Wistar rat as an animal model to study high-fat induced kidney damage: a systematic review

The effects of high-fat-associated kidney damage in humans are not completely elucidated. Animal experiments are essential to understanding the mechanisms underlying human diseases. This systematic review aimed to compile evidence of the role of a high-fat diet during the development of renal lipotoxicity and fibrosis of Wistar rats to understand whether this is a satisfactory model for the study of high fat-induced kidney damage. We conducted systematic searches in PUBMED, EMBASE, Lilacs, and Web of Science databases from inception until May 2021. The risk of bias was assessed using SYRCLE toll. Two reviewers independently screened abstracts and reviewed full-text articles. A total of 11 studies were included. The damage varied depending on the age and sex of the animals, time of protocol, and amount of fat in the diet. In conclusion, the Wistar rat is an adequate animal model to assess the effects of a high-fat diet on the kidneys.HighlightsA high-fat diet may promote kidney damage in Wistar rats.Wistar rat is efficient as an animal model to study high-fat-induced kidney damage.The effect of the diet depends on the fat amount, consumption time, and animal age.

ATF4-dependent increase in mitochondrial-endoplasmic reticulum tethering following OPA1 deletion in skeletal muscle

Mitochondria and endoplasmic reticulum (ER) contact sites (MERCs) are protein- and lipid-enriched hubs that mediate interorganellar communication by contributing to the dynamic transfer of Ca2+, lipid, and other metabolites between these organelles. Defective MERCs are associated with cellular oxidative stress, neurodegenerative disease, and cardiac and skeletal muscle pathology via mechanisms that are poorly understood. We previously demonstrated that skeletal muscle-specific knockdown (KD) of the mitochondrial fusion mediator optic atrophy 1 (OPA1) induced ER stress and correlated with an induction of Mitofusin-2, a known MERC protein. In the present study, we tested the hypothesis that Opa1 downregulation in skeletal muscle cells alters MERC formation by evaluating multiple myocyte systems, including from mice and Drosophila, and in primary myotubes. Our results revealed that OPA1 deficiency induced tighter and more frequent MERCs in concert with a greater abundance of MERC proteins involved in calcium exchange. Additionally, loss of OPA1 increased the expression of activating transcription factor 4 (ATF4), an integrated stress response (ISR) pathway effector. Reducing Atf4 expression prevented the OPA1-loss-induced tightening of MERC structures. OPA1 reduction was associated with decreased mitochondrial and sarcoplasmic reticulum, a specialized form of ER, calcium, which was reversed following ATF4 repression. These data suggest that mitochondrial stress, induced by OPA1 deficiency, regulates skeletal muscle MERC formation in an ATF4-dependent manner.

Mitochondrial Dynamics, Diabetes, and Cardiovascular Disease

Mitochondria undergo repeated cycles of fusion and fission that regulate their size and shape by a process known as mitochondrial dynamics. Numerous studies have revealed the importance of this process in maintaining mitochondrial health and cellular homeostasis, particularly in highly metabolically active tissues such as skeletal muscle and the heart. Here, we review the literature on the relationship between mitochondrial dynamics and the pathophysiology of type 2 diabetes and cardiovascular disease (CVD). Importantly, we emphasize divergent outcomes resulting from downregulating distinct mitochondrial dynamics proteins in various tissues. This review underscores compensatory mechanisms and adaptive pathways that offset potentially detrimental effects, resulting instead in improved metabolic health. Finally, we offer a perspective on potential therapeutic implications of modulating mitochondrial dynamics proteins for treatment of diabetes and CVD.

ARTICLE HIGHLIGHTS

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

Effect of Low-Dose Progesterone on Glycemic Metabolism, Morphology and Function of Adipose Tissue and Pancreatic Islets in Diet-Induced Obese Female Mice

BACKGROUND

Obesity is a worldwide concern due to its global rapid expansion and remarkable impact on individual's health by predisposing to several other diseases. About twice as many women as men suffer from severe obesity and, in fact, there are stages in a woman's life when weight gain and adiposity can result in greater damage to health. For example, obesity triples the chance of a woman developing gestational diabetes. Many hormones promote the metabolic adaptations of pregnancy, including progesterone, whose role in female obesity is still not well known despite being involved in many physiological and pathological processes.

METHODS

Here we investigated whether progesterone treatment at low dose can worsen the glucose metabolism and the morpho functional aspects of adipose tissue and pancreas in obese females. Mice were assigned into four groups: normocaloric diet control (NO-CO), high-fat and -fructose diet control (HFF-CO), normocaloric diet plus progesterone (NO-PG) and high-fat and -fructose diet plus progesterone (HFF-PG) for 10 weeks. Infusion of progesterone (0.25 mg/kg/day) was done by osmotic minipump in the last 21 days of protocol.

