, which were associated with increases in Akt S-nitrosylation and inducible nitric oxide synthase (iNOS). Impairments in Akt function occurred parallel to increases in myocyte apoptosis and decreases in myocyte size and the expression of myosin and actin. These age-related disorders were attenuated by treating aged (27-month) animals with acetaminophen (30 mg/kg body weight/day) for 6-months. CONCLUSIONS:These data demonstrate that Akt dysfunction and increased S-nitrosylation of Akt may contribute to age-associated disorders in skeletal muscle and that acetaminophen may be efficacious for the treatment of age-related muscle dysfunction

Iron-Induced Cardiac Damage: Role of Apoptosis and Deferasirox Intervention

Excess cardiac iron levels are associated with cardiac damage and can result in increased morbidity and mortality. Here, we hypothesize that elevations in tissue iron can activate caspase-dependent signaling, which leads to increased cardiac apoptosis and fibrosis, and that these alterations can be attenuated by iron chelation. Using an iron-overloaded gerbil model, we show that increased cardiac iron is associated with reduced activation of Akt (Ser473 and Thr308), diminished phosphorylation of the proapoptotic regulator Bad (Ser136), and an increased Bax/Bcl-2 ratio. These iron-overload-induced alterations in Akt/Bad phosphorylation and Bax/Bcl-2 ratio were coupled with increased activation of the downstream caspase-9 (40/38- and 17-kDa fragments) and apoptosis executioner caspase-3 (19- and 17-kDa fragments), which were accompanied by evidence of elevated cytoskeletal α-fodrin cleavage (150- and 120-kDa fragments), discontinuity of myocardial membrane dystrophin immunoreactivity, increases in the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells (nucleic DNA fragmentation), and cardiac fibrosis. We demonstrate that the administration of deferasirox, a tridentate iron chelator, is associated with diminished tissue iron deposition, attenuated activation of caspases, reduced α-fodrin cleavage, improved membrane integrity, decreased TUNEL reactivity, and attenuated cardiac fibrosis. These results suggest that the activation of caspase-dependent signaling may play a role in the development of iron-induced cardiac apoptosis and fibrosis, and deferasirox, via a reduction in cardiac tissue iron levels, may be useful for decreasing the extent of iron-induced cardiac damage