The disruption of mitochondrial axonal transport is an early event in neuroinflammation

Background: in brain inflammatory diseases, axonal damage is one of the most critical steps in the cascade that leads to permanent disability. Thus, identifying the initial events triggered by inflammation or oxidative stress that provoke axonal damage is critical for the development of neuroprotective therapies. Energy depletion due to mitochondrial dysfunction has been postulated as an important step in the damage of axons. This prompted us to study the effects of acute inflammation and oxidative stress on the morphology, transport, and function of mitochondria in axons. Methods: mouse cerebellar slice cultures were challenged with either lipopolysaccharide (LPS) or hydrogen peroxide (H2O2) ex vivo for 24 h. Axonal mitochondrial morphology was evaluated by transmission electron microscopy (TEM) and mitochondrial transportation by time-lapse imaging. In addition, mitochondrial function in the cerebellar slice cultures was analyzed through high-resolution respirometry assays and quantification of adenosine triphosphate (ATP) production. Results: both conditions promoted an increase in the size and complexity of axonal itochondria evident in electron microscopy images, suggesting a compensatory response. Such compensation was reflected at the tissue level as increased respiratory activity of complexes I and IV and as a transient increase in ATP production in response to acute inflammation. Notably, time-lapse microscopy indicated that mitochondrial transport (mean velocity) was severely impaired in axons, increasing the proportion of stationary mitochondria in axons after LPS challenge. Indeed, the two challenges used produced different effects: inflammation mostly reducing retrograde transport and oxidative stress slightly enhancing retrograde transportation. Conclusions: neuroinflammation acutely impairs axonal mitochondrial transportation, which would promote an inappropriate delivery of energy throughout axons and, by this way, contribute to axonal damage. Thus, preserving axonal mitochondrial transport might represent a promising avenue to exploit as a therapeutic target for neuroprotection in brain inflammatory diseases like multiple sclerosis

Effects of Lifestyle Intervention in Tissue-Specific Lipidomic Profile of Formerly Obese Mice

Lipids are highly diverse in their composition, properties and distribution in different biological entities. We aim to establish the lipidomes of several insulin-sensitive tissues and to test their plasticity when divergent feeding regimens and lifestyles are imposed. Here, we report a proton nuclear magnetic resonance (1H-NMR) study of lipid abundance across 4 tissues of C57Bl6J male mice that includes the changes in the lipid profile after every lifestyle intervention. Every tissue analysed presented a specific lipid profile irrespective of interventions. Glycerolipids and fatty acids were most abundant in epididymal white adipose tissue (eWAT) followed by liver, whereas sterol lipids and phosphoglycerolipids were highly enriched in hypothalamus, and gastrocnemius had the lowest content in all lipid species compared to the other tissues. Both when subjected to a high-fat diet (HFD) and after a subsequent lifestyle intervention (INT), the lipidome of hypothalamus showed no changes. Gastrocnemius and liver revealed a pattern of increase in content in many lipid species after HFD followed by a regression to basal levels after INT, while eWAT lipidome was affected mainly by the fat composition of the administered diets and not their caloric density. Thus, the present study demonstrates a unique lipidome for each tissue modulated by caloric intake and dietary composition. Keywords: lipidomics; tissue-specific; plasticity; energy intake; diet composition; exercise; hypothalamus; gastrocnemius; liver; white adipose tissu

Dietary betaine supplementation increases Fgf21 levels to improve glucose homeostasis and reduce hepatic lipid accumulation in mice

Identifying markers of human insulin resistance may permit development of new approaches for treatment and prevention of type 2 diabetes. To this end, we analyzed the fasting plasma metabolome in metabolically characterized human volunteers across a spectrum of insulin resistance. We demonstrate that plasma betaine levels are reduced in insulin-resistant humans and correlate closely with insulin sensitivity. Moreover, betaine administration to mice with diet-induced obesity prevents the development of impaired glucose homeostasis, reduces hepatic lipid accumulation, increases white adipose oxidative capacity, and enhances whole-body energy expenditure. In parallel with these beneficial metabolic effects, betaine supplementation robustly increased hepatic and circulating fibroblast growth factor (Fgf)21 levels. Betaine administration failed to improve glucose homeostasis and liver fat content in Fgf21(-/-) mice, demonstrating that Fgf21 is necessary for betaine's beneficial effects. Together, these data indicate that dietary betaine increases Fgf21 levels to improve metabolic health in mice and suggest that betaine supplementation merits further investigation as a supplement for treatment or prevention of type 2 diabetes in humans