RESULTS

Animals fed a hypercaloric diet exhibited obesity with increased body weight (p < 0.0001), adipocyte hypertrophy (p < 0.0001), hyperglycemia (p = 0.03), and glucose intolerance (p = 0.001). HFF-CO and HFF-PG groups showed lower adiponectin concentration (p < 0.0001) and glucose-stimulated insulin secretion (p = 0.03), without differences in islet size. Progesterone attenuated glucose intolerance in the HFF-PG group (p = 0.03), however, did not change morphology or endocrine function of adipose tissue and pancreatic islets.

CONCLUSIONS

Taken together, our results showed that low dose of progesterone does not worsen the effects of hypercaloric diet in glycemic metabolism, morphology and function of adipose tissue and pancreatic islets in female animals. These results may improve the understanding of the mechanisms underlying the pathogenesis of obesity in women and eventually open new avenues for therapeutic strategies and better comprehension of the interactions between progesterone effects and obesity.

GDF15 is required for cold-induced thermogenesis and contributes to improved systemic metabolic health following loss of OPA1 in brown adipocytes

We previously reported that mice lacking the protein optic atrophy 1 (OPA1 BKO) in brown adipose tissue (BAT) display induction of the activating transcription factor 4 (ATF4), which promotes fibroblast growth factor 21 (FGF21) secretion as a batokine. FGF21 increases metabolic rates under baseline conditions but is dispensable for the resistance to diet-induced obesity (DIO) reported in OPA1 BKO mice (Pereira et al., 2021). To determine alternative mediators of this phenotype, we performed transcriptome analysis, which revealed increased levels of growth differentiation factor 15 (GDF15), along with increased protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) levels in BAT. To investigate whether ATF4 induction was mediated by PERK and evaluate the contribution of GDF15 to the resistance to DIO, we selectively deleted PERK or GDF15 in OPA1 BKO mice. Mice with reduced OPA1 and PERK levels in BAT had preserved ISR activation. Importantly, simultaneous deletion of OPA1 and GDF15 partially reversed the resistance to DIO and abrogated the improvements in glucose tolerance. Furthermore, GDF15 was required to improve cold-induced thermogenesis in OPA1 BKO mice. Taken together, our data indicate that PERK is dispensable to induce the ISR, but GDF15 contributes to the resistance to DIO, and is required for glucose homeostasis and thermoregulation in OPA1 BKO mice by increasing energy expenditure.

A Comprehensive Approach to Sample Preparation for Electron Microscopy and the Assessment of Mitochondrial Morphology in Tissue and Cultured Cells

Mitochondria respond to metabolic demands of the cell and to incremental damage, in part, through dynamic structural changes that include fission (fragmentation), fusion (merging of distinct mitochondria), autophagic degradation (mitophagy), and biogenic interactions with the endoplasmic reticulum (ER). High resolution study of mitochondrial structural and functional relationships requires rapid preservation of specimens to reduce technical artifacts coupled with quantitative assessment of mitochondrial architecture. A practical approach for assessing mitochondrial fine structure using two dimensional and three dimensional high-resolution electron microscopy is presented, and a systematic approach to measure mitochondrial architecture, including volume, length, hyperbranching, cristae morphology, and the number and extent of interaction with the ER is described. These methods are used to assess mitochondrial architecture in cells and tissue with high energy demand, including skeletal muscle cells, mouse brain tissue, and Drosophila muscles. The accuracy of assessment is validated in cells and tissue with deletion of genes involved in mitochondrial dynamics.

The roles of FGF21 and GDF15 in mediating the mitochondrial integrated stress response

Various models of mitochondrial stress result in induction of the stress-responsive cytokines fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15). This is an adaptive mechanism downstream of the mitochondrial integrated stress response frequently associated with improvements in systemic metabolic health. Both FGF21 and GDF15 have been shown to modulate energy balance and glucose homeostasis, and their pharmacological administration leads to promising beneficial effects against obesity and associated metabolic diseases in pre-clinical models. Furthermore, endogenous upregulation of FGF21 and GDF15 is associated with resistance to diet-induced obesity (DIO), improved glucose homeostasis and increased insulin sensitivity. In this review, we highlight several studies on transgenic mouse models of mitochondrial stress and will compare the specific roles played by FGF21 and GDF15 on the systemic metabolic adaptations reported in these models.

ATF4 Expression in Thermogenic Adipocytes is Required for Cold-Induced Thermogenesis in Mice via FGF21-Independent Mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially via upregulation of FGF21. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis by generating mice selectively lacking either Atf4 ( ATF4 BKO ) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum -fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue (WAT). Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum -fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis by activating amino acid metabolism in BAT in a FGF21-independent manner.

