Autophagy ablation in skeletal muscles worsens sepsis-induced muscle wasting, impairs whole-body metabolism, and decreases survival.

Septic patients frequently develop skeletal muscle wasting and weakness, resulting in severe clinical consequences and adverse outcomes. Sepsis triggers sustained induction of autophagy, a key cellular degradative pathway, in skeletal muscles. However, the impact of enhanced autophagy on sepsis-induced muscle dysfunction remains unclear. Using an inducible and muscle-specific Atg7 knockout mouse model (Atg7iSkM-KO), we investigated the functional importance of skeletal muscle autophagy in sepsis using the cecal ligation and puncture model. Atg7iSkM-KO mice exhibited a more severe phenotype in response to sepsis, marked by severe muscle wasting, hypoglycemia, higher ketone levels, and a decreased in survival as compared to mice with intact Atg7. Sepsis and Atg7 deletion resulted in the accumulation of mitochondrial dysfunction, although sepsis did not further worsen mitochondrial dysfunction in Atg7iSkM-KO mice. Overall, our study demonstrates that autophagy inactivation in skeletal muscles triggers significant worsening of sepsis-induced muscle and metabolic dysfunctions and negatively impacts survival.

The impact of high-fat feeding and parkin overexpression on skeletal muscle mass, mitochondrial respiration, and H2O2 emission.

Obesity is a major risk factor for developing various health problems, including insulin resistance and type 2 diabetes. Although controversial, accumulation of mitochondrial dysfunction, and notably an increase in mitochondrial reactive oxygen species (ROS) production, was proposed as a key contributor leading to obesity-induced insulin resistance. Here, our goal was to investigate whether Parkin overexpression, a key regulator of the removal of dysfunctional mitochondria through mitophagy, could confer protection against obesity-induced mitochondrial dysfunction. To this end, intramuscular injections of adeno-associated viruses (AAVs) were performed to overexpress Parkin in limb muscle of 6-mo-old mice fed a control diet (CD) or a high-fat diet (HFD) for 12 wk. An AAV-expressing the green fluorescent protein (GFP) was used as control. HFD increased fat mass, altered glycemia, and resulted in insulin resistance. Parkin overexpression resulted in an increase in muscle mass in both CD and HFD mice. In CD mice, Parkin overexpression increased maximal mitochondrial respiration and lowered H2O2 emission. HFD increased mitochondrial respiration and, surprisingly, also lowered H2O2 emission. Parkin overexpression did not significantly impact mitochondrial function in HFD mice. Taken altogether, our results indicate that Parkin overexpression positively impacts muscle and mitochondrial health under basal conditions and challenges the notion that intrinsic mitochondrial dysfunction is involved in the development of insulin resistance caused by high-fat feeding.

Clinical and Biological Adaptations in Obese Older Adults Following 12-Weeks of High-Intensity Interval Training or Moderate-Intensity Continuous Training.

Sarcopenia and obesity are considered a double health burden. Therefore, the implementation of effective strategies is needed to improve the quality of life of older obese individuals. The aim of this study was to compare the impact of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on functional capacities, muscle function, body composition and blood biomarkers in obese older adults. Adipose tissue gene expression and markers of muscle mitochondrial content and quality control involved in exercise adaptations were also investigated. Sixty-eight participants performed either HIIT (n = 34) on an elliptical trainer or MICT (n = 34) on a treadmill, three times per week for 12 weeks. HIIT produced significantly higher benefits on some physical parameters (six-minute walking test (HIIT: +12.4% vs. MICT: +5.2%); step test (HIIT: +17.02% vs. MICT: +5.9%); ten-repetition chair test (HIIT: -17.04% vs. MICT: -4.7%)). Although both HIIT and MICT led to an improvement in lower limb power (HIIT: +25.2% vs. MICT: +20.4%), only MICT led to higher improvement in lower limb muscle strength (HIIT: +4.3% vs. MICT: +23.2%). HIIT was more beneficial for increasing total lean body mass (HIIT: +1.58% vs. MICT: -0.81%), while MICT was more effective for decreasing relative gynoid fat mass (HIIT: -1.09% vs. MICT: -4.20%). Regarding adipose tissue gene expression, a significant change was observed for cell death-inducing DFFA (DNA fragmentation factor-alpha)-like effector A (CIDEA) in the HIIT group (A.U; HIIT at T0: 32.10 ± 39.37 vs. HIIT at T12: 48.2 ± 59.2). Mitochondrial transcription factor A (TFAM) content, a marker of mitochondrial biogenesis, increased significantly following HIIT (+36.2%) and MICT (+57.2%). A significant increase was observed in the HIIT group for Translocase of Outer Membrane 20 (TOM20; +54.1%; marker of mitochondrial content), Mitofusin-2 (MFN2; +71.6%; marker of mitochondrial fusion) and Parkin RBR E3 Ubiquitin Protein Ligase (PARKIN; +42.3%; marker of mitophagy). Overall, our results indicate that even though MICT (walking on treadmill) and HIIT (on an elliptical) are effective intervention strategies in obese older adults, HIIT appears to have slightly more beneficial effects. More specifically, HIIT led to higher improvements than MICT on functional capacities, lean mass and skeletal muscle markers of mitochondrial content, fusion, and mitophagy. Thus, MICT but also HIIT (time-efficient training) could be recommended as exercise modalities for obese older adults to maintain or improve mobility, health and quality of life.