Remission of obesity and insulin resistance is not sufficient to restore mitochondrial homeostasis in visceral adipose tissue

Metabolic plasticity is the ability of a biological system to adapt its metabolic phenotype to different environmental stressors. We used a whole-body and tissue-specific phenotypic, functional, proteomic, metabolomic and transcriptomic approach to systematically assess metabolic plasticity in diet-induced obese mice after a combined nutritional and exercise intervention. Although most obesity and overnutrition-related pathological features were successfully reverted, we observed a high degree of metabolic dysfunction in visceral white adipose tissue, characterized by abnormal mitochondrial morphology and functionality. Despite two sequential therapeutic interventions and an apparent global healthy phenotype, obesity triggered a cascade of events in visceral adipose tissue progressing from mitochondrial metabolic and proteostatic alterations to widespread cellular stress, which compromises its biosynthetic and recycling capacity. In humans, weight loss after bariatric surgery showed a transcriptional signature in visceral adipose tissue similar to our mouse model of obesity reversion. Overall, our data indicate that obesity prompts a lasting metabolic fingerprint that leads to a progressive breakdown of metabolic plasticity in visceral adipose tissue

Assessing metabolic plasticity in diet-induced obese mice upon lifestyle intervention. An integrative approach

[eng] Type 2 Diabetes Mellitus (T2DM) is the metabolic disorder that accounts for the presence of hyperglycemia within insulin resistance (IR). The International Diabetes Federation estimated in 2013 that 382 million people (8.3% of world society ) had diabetes and that this number is set to rise beyond 592 million people in the next 22 years. T2DM accounts for 90% of people with diabetes (WHO 1999). Obesity is considered a major risk factor for developing T2DM over time. The World Health Organization (WHO) stated in 2014 that more than 1.9 billion adults were overweight and of these, over 600 million were obese (body mass index (BMI) > 30 kg/m2). Besides healthcare costs, WHO projects that diabetes will be the 7th leading cause of death in 2030 (Mathers & Loncar 2006). Once T2DM is diagnosed, the first therapeutic approach is by lifestyle counselling consisting of an increase in physical activity and changes in the patient dietary habits. The aim of this project is to study and integrate the metabolic responses that regulate systemic glucose homeostasis. We are not aware of other works describing in a holistic way the different metabolic processes regulating glucose homeostasis in different tissues that play an important role during the development and onset of diet-induced T2DM. With this approach, we will gain more insight and a better knowledge of the metabolic alterations taking place during an obese state induced by high-fat diet, as well as assess the degree of reversibility that can be reached by undergoing a lifestyle intervention, known as “metabolic plasticity”. For this purpose a diet-induced obese animal model of T2DM is used. To achieve the presented aims, a phenotypical and funcional study is performed at systemic level in order to complete a more experimental and detailed approach afterwards in each of the studied tissues: pancreas, white adipose tissue, liver, oxidative and glycolytic skeletal muscle, and hypothalamus. This experimental approach encompasses tissue-specific-functional analysis, gene expression studies, protein content determination and signalling, metabolomics and RNAseq. Likewise, systems biology tools have been developed and have allowed to measure several correlations as well as perform different types of multivariant analysis with the studied parameters. Three experimental groups are defined representing the metabolic stages of interest: control group (Ctrl); pathologic group (HFD, that mimic diet-induced T2DM after 16 wks on HFD; and in which animals showed overweight, and fasting hyperglycemia and hyperinsulinemia); and a third group (Int) that follows a lifestyle intervention consisting of caloric restriction, modification of the fatty acid source and carbohydrates in the diet, and the performance of an exercise training programme. The diet-induced obese experimental group (HFD group) reported the typical physiological features of the pathological state: overweight, fasting hyperglycemia, hyperinsulinemia and hyperleptinemia, increase in fat mass and volume, increase of white adipose tissue, liver and pancreas weight, increase of liver and oxidative skeletal muscle triglycerice levels, glucose intolerance, insulin resistance, increase in beta-cell mass along with hypertrophic enlarged islets and dysfunction in glucose-stimulated insulin secretion in vivo and in vitro, and a diminishment in oxygen consumption, heat production and scapular temperature. Lifestyle intervention was enough to revert most of the disruptions reported in the pathological group. However, certain irreversibility degree was still observed in particular studied parameters: (1) alteration in fasting glucose and glucose-stimulated insulin secretion in vivo, (2) increment in pancreatic beta-cell area, (3) affectation in the epididymal white adipose tissue with inflammation and immune cell infiltration, as well as (4) mitochondria dysfunction, already observed in the pathological state. Taken all this together, we can conclude that the pathological state left a certain degree of metabolic irreversibility does not allow a total recovery of the phenotype across the different tissues studied, at least with this type of intervention and timings. The development and application of systems biology tools have allowed the study the irreversibility degree in an integrative mode, the correlations among certain parameters at a multiorganic level, the gene expression patterns of complexes described from a protein-protein interaction (PPI) network. These strategies and computational approaches have led to the identification of most of the altered tissues and metabòlic pathways in the different states under study.