Systematic Transmission Electron Microscopy-Based Identification and 3D Reconstruction of Cellular Degradation Machinery

Various intracellular degradation organelles, including autophagosomes, lysosomes, and endosomes, work in tandem to perform autophagy, which is crucial for cellular homeostasis. Altered autophagy contributes to the pathophysiology of various diseases, including cancers and metabolic diseases. This paper aims to describe an approach to reproducibly identify and distinguish subcellular structures involved in macroautophagy. Methods are provided that help avoid common pitfalls. How to distinguish between lysosomes, lipid droplets, autolysosomes, autophagosomes, and inclusion bodies are also discussed. These methods use transmission electron microscopy (TEM), which is able to generate nanometer-scale micrographs of cellular degradation components in a fixed sample. Serial block face-scanning electron microscopy is also used to visualize the 3D morphology of degradation machinery using the Amira software. In addition to TEM and 3D reconstruction, other imaging techniques are discussed, such as immunofluorescence and immunogold labeling, which can be used to classify cellular organelles, reliably and accurately. Results show how these methods may be used to accurately quantify cellular degradation machinery under various conditions, such as treatment with the endoplasmic reticulum stressor thapsigargin or ablation of the dynamin-related protein 1.

Correction: Garza-Lopez et al. Protocols for Generating Surfaces and Measuring 3D Organelle Morphology Using Amira. Cells 2022, 11, 65

In the original publication [...].

OPA1 Regulates Lipid Metabolism and Cold-Induced Browning of White Adipose Tissue in Mice

Mitochondria play a vital role in white adipose tissue (WAT) homeostasis including adipogenesis, fatty acid synthesis, and lipolysis. We recently reported that the mitochondrial fusion protein optic atrophy 1 (OPA1) is required for induction of fatty acid oxidation and thermogenic activation in brown adipocytes. In the current study we investigated the role of OPA1 in WAT function in vivo. We generated mice with constitutive or inducible knockout of OPA1 selectively in adipocytes. Studies were conducted under baseline conditions, at thermoneutrality, following high-fat feeding or during cold exposure. OPA1 deficiency reduced mitochondrial respiratory capacity in white adipocytes, impaired lipolytic signaling, repressed expression of de novo lipogenesis and triglyceride synthesis pathways, and promoted adipose tissue senescence and inflammation. Reduced WAT mass was associated with hepatic triglycerides accumulation and glucose intolerance. Moreover, mice deficient for OPA1 in adipocytes had impaired adaptive thermogenesis and reduced cold-induced browning of subcutaneous WAT and were completely resistant to diet-induced obesity. In conclusion, OPA1 expression and function in adipocytes are essential for adipose tissue expansion, lipid biosynthesis, and fatty acid mobilization of WAT and brown adipocytes and for thermogenic activation of brown and beige adipocytes.

Protocols for Generating Surfaces and Measuring 3D Organelle Morphology Using Amira

High-resolution 3D images of organelles are of paramount importance in cellular biology. Although light microscopy and transmission electron microscopy (TEM) have provided the standard for imaging cellular structures, they cannot provide 3D images. However, recent technological advances such as serial block-face scanning electron microscopy (SBF-SEM) and focused ion beam scanning electron microscopy (FIB-SEM) provide the tools to create 3D images for the ultrastructural analysis of organelles. Here, we describe a standardized protocol using the visualization software, Amira, to quantify organelle morphologies in 3D, thereby providing accurate and reproducible measurements of these cellular substructures. We demonstrate applications of SBF-SEM and Amira to quantify mitochondria and endoplasmic reticulum (ER) structures.

Skeletal muscle type-specific mitochondrial adaptation to high-fat diet relies on differential autophagy modulation

In obesity, skeletal muscle mitochondrial activity changes to cope with increased nutrient availability. Autophagy has been proposed as an essential mechanism involved in the regulation of mitochondrial metabolism. Still, the contribution of autophagy to mitochondrial adaptations in skeletal muscle during obesity is unknown. Here, we show that in response to high-fat diet (HFD) feeding, distinct skeletal muscles in mice exhibit differentially regulated autophagy that may modulate mitochondrial activity. We observed that after 4 and 40 weeks of high-fat diet feeding, OXPHOS subunits and mitochondrial DNA content increased in the oxidative soleus muscle. However, in gastrocnemius muscle, which has a mixed fiber-type composition, the mitochondrial mass increased only after 40 weeks of HFD feeding. Interestingly, fatty acid-supported mitochondrial respiration was enhanced in gastrocnemius, but not in soleus muscle after a 4-week HFD feeding. This increased metabolic profile in gastrocnemius was paralleled by preserving autophagy flux, while autophagy flux in soleus was reduced. To determine the role of autophagy in this differential response, we used an autophagy-deficient mouse model with partial deletion of Atg7 specifically in skeletal muscle (SkM-Atg7+/- mice). We observed that Atg7 reduction resulted in diminished autophagic flux in skeletal muscle, alongside blunting the HFD-induced increase in fatty acid-supported mitochondrial respiration observed in gastrocnemius. Remarkably, SkM-Atg7+/- mice did not present increased mitochondria accumulation. Altogether, our results show that HFD triggers specific mitochondrial adaptations in skeletal muscles with different fiber type compositions, and that Atg7-mediated autophagy modulates mitochondrial respiratory capacity but not its content in response to an obesogenic diet.