Impact of high-intensity interval training with or without l-citrulline on physical performance, skeletal muscle, and adipose tissue in obese older adults.

BACKGROUND: Aging is associated with a progressive decline in skeletal muscle mass and strength as well as an increase in adiposity. These changes may have devastating impact on the quality of life of older adults. Mitochondrial dysfunctions have been implicated in aging-related and obesity-related deterioration of muscle function. Impairments in mitochondrial quality control processes (biogenesis, fusion, fission, and mitophagy) may underlie this accumulation of mitochondrial dysfunction. High-intensity interval training (HIIT) was shown to improve muscle and mitochondrial function in healthy young and old adults and to improve body composition in obese older adults. Recent studies also positioned citrulline (CIT) supplementation as a promising intervention to counter obesity-related and aging-related muscle dysfunction. In the present study, our objectives were to assess whether HIIT, alone or with CIT, improves muscle function, functional capacities, adipose tissue gene expression, and mitochondrial quality control processes in obese older adults. METHODS: Eighty-one-old and obese participants underwent a 12 week HIIT with or without CIT on an elliptical trainer [HIIT-CIT: 20 men/25 women, 67.2 ± 5.0 years; HIIT-placebo (PLA): 18 men/18 women, 68.1 ± 4.1 years]. Handgrip and quadriceps strength, lower limb muscle power, body composition, waist circumference, and functional capacities were assessed pre and post intervention. Vastus lateralis muscle biopsies were performed in a subset of participants to quantify markers of mitochondrial content (TOM20 and OXPHOS subunits), biogenesis (TFAM), fusion (MFN1&2, OPA1), fission (DRP1), and mitophagy (Parkin). Subcutaneous abdominal adipose tissue biopsies were also performed to assess the expression of genes involved in lipid metabolism. RESULTS: HIIT-PLA and HIIT-CIT displayed improvements in functional capacities (P < 0.05), total (mean ± SD: HIIT-PLA: +1.27 ± 3.19%, HIIT-CIT: +1.05 ± 2.91%, P < 0.05) and leg lean mass (HIIT-PLA: +1.62 ± 3.85%, HIIT-CIT: +1.28 ± 4.82%, P < 0.05), waist circumference (HIIT-PLA: -2.2 ± 2.9 cm, HIIT-CIT: -2.6 ± 2.5 cm, P < 0.05), and muscle power (HIIT-PLA: +15.81 ± 18.02%, HIIT-CIT: +14.62 ± 20.02%, P < 0.05). Only HIIT-CIT decreased fat mass (-1.04 ± 2.42%, P < 0.05) and increased handgrip and quadriceps strength (+4.28 ± 9.36% and +10.32 ± 14.38%, respectively, P < 0.05). Both groups increased markers of muscle mitochondrial content, mitochondrial fusion, and mitophagy (P < 0.05). Only HIIT-CIT decreased the expression of the lipid droplet-associated protein CIDEA (P < 0.001). CONCLUSIONS: High-intensity interval training is effective in improving functional capacities, lean mass, muscle power, and waist circumference in obese older adults. HIIT also increases markers of mitochondrial biogenesis, mitochondrial fusion, and mitophagy. Importantly, adding CIT to HIIT results in a greater increase in muscle strength and a significant decrease in fat mass. The present study therefore positions HIIT combined with CIT as an effective intervention to improve the health status of obese older adults.