[cat] La Diabetes Mellitus del tipus 2 (DM2) és una malaltia que es caracteritza per uns nivells elevats de glucosa i insulina circulants ocasionats per un estat de resistència a la insulina. Segons la International Diabetes Federation, el 2013 382 milions de persones van ser diagnosticades de diabetes (8.3% de la població mundial), i d’acord amb les prediccions aquesta xifra augmentarà fins els 592 milions en els pròxims 22 anys. La DM2 explica el 90% dels casos de diabetes (WHO 1999). L’obesitat és un factor de risc per la DM2 i avui en dia suposa una epidèmia: el 2014 la OMS va xifrar en 1.9 bilions la població adulta amb sobrepès i 600 milions amb obesitat. A part del cost econòmic que suposa per a la societat, la OMS va projectar que el 2013 la DM2 serà la setena causa de mort al món (Mathers & Loncar 2006). Un cop diagnosticada, la primera aproximació en l’assessorament al pacient amb DM2 o en un estat de risc consisteix en una intervenció en l’estil de vida: incrementant l’activitat física i portant a terme una dieta equilibrada i saludable. Aquest projecte té com a objectiu l’estudi i la integració de les respostes metabòliques responsables de regular l’homeostasi de la glucosa a nivell sistèmic. Avui en dia, no existeix cap treball que descrigui de forma holística els diferents processos metabòlics que regulen l’homeostasi de la glucosa en tots els teixits que juguen un paper determinant durant el desenvolupament de la DM2 associada a l’obesitat. D’aquesta manera, es pretén guanyar coneixement sobre les alteracions metabòliques que tenen lloc en un estat d’obesitat induït per una dieta rica en greixos, i així mateix valorar el grau de reversibilitat que es pot assolir mitjançant una intervenció en l’estil de vida, al que ens referim com a “plasticitat metabòlica”. Utilitzem un model animal d’obesitat i DM2 induïda per una dieta alta en greixos. Per aconseguir els objectius plantejats inicialment es realitza un estudi fenotípic i funcional a nivell sistèmic per més tard realizar una aproximació experimental més exhaustiva en cadascun dels teixits d’interès: pàncrees, teixit adipós blanc, fetge, múscul esquelètic oxidatiu i glicolític, i hipotàlem. Aquesta aproximació experimental engloba anàlisis funcionals-teixit específic, estudis d’expressió gènica, determinació del contingut proteic i les vies de senyalització, metabolòmica i RNAseq. Així mateix, s’han desenvolupat eines de biologia de sistemes que han permès calcular diferents correlacions i fer diferents tipus d’anàlisis multivariant amb tots els paràmetres estudiats. Es defineixen tres grups experimentals d’animals que concreten els estats metabòlics d’interès: grup control (Ctrl); grup patològic (HFD) (que simula la DM2 induïda per la dieta grassa durant 16 setmanes, i en què els animals tenen sobreprès i la glucosa i insulina circulants elevades en dejú); i un tercer grup que segueix una intervenció en l’estil de vida (Int) que consisteix en restricció calòrica, una modificació de la font d’àcids grassos i hidrats de carboni de la dieta, juntament amb la realització d’un programa d’exercici. El grup experimental d’obesitat induïda per una dieta grassa (grup HFD) presenta les característiques fisiològiques pròpies de l’estat patològic: sobrepès, hiperglucèmia, hiperinsulinèmia i hiperleptinèmia en dejú, augment de la massa i el volum de greix, augment del pes del teixit adipós blanc, el fetge i el pàncrees, augment dels nivells de triglicèrids en fetge i múscul oxidatiu, intolerància a la glucosa, resistència a la insulina, augment de la massa de cèl·lula beta en el pàncrees juntament amb illots hipertròfics engrandits i disfunció de la secreció d’insulina estimulada per glucosa in vivo i in vitro, i disfunció del consum d’oxigen, generació de calor i temperatura escapular. La intervenció va ser suficient per revertir gran part de les alteracions observades en el grup patològic. No obstant, encara s’observa cert grau d’irreversibilitat en determinats paràmetres estudiats: (1) alteració de la glucosa en dejú i la resposta insulínica davant d’un estímul de glucosa in vivo, (2) increment en l’àrea de cèl·lula beta pancreàtica, (3) afectació en el teixit adipós blanc epididimal amb la presència d’inflamació i infiltració de cèl·lules immunes, així com (4) disfunció mitocondrial, ja observats en l’estat patològic. Amb tot, podem concloure que l’estat patològic deixa un cert grau d’irreversibilitat metabòlica no permetent així una recuperació total del fenotip en tots els teixits estudiats, almenys, amb aquest tipus d’intervenció i aquests períodes de temps. El desenvolupament i l’aplicació d’eines de biologia de sistemes han permès estudiar el grau de reversibilitat d’una manera integrada, les correlacions entre paràmetres concrets a nivel multiorgànic, el patró d’expressió gènica de complexes descrits en una xarxa de protein-protein-interaction (PPI). Aquestes estratègies computacionals han permès identificar aquells teixits i vies metabòliques més alterades en els diferents estats estudiats