A Universal Approach to Analyzing Transmission Electron Microscopy with ImageJ

Transmission electron microscopy (TEM) is widely used as an imaging modality to provide high-resolution details of subcellular components within cells and tissues. Mitochondria and endoplasmic reticulum (ER) are organelles of particular interest to those investigating metabolic disorders. A straightforward method for quantifying and characterizing particular aspects of these organelles would be a useful tool. In this protocol, we outline how to accurately assess the morphology of these important subcellular structures using open source software ImageJ, originally developed by the National Institutes of Health (NIH). Specifically, we detail how to obtain mitochondrial length, width, area, and circularity, in addition to assessing cristae morphology and measuring mito/endoplasmic reticulum (ER) interactions. These procedures provide useful tools for quantifying and characterizing key features of sub-cellular morphology, leading to accurate and reproducible measurements and visualizations of mitochondria and ER.

OPA1 deletion in brown adipose tissue improves thermoregulation and systemic metabolism via FGF21

Adrenergic stimulation of brown adipocytes alters mitochondrial dynamics, including the mitochondrial fusion protein optic atrophy 1 (OPA1). However, direct mechanisms linking OPA1 to brown adipose tissue (BAT) physiology are incompletely understood. We utilized a mouse model of selective OPA1 deletion in BAT (OPA1 BAT KO) to investigate the role of OPA1 in thermogenesis. OPA1 is required for cold-induced activation of thermogenic genes in BAT. Unexpectedly, OPA1 deficiency induced fibroblast growth factor 21 (FGF21) as a BATokine in an activating transcription factor 4 (ATF4)-dependent manner. BAT-derived FGF21 mediates an adaptive response by inducing browning of white adipose tissue, increasing resting metabolic rates, and improving thermoregulation. However, mechanisms independent of FGF21, but dependent on ATF4 induction, promote resistance to diet-induced obesity in OPA1 BAT KO mice. These findings uncover a homeostatic mechanism of BAT-mediated metabolic protection governed in part by an ATF4-FGF21 axis, which is activated independently of BAT thermogenic function.

Aerobic Physical Exercise Improves Exercise Tolerance and Fasting Glycemia Independent of Body Weight Change in Obese Females

Obesity is associated with increased risk of several chronic diseases and the loss of disease-free years, which has increased the focus of much research for the discovery of therapy to combat it. Under healthy conditions, women tend to store more fat in subcutaneous deposits. However, this sexual dimorphism tends to be lost in the presence of comorbidities, such as type 2 diabetes mellitus (T2DM). Aerobic physical exercise (APE) has been applied in the management of obesity, however, is still necessary to better understand the effects of APE in obese female. Thus, we investigated the effect of APE on body weight, adiposity, exercise tolerance and glucose metabolism in female ob/ob mice. Eight-weeks-old female wild-type C57BL/6J and leptin-deficient ob/ob mice (Lep^ob) were distributed into three groups: wild-type sedentary group (Wt; n = 6), leptin-deficient sedentary group (Lep^obS; n = 5) and leptin-deficient trained group (Lep^obT; n = 8). The Lep^obT mice were subjected to 8 weeks of aerobic physical exercise (APE) at 60% of the maximum velocity achieved in the running capacity test. The APE had no effect in attenuating body weight gain, and did not reduce subcutaneous and retroperitoneal white adipose tissue (SC-WAT and RP-WAT, respectively) and interscapular brown adipose tissue (iBAT) weights. The APE neither improved glucose intolerance nor insulin resistance in the Lep^obT group. Also, the APE did not reduce the diameter or the area of RP-WAT adipocytes, but the APE reduced the diameter and the area of SC-WAT adipocytes, which was associated with lower fasting glycemia and islet/pancreas area ratio in the Lep^obT group. In addition, the APE increased exercise tolerance and this response was also associated with lower fasting glycemia in the Lep^obT group. In conclusion, starting APE at a later age with a more severe degree of obesity did not attenuate the excessive body weight gain, however the APE promoted benefits that can improve the female health, and for this reason it should be recommended as a non-pharmacological therapy for obesity.