Regulation of muscle and mitochondrial health by the mitochondrial fission protein Drp1 in aged mice.

KEY POINTS: The maintenance of mitochondrial integrity is critical for skeletal muscle health. Mitochondrial dynamics play key roles in mitochondrial quality control; however, the exact role that mitochondrial fission plays in the muscle ageing process remains unclear. Here we report that both Drp1 knockdown and Drp1 overexpression late in life in mice is detrimental to skeletal muscle function and mitochondrial health. Drp1 knockdown in 18-month-old mice resulted in severe skeletal muscle atrophy, mitochondrial dysfunction, muscle degeneration/regeneration, oxidative stress and impaired autophagy. Overexpressing Drp1 in 18-month-old mice resulted in mild skeletal muscle atrophy and decreased mitochondrial quality. Our data indicate that silencing or overexpressing Drp1 late in life is detrimental to skeletal muscle integrity. We conclude that modulating Drp1 expression is unlikely to be a viable approach to counter the muscle ageing process. ABSTRACT: Sarcopenia, the ageing-related loss of skeletal muscle mass and function, is a debilitating process negatively impacting the quality of life of afflicted individuals. Although the mechanisms underlying sarcopenia are still only partly understood, impairments in mitochondrial dynamics, and specifically mitochondrial fission, have been proposed as an underlying mechanism. Importantly, conflicting data exist in the field and both excessive and insufficient mitochondrial fission were proposed to contribute to sarcopenia. In Drosophila melanogaster, enhancing mitochondrial fission in midlife through overexpression of dynamin-1-like protein (Drp1) extended lifespan and attenuated several key hallmarks of muscle ageing. Whether a similar outcome of Drp1 overexpression is observed in mammalian muscles remains unknown. In this study, we investigated the impact of knocking down and overexpressing Drp1 protein for 4 months in skeletal muscles of late middle-aged (18 months) mice using intra-muscular injections of adeno-associated viruses expressing shRNA targeting Drp1 or full Drp1 cDNA. We report that knocking down Drp1 expression late in life triggers severe muscle atrophy, mitochondrial dysfunctions, degeneration/regeneration, oxidative stress and impaired autophagy. Drp1 overexpression late in life triggered mild muscle atrophy and decreased mitochondrial quality. Taken altogether, our results indicate that both overexpression and silencing of Drp1 in late middle-aged mice negatively impact skeletal muscle mass and mitochondrial health. These data suggest that Drp1 content must remain within a narrow physiological range to preserve muscle and mitochondrial integrity during ageing. Altering Drp1 expression is therefore unlikely to be a viable target to counter sarcopenia.

Parkin Overexpression Attenuates Sepsis-Induced Muscle Wasting.

Sepsis elicits skeletal muscle weakness and fiber atrophy. The accumulation of injured mitochondria and depressed mitochondrial functions are considered as important triggers of sepsis-induced muscle atrophy. It is unclear whether mitochondrial dysfunctions in septic muscles are due to the inadequate activation of quality control processes. We hypothesized that overexpressing Parkin, a protein responsible for the recycling of dysfunctional mitochondria by the autophagy pathway (mitophagy), would confer protection against sepsis-induced muscle atrophy by improving mitochondrial quality and content. Parkin was overexpressed for four weeks in the limb muscles of four-week old mice using intramuscular injections of adeno-associated viruses (AAVs). The cecal ligation and perforation (CLP) procedure was used to induce sepsis. Sham operated animals were used as controls. All animals were studied for 48 h post CLP. Sepsis resulted in major body weight loss and myofiber atrophy. Parkin overexpression prevented myofiber atrophy in CLP mice. Quantitative two-dimensional transmission electron microscopy revealed that sepsis is associated with the accumulation of enlarged and complex mitochondria, an effect which was attenuated by Parkin overexpression. Parkin overexpression also prevented a sepsis-induced decrease in the content of mitochondrial subunits of NADH dehydrogenase and cytochrome C oxidase. We conclude that Parkin overexpression prevents sepsis-induced skeletal muscle atrophy, likely by improving mitochondrial quality and contents.