The disruption of mitochondrial axonal transport is an early event in neuroinflammation

Background: in brain inflammatory diseases, axonal damage is one of the most critical steps in the cascade that leads to permanent disability. Thus, identifying the initial events triggered by inflammation or oxidative stress that provoke axonal damage is critical for the development of neuroprotective therapies. Energy depletion due to mitochondrial dysfunction has been postulated as an important step in the damage of axons. This prompted us to study the effects of acute inflammation and oxidative stress on the morphology, transport, and function of mitochondria in axons. Methods: mouse cerebellar slice cultures were challenged with either lipopolysaccharide (LPS) or hydrogen peroxide (H2O2) ex vivo for 24 h. Axonal mitochondrial morphology was evaluated by transmission electron microscopy (TEM) and mitochondrial transportation by time-lapse imaging. In addition, mitochondrial function in the cerebellar slice cultures was analyzed through high-resolution respirometry assays and quantification of adenosine triphosphate (ATP) production. Results: both conditions promoted an increase in the size and complexity of axonal itochondria evident in electron microscopy images, suggesting a compensatory response. Such compensation was reflected at the tissue level as increased respiratory activity of complexes I and IV and as a transient increase in ATP production in response to acute inflammation. Notably, time-lapse microscopy indicated that mitochondrial transport (mean velocity) was severely impaired in axons, increasing the proportion of stationary mitochondria in axons after LPS challenge. Indeed, the two challenges used produced different effects: inflammation mostly reducing retrograde transport and oxidative stress slightly enhancing retrograde transportation. Conclusions: neuroinflammation acutely impairs axonal mitochondrial transportation, which would promote an inappropriate delivery of energy throughout axons and, by this way, contribute to axonal damage. Thus, preserving axonal mitochondrial transport might represent a promising avenue to exploit as a therapeutic target for neuroprotection in brain inflammatory diseases like multiple sclerosis

Evaluating the potential of LiDAR data for fire damage assessment: A radiative transfer model approach