Maintaining Myocardial Glucose Utilization in Diabetic Cardiomyopathy Accelerates Mitochondrial Dysfunction

Cardiac glucose uptake and oxidation are reduced in diabetes despite hyperglycemia. Mitochondrial dysfunction contributes to heart failure in diabetes. It is unclear whether these changes are adaptive or maladaptive. To directly evaluate the relationship between glucose delivery and mitochondrial dysfunction in diabetic cardiomyopathy, we generated transgenic mice with inducible cardiomyocyte-specific expression of the GLUT4. We examined mice rendered hyperglycemic following low-dose streptozotocin prior to increasing cardiomyocyte glucose uptake by transgene induction. Enhanced myocardial glucose in nondiabetic mice decreased mitochondrial ATP generation and was associated with echocardiographic evidence of diastolic dysfunction. Increasing myocardial glucose delivery after short-term diabetes onset exacerbated mitochondrial oxidative dysfunction. Transcriptomic analysis revealed that the largest changes, driven by glucose and diabetes, were in genes involved in mitochondrial function. This glucose-dependent transcriptional repression was in part mediated by O-GlcNAcylation of the transcription factor Sp1. Increased glucose uptake induced direct O-GlcNAcylation of many electron transport chain subunits and other mitochondrial proteins. These findings identify mitochondria as a major target of glucotoxicity. They also suggest that reduced glucose utilization in diabetic cardiomyopathy might defend against glucotoxicity and caution that restoring glucose delivery to the heart in the context of diabetes could accelerate mitochondrial dysfunction by disrupting protective metabolic adaptations.

Post-weaning Exposure to High-Fat Diet Induces Kidney Lipid Accumulation and Function Impairment in Adult Rats

Aim: We investigated the kidney morphofunctional consequences of high-fat diet intake since post-weaning in adult rats.

Main Methods: Male Wistar rats were divided into two groups: ND (normal diet; n = 10) and HD (high-fat diet; n = 10). The high-fat diet was introduced post-weaned and animals were followed for 8 weeks.

Key Findings: HD group did not change body weight gain even though food consumption has decreased with no changes in caloric consumption. The HD group showed glucose intolerance and insulin resistance. The glomerular filtration rate (GFR) was decreased in vivo (ND: 2.8 ± 1.01; HD: 1.1 ± 0.14 ml/min) and in the isolated perfusion method (34% of decrease). Renal histological analysis showed a retraction in glomeruli and an increase in kidney lipid deposition (ND: 1.5 ± 0.17 HD: 5.9 ± 0.06%). Furthermore, the high-fat diet consumption increased the pro-inflammatory cytokines IL-6 (ND: 1,276 ± 203; HD: 1,982 ± 47 pg/mL/mg) and IL-1b (ND: 97 ± 12 HD: 133 ± 5 pg/mL/mg) without changing anti-inflammatory cytokine IL-10.

Significance: Our study provides evidence that high-fat diet consumption leads to renal lipid accumulation, increases inflammatory cytokines, induces glomeruli retraction, and renal dysfunction. These damages observed in the kidney could be associated with an increased risk to advanced CKD in adulthood suggesting that reduction of high-fat ingestion during an early period of life can prevent metabolic disturbances and renal lipotoxicity.

Mitochondrial Reactive Oxygen Species in Lipotoxic Hearts Induce Post-Translational Modifications of AKAP121, DRP1, and OPA1 That Promote Mitochondrial Fission

RATIONALE

Cardiac lipotoxicity, characterized by increased uptake, oxidation, and accumulation of lipid intermediates, contributes to cardiac dysfunction in obesity and diabetes mellitus. However, mechanisms linking lipid overload and mitochondrial dysfunction are incompletely understood.

OBJECTIVE

To elucidate the mechanisms for mitochondrial adaptations to lipid overload in postnatal hearts in vivo.

METHODS AND RESULTS

Using a transgenic mouse model of cardiac lipotoxicity overexpressing ACSL1 (long-chain acyl-CoA synthetase 1) in cardiomyocytes, we show that modestly increased myocardial fatty acid uptake leads to mitochondrial structural remodeling with significant reduction in minimum diameter. This is associated with increased palmitoyl-carnitine oxidation and increased reactive oxygen species (ROS) generation in isolated mitochondria. Mitochondrial morphological changes and elevated ROS generation are also observed in palmitate-treated neonatal rat ventricular cardiomyocytes. Palmitate exposure to neonatal rat ventricular cardiomyocytes initially activates mitochondrial respiration, coupled with increased mitochondrial polarization and ATP synthesis. However, long-term exposure to palmitate (>8 hours) enhances ROS generation, which is accompanied by loss of the mitochondrial reticulum and a pattern suggesting increased mitochondrial fission. Mechanistically, lipid-induced changes in mitochondrial redox status increased mitochondrial fission by increased ubiquitination of AKAP121 (A-kinase anchor protein 121) leading to reduced phosphorylation of DRP1 (dynamin-related protein 1) at Ser637 and altered proteolytic processing of OPA1 (optic atrophy 1). Scavenging mitochondrial ROS restored mitochondrial morphology in vivo and in vitro.