Drp1 knockdown induces severe muscle atrophy and remodelling, mitochondrial dysfunction, autophagy impairment and denervation.

KEY POINTS: The maintenance of optimal mitochondrial content and function is critical for muscle health. Mitochondrial dynamics play key roles in mitochondrial quality control; however, the exact role that mitochondrial fission plays in skeletal muscle health remains unclear. Here we report knocking down Drp1 (a protein regulating mitochondrial fission) for 4 months in adult mouse skeletal muscle resulted in severe muscle atrophy (40-50%). Drp1 knockdown also led to a reduction in ADP-stimulated respiration, an increase in markers of impaired autophagy and increased muscle regeneration, denervation, fibrosis and oxidative stress. Our data indicate that Drp1 is crucial for the maintenance of normal mitochondrial function and that Drp1 depletion severely impairs muscle health. ABSTRACT: Mitochondria play central roles in skeletal muscle physiology, including energy supply, regulation of energy-sensitive signalling pathways, reactive oxygen species production/signalling, calcium homeostasis and the regulation of apoptosis. The maintenance of optimal mitochondrial content and function is therefore critical for muscle cells. Mitochondria are now well known as highly dynamic organelles, able to change their morphology through fusion and fission processes. Solid experimental evidence indicates that mitochondrial dynamics play key roles in mitochondrial quality control, and alteration in the expression of proteins regulating mitochondrial dynamics have been reported in many conditions associated with muscle atrophy and wasting. However, the exact role that mitochondrial fission plays in skeletal muscle health remains unclear. To address this issue, we investigated the impact of Drp1 (a protein regulating mitochondrial fission) knockdown, introduced via intramuscular injection of adeno-associated virus (AAV) on adult mouse skeletal muscle. Knocking down Drp1 for 4 months resulted in very severe muscle atrophy (40-50%). Drp1 knockdown also led to a reduction in ADP-stimulated respiration and increases in markers of muscle regeneration, denervation, fibrosis, oxidative stress and impaired autophagy. Our findings indicate that Drp1 is essential for the maintenance of normal mitochondrial function and that Drp1 suppression severely impairs muscle health.

Brainstem Correlates of a Cold Pressor Test Measured by Ultra-High Field fMRI.

INTRODUCTION: Modern imaging techniques such as blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) allow the non-invasive and indirect measurement of brain activity. Whether changes in signal intensity can be detected in small brainstem regions during a cold pressor test (CPT) has not been explored thoroughly. The aim of this study was to measure whole brain and brainstem BOLD signal intensity changes in response to a modified CPT. METHODS: BOLD fMRI was measured in healthy normotensive participants during a randomized crossover study (modified CPT vs. control test) using ultra-high field 7 Tesla MRI scanner. Data were analyzed using Statistical Parametric Mapping (SPM) in a whole-brain approach, and with a brainstem-specific analysis using the spatially unbiased infra-tentorial template (SUIT) toolbox. Blood pressure (BP) and hormonal responses (norepinephrine and epinephrine levels) were also measured. Paired t-test statistics were used to compare conditions. RESULTS: Eleven participants (six women, mean age 28 ± 8.9 years) were analyzed. Mean arterial BP increased from 83 ± 12 mm Hg to 87 ± 12 mm Hg (p = 0.0009) during the CPT. Whole-brain analysis revealed significant activations linked to the CPT in the right supplementary motor cortex, midcingulate (bilateral) and the right anterior insular cortex. The brainstem-specific analysis showed significant activations in the dorsal medulla. CONCLUSION: Changes in BOLD fMRI signal intensity in brainstem regions during a CPT can be detected, and show an increased response during a cold stress in healthy volunteers. Consequently, BOLD fMRI at 7T is a promising tool to explore and acquire new insights in the comprehension of neurogenic hypertension.