Providing accurate information on fire effects is critical to understanding post-fire ecological processes and to design appropriate land management strategies. Multispectral imagery from optical passive sensors is commonly used to estimate fire damage, yet this type of data is only sensitive to the effects in the upper canopy. This paper evaluates the sensitivity of full waveform LiDAR data to estimate the severity of wildfires using a 3D radiative transfer model approach. The approach represents the first attempt to evaluate the effect of different fire impacts, i.e. changes in vegetation structure as well as soil and leaf color, on the LiDAR signal. The FLIGHT 3D radiative transfer model was employed to simulate full waveform data for 10 plots representative of Mediterranean ecosystems along with a wide range of post-fire scenarios characterized by different severity levels, as defined by the composite burn index (CBI). A new metric is proposed, the waveform area relative change (WARC), which provides a comprehensive severity assessment considering all strata and accounting for changes in structure and leaf and soil color. It showed a strong correlation with CBI values (Spearman's Rho = 0.9 ± 0.02), outperforming the relative change of LiDAR metrics commonly applied for vegetation modeling, such as the relative height of energy quantiles (Spearman's Rho = 0.56 ± 0.07, for the relative change of RH60, the second strongest correlation). Logarithmic models fitted for each plot based on the WARC yielded very good performance with R2 (± standard deviation) and RMSE (± standard deviation) of 0.8 (± 0.05) and 0.22 (± 0.03), respectively. LiDAR metrics were evaluated over the King Fire, California, U.S., for which pre- and post-fire discrete return airborne LiDAR data were available. Pseudo-waveforms were computed after radiometric normalization of the intensity data. The WARC showed again the strongest correlation with field measures of GeoCBI values (Spearman's Rho = 0.91), closely followed by the relative change of RH40 (Spearman's Rho = 0.89). The logarithmic model fitted using WARC offered an R2 of 0.78 and a RMSE of 0.37. The accurate results obtained for the King Fire, with very different vegetation characteristics compared to our simulated data, demonstrate the robustness of the new metric proposed and its generalization capabilities to estimate the severity of fires.Peer reviewe

Dietary betaine supplementation increases Fgf21 levels to improve glucose homeostasis and reduce hepatic lipid accumulation in mice

Identifying markers of human insulin resistance may permit development of new approaches for treatment and prevention of type 2 diabetes. To this end, we analyzed the fasting plasma metabolome in metabolically characterized human volunteers across a spectrum of insulin resistance. We demonstrate that plasma betaine levels are reduced in insulin-resistant humans and correlate closely with insulin sensitivity. Moreover, betaine administration to mice with diet-induced obesity prevents the development of impaired glucose homeostasis, reduces hepatic lipid accumulation, increases white adipose oxidative capacity, and enhances whole-body energy expenditure. In parallel with these beneficial metabolic effects, betaine supplementation robustly increased hepatic and circulating fibroblast growth factor (Fgf)21 levels. Betaine administration failed to improve glucose homeostasis and liver fat content in Fgf21(-/-) mice, demonstrating that Fgf21 is necessary for betaine's beneficial effects. Together, these data indicate that dietary betaine increases Fgf21 levels to improve metabolic health in mice and suggest that betaine supplementation merits further investigation as a supplement for treatment or prevention of type 2 diabetes in humans

Dietary betaine supplementation increases Fgf21 levels to improve glucose homeostasis and reduce hepatic lipid accumulation in mice

Identifying markers of human insulin resistance may permit development of new approaches for treatment and prevention of type 2 diabetes. To this end, we analyzed the fasting plasma metabolome in metabolically characterized human volunteers across a spectrum of insulin resistance. We demonstrate that plasma betaine levels are reduced in insulin-resistant humans and correlate closely with insulin sensitivity. Moreover, betaine administration to mice with diet-induced obesity prevents the development of impaired glucose homeostasis, reduces hepatic lipid accumulation, increases white adipose oxidative capacity, and enhances whole-body energy expenditure. In parallel with these beneficial metabolic effects, betaine supplementation robustly increased hepatic and circulating fibroblast growth factor (Fgf)21 levels. Betaine administration failed to improve glucose homeostasis and liver fat content in Fgf21(-/-) mice, demonstrating that Fgf21 is necessary for betaine's beneficial effects. Together, these data indicate that dietary betaine increases Fgf21 levels to improve metabolic health in mice and suggest that betaine supplementation merits further investigation as a supplement for treatment or prevention of type 2 diabetes in humans