CONCLUSIONS

Our results reveal a molecular mechanism by which lipid overload-induced mitochondrial ROS generation causes mitochondrial dysfunction by inducing post-translational modifications of mitochondrial proteins that regulate mitochondrial dynamics. These findings provide a novel mechanism for mitochondrial dysfunction in lipotoxic cardiomyopathy.

Insulin and IGF-1 receptors regulate FoxO-mediated signaling in muscle proteostasis

Diabetes strongly impacts protein metabolism, particularly in skeletal muscle. Insulin and IGF-1 enhance muscle protein synthesis through their receptors, but the relative roles of each in muscle proteostasis have not been fully elucidated. Using mice with muscle-specific deletion of the insulin receptor (M-IR-/- mice), the IGF-1 receptor (M-IGF1R-/- mice), or both (MIGIRKO mice), we assessed the relative contributions of IR and IGF1R signaling to muscle proteostasis. In differentiated muscle, IR expression predominated over IGF1R expression, and correspondingly, M-IR-/- mice displayed a moderate reduction in muscle mass whereas M-IGF1R-/- mice did not. However, these receptors serve complementary roles, such that double-knockout MIGIRKO mice displayed a marked reduction in muscle mass that was linked to increases in proteasomal and autophagy-lysosomal degradation, accompanied by a high-protein-turnover state. Combined muscle-specific deletion of FoxO1, FoxO3, and FoxO4 in MIGIRKO mice reversed increased autophagy and completely rescued muscle mass without changing proteasomal activity. These data indicate that signaling via IR is more important than IGF1R in controlling proteostasis in differentiated muscle. Nonetheless, the overlap of IR and IGF1R signaling is critical to the regulation of muscle protein turnover, and this regulation depends on suppression of FoxO-regulated, autophagy-mediated protein degradation.

Maintaining PGC-1α expression following pressure overload-induced cardiac hypertrophy preserves angiogenesis but not contractile or mitochondrial function

During pathological hypertrophy, peroxisome proliferator-activated receptor coactivator 1α (PGC-1α) is repressed in concert with reduced mitochondrial oxidative capacity and fatty acid oxidation (FAO). We therefore sought to determine if maintaining or increasing PGC-1α levels in the context of pressure overload hypertrophy (POH) would preserve mitochondrial function and prevent contractile dysfunction. Pathological cardiac hypertrophy was induced using 4 wk of transverse aortic constriction (TAC) in mice overexpressing the human PGC-1α genomic locus via a bacterial artificial chromosome (TG) and nontransgenic controls (Cont). PGC-1α levels were increased by 40% in TG mice and were sustained following TAC. Although TAC-induced repression of FAO genes and oxidative phosphorylation (oxphos) genes was prevented in TG mice, mitochondrial function and ATP synthesis were equivalently impaired in Cont and TG mice after TAC. Contractile function was also equally impaired in Cont and TG mice following TAC, as demonstrated by decreased +dP/dt and ejection fraction and increased left ventricular developed pressure and end diastolic pressure. Conversely, capillary density was preserved, in concert with increased VEGF expression, while apoptosis and fibrosis were reduced in TG relative to Cont mice after TAC. Hence, sustaining physiological levels of PGC-1α expression following POH, while preserving myocardial vascularity, does not prevent mitochondrial and contractile dysfunction.

GLUT1 deficiency in cardiomyocytes does not accelerate the transition from compensated hypertrophy to heart failure

The aim of this study was to determine whether endogenous GLUT1 induction and the increased glucose utilization that accompanies pressure overload hypertrophy (POH) are required to maintain cardiac function during hemodynamic stress, and to test the hypothesis that lack of GLUT1 will accelerate the transition to heart failure. To determine the contribution of endogenous GLUT1 to the cardiac adaptation to POH, male mice with cardiomyocyte-restricted deletion of the GLUT1 gene (G1KO) and their littermate controls (Cont) were subjected to transverse aortic constriction (TAC). GLUT1 deficiency reduced glycolysis and glucose oxidation by 50%, which was associated with a reciprocal increase in fatty acid oxidation (FAO) relative to controls. Four weeks after TAC, glycolysis increased and FAO decreased by 50% in controls, but were unchanged in G1KO hearts relative to shams. G1KO and controls exhibited equivalent degrees of cardiac hypertrophy, fibrosis, and capillary density loss after TAC. Following TAC, in vivo left ventricular developed pressure was decreased in G1KO hearts relative to controls, but+dP/dt was equivalently reduced in Cont and G1KO mice. Mitochondrial function was equivalently impaired following TAC in both Cont and G1KO hearts. GLUT1 deficiency in cardiomyocytes alters myocardial substrate utilization, but does not substantially exacerbate pressure-overload induced contractile dysfunction or accelerate the progression to heart failure.

The absence of insulin signaling in the heart induces changes in potassium channel expression and ventricular repolarization

Diabetes mellitus increases the risk for cardiac dysfunction, heart failure, and sudden death. The wide array of neurohumoral changes associated with diabetes pose a challenge to understanding the roles of specific pathways that alter cardiac function. Here, we use a mouse model with cardiomyocyte-restricted deletion of insulin receptors (CIRKO, cardiac-specific insulin receptor knockout) to study the specific effects of impaired cardiac insulin signaling on ventricular repolarization, independent of the generalized metabolic derangements associated with diabetes. Impaired insulin action caused a reduction in mRNA and protein expression of several key K(+) channels that dominate ventricular repolarization. Specifically, components of transient outward K(+) current fast component (Ito,fast; Kv4.2 and KChiP2) were reduced, consistent with a reduction in the amplitude of Ito,fast in isolated left ventricular CIRKO myocytes, compared with littermate controls. The reduction in Ito,fast resulted in ventricular action potential prolongation and prolongation of the QT interval on the surface ECG. These results support the notion that the lack of insulin signaling in the heart is sufficient to cause the repolarization abnormalities described in other animal models of diabetes.

Inducible overexpression of GLUT1 prevents mitochondrial dysfunction and attenuates structural remodeling in pressure overload but does not prevent left ventricular dysfunction

BACKGROUND

Increased glucose transporter 1 (GLUT1) expression and glucose utilization that accompany pressure overload-induced hypertrophy (POH) are believed to be cardioprotective. Moreover, it has been shown that lifelong transgenic overexpression of GLUT1 in the heart prevents cardiac dysfunction after aortic constriction. The relevance of this model to clinical practice is unclear because of the life-long duration of increased glucose metabolism. Therefore, we sought to determine if a short-term increase in GLUT1-mediated myocardial glucose uptake would still confer cardioprotection if overexpression occurred at the onset of POH.

METHODS AND RESULTS

Mice with cardiomyocyte-specific inducible overexpression of a hemagglutinin (HA)-tagged GLUT1 transgene (G1HA) and their controls (Cont) were subjected to transverse aortic constriction (TAC) 2 days after transgene induction with doxycycline (DOX). Analysis was performed 4 weeks after TAC. Mitochondrial function, adenosine triphosphate (ATP) synthesis, and mRNA expression of oxidative phosphorylation (OXPHOS) genes were reduced in Cont mice, but were maintained in concert with increased glucose utilization in G1HA following TAC. Despite attenuated adverse remodeling in G1HA relative to control TAC mice, cardiac hypertrophy was exacerbated in these mice, and positive dP/dt (in vivo) and cardiac power (ex vivo) were equivalently decreased in Cont and G1HA TAC mice compared to shams, consistent with left ventricular dysfunction. O-GlcNAcylation of Ca2+ cycling proteins was increased in G1HA TAC hearts.

CONCLUSIONS

Short-term cardiac specific induction of GLUT1 at the onset of POH preserves mitochondrial function and attenuates pathological remodeling, but exacerbates the hypertrophic phenotype and is insufficient to prevent POH-induced cardiac contractile dysfunction, possibly due to impaired calcium cycling.

Cardiac PI3K-Akt impairs insulin-stimulated glucose uptake independent of mTORC1 and GLUT4 translocation

Impaired insulin-mediated glucose uptake characterizes cardiac muscle in humans and animals with insulin resistance and diabetes, despite preserved or enhanced phosphatidylinositol 3-kinase (PI3K) and the serine-threonine kinase, Akt-signaling, via mechanisms that are incompletely understood. One potential mechanism is PI3K- and Akt-mediated activation of mechanistic target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6K), which may impair insulin-mediated activation of insulin receptor substrate (IRS)1/2 via inhibitory serine phosphorylation or proteasomal degradation. To gain mechanistic insights by which constitutive activation of PI3K or Akt may desensitize insulin-mediated glucose uptake in cardiomyocytes, we examined mice with cardiomyocyte-restricted, constitutive or inducible overexpression of a constitutively activated PI3K or a myristoylated Akt1 (myrAkt1) transgene that also expressed a myc-epitope-tagged glucose transporter type 4 protein (GLUT4). Although short-term activation of PI3K and myrAkt1 increased mTOR and S6 signaling, there was no impairment in insulin-mediated activation of IRS1/2. However, insulin-mediated glucose uptake was reduced by 50-80%. Although longer-term activation of Akt reduced IRS2 protein content via an mTORC1-mediated mechanism, treatment of transgenic mice with rapamycin failed to restore insulin-mediated glucose uptake, despite restoring IRS2. Transgenic activation of Akt and insulin-stimulation of myrAkt1 transgenic cardiomyocytes increased sarcolemmal insertion of myc-GLUT4 to levels equivalent to that observed in insulin-stimulated wild-type controls. Despite preserved GLUT4 translocation, glucose uptake was not elevated by the presence of constitutive activation of PI3K and Akt. Hexokinase II activity was preserved in myrAkt1 hearts. Thus, constitutive activation of PI3K and Akt in cardiomyocytes impairs GLUT4-mediated glucose uptake via mechanisms that impair the function of GLUT4 after its plasma-membrane insertion.

Advanced oxidation of bleached eucalypt kraft pulp mill effluent

In this study a poorly biodegradable (BOD/COD = 0.3) industrial alkaline ECF bleaching filtrate was treated using different advanced oxidation processes to evaluate their use in combined chemical-biological treatment aimed at increasing recalcitrant COD removal and improving final effluent quality. Oxidative treatments included ozonation combined with hydrogen peroxide (2, 5, 10, 20 mmol L(-1) O3/0.7, 2, 5, 10 mmol L(-1) H2O2) and photocatalysis with hydrogen peroxide (UV/2, 4 and 8 mmolL(-1) H2O2) and with TiO2 (UV/TiO2/0.7 and 4 mmol L(-1) H2O2). The O3/H2O2 process increased effluent biodegradability by up to 68% as a result of increasing BOD and decreasing COD. Increasing the O3 dose had a greater effect on biodegradability improvement and lignin and colour removal efficiencies than increasing the H2O2 dose. A combined oxidant dose of 5 mmol L(-1) O3 and 2 mmol L(-1) H2O2 resulted in 75% lignin removal, 40% colour removal and 6% carbohydrate loss without mineralizing the organic carbon. The photocatalytic processes led to a decrease in effluent biodegradability through combined decrease in BOD and increase in COD and did not result in efficient lignin or colour removal. Photocatalytic oxidation was apparently inhibited by the high chloride and COD levels in the alkaline filtrate, and may be more efficient in recalcitrant COD removal if performed after biological.

Osteopontin expression in coculture of differentiating rat fetal skeletal fibroblasts and myoblasts

Skeletal fibroblasts in vitro can acquire myofibroblast phenotypes by the development of biochemical and morphological features, mainly the expression of alpha-smooth-muscle actin (alpha-SMA). Myogenic differentiation is a central event in skeletal muscle development, and has commonly been studied in vitro in the context of skeletal muscle development and regeneration. Controlling this process is a complex set of interactions between myoblasts and the extracellular matrix. Osteopontin (OPN) is an acidic, phosphorylated matrix protein that contains an Arg-Gly-Asp (RGD) cell attachment sequence and has been identified as an adhesive and migratory substrate for several cell types. The aim of this study was to investigate osteopontin expression during the differentiation of skeletal fibroblasts into myofibroblasts and during myogenesis in a coculture model. Fibroblasts and myoblasts were obtained from skeletal muscle of 18-d-old Wistar strain rat fetuses by enzymatic dissociation. At 1 and 9 d, cocultures were immunolabeled, and the cells were also separately subjected to Western blotting to analyze OPN expression. Our data using confocal microscopy showed that myoblasts displayed a strong staining for OPN and that this labeling was maintained after myotube differentiation. Conversely, during fibroblast differentiation into myofibroblasts, we observed a significant increase in OPN expression. The results obtained by immunolabeling were confirmed by Western blotting. We suggest that OPN is important mainly during early stages of myogenesis, facilitating myoblast fusion and differentiation, and that the increased expression of OPN in myofibroblasts might be related to its effects as a key cytokine regulating tissue repair and inflammation.

Enhancement of lipid bodies during differentiation of skeletal myofibroblasts of rat's fetus in vitro

Fibroblasts in vitro can acquire myofibroblast phenotype by the development of several biochemical and morphological properties of smooth muscle cells, particularly the expression of alpha-smooth muscle actin. These cells play a major role in inflammatory responses and in wound repair through their production of growth factors, cytokines, and other soluble mediators. Lipid bodies (LB) are lipid-rich cytoplasmic inclusions and have been recognized as specialized intracellular domains involved in the formation of paracrine mediators of inflammation. The aim of the present study was to investigate the occurrence and distribution of LB during differentiation of rat fetus skeletal fibroblasts into myofibroblasts in vitro. Primary cultures of fibroblasts were obtained from skeletal muscles of 18-d-old Wistar strain rat fetus by enzymatic dissociation. At 1-7 d, the cells were stained with Nile red vital dye to identify LB and then observed under a Zeiss CLSM-310. Our results showed that there was an accentuated increase in the number of LB during the differentiation of skeletal fibroblasts into myofibroblasts and that these inclusions were scattered at the cytoplasm.