Processing pathways for emotional vocalizations.

Emotional sounds are processed within a large cortico-subcortical network, of which the auditory cortex, the voice area, and the amygdala are the core regions. Using 7T fMRI, we have compared the effect of emotional valence (positive, neutral, and negative) and the effect of the type of environmental sounds (human vocalizations and non-vocalizations) on neural activity within individual early stage auditory areas, the voice area, and the amygdala. A two-way ANOVA was applied to the BOLD time course within each ROI. In several early stage auditory areas, it yielded a significant main effect of vocalizations and of valence, but not a significant interaction. Significant interaction as well as significant main effects of vocalization and of valence were present in the voice area; the former was driven by a significant emotional modulation of vocalizations but not of other sounds. Within the amygdala, only the main effect of valence was significant. Post-hoc correlation analysis highlighted coupling between the voice area and early stage auditory areas during the presentation of any vocalizations, and between the voice area and the right amygdala during positive vocalizations. Thus, the voice area is selectively devoted to the encoding of the emotional valence of vocalizations; it shares with several early stage auditory areas encoding characteristics for vocalizations and with the amygdala for the emotional modulation of vocalizations. These results are indicative of a dual pathway, whereby the emotional modulation of vocalizations within the voice area integrates the input from the lateral early stage auditory areas and from the amygdala.

Multi-slice passband bSSFP for human and rodent fMRI at ultra-high field.

Balanced steady-state free precession (bSSFP) can be used as an alternative to gradient-echo (GE) EPI for BOLD functional MRI when image distortions and signal drop-outs are severe such as at ultra-high field. However, 3D-bSSFP acquisitions have distinct drawbacks on either human or animal MR systems. On clinical scanners, 3D imaging is suboptimal for localized fMRI applications. It can also display distortions when acceleration methods such as spiral read-outs are used, and, compared to multi-slice acquisitions, suffers from increased sensitivity to motion or physiological noise which further results in blurring. On pre-clinical systems, 3D acquisitions have low temporal resolution due to limited acceleration options, while single slice often results in insufficient coverage. The aim of the present study was to implement a multi-slice bSSFP acquisition with Cartesian read-out to obtain non-distorted BOLD fMRI activation maps in the human and rat brain at ultra-high field. We show that, when using a new pseudo-steady-state, the bSSFP signal characteristics are preserved. In the human brain at 7 T, we demonstrate that both task- and resting-state fMRI can be performed with multi-slice bSSFP, with a temporal SNR that matches that of 3D-bSSFP, resulting in - at least - equal performance. In the rat brain at 14 T, we show that the multi-slice bSSFP protocol has similar sensitivity to gradient-echo EPI for task fMRI, while benefitting from much reduced distortions and drop-outs. The advantages of passband bSSFP at 14 T in comparison with GE-EPI are expected to be even more marked for mouse brain.

Effects of Aging and Caloric Restriction on Fiber Type Composition, Mitochondrial Morphology and Dynamics in Rat Oxidative and Glycolytic Muscles.

Aging is associated with a progressive decline in muscle mass and strength, a process known as sarcopenia. Evidence indicates that mitochondrial dysfunction plays a causal role in sarcopenia and suggests that alterations in mitochondrial dynamics/morphology may represent an underlying mechanism. Caloric restriction (CR) is among the most efficient nonpharmacological interventions to attenuate sarcopenia in rodents and is thought to exert its beneficial effects by improving mitochondrial function. However, CR effects on mitochondrial morphology and dynamics, especially in aging muscle, remain unknown. To address this issue, we investigated mitochondrial morphology and dynamics in the oxidative soleus (SOL) and glycolytic white gastrocnemius (WG) muscles of adult (9-month-old) ad libitum-fed (AL; A-AL), old (22-month-old) AL-fed (O-AL), and old CR (O-CR) rats. We show that CR attenuates the aging-related decline in the muscle-to-body-weight ratio, a sarcopenic index. CR also prevented the effects of aging on muscle fiber type composition in both muscles. With aging, the SOL displayed fragmented SubSarcolemmal (SS) and InterMyoFibrillar (IMF) mitochondria, an effect attenuated by CR. Aged WG displayed enlarged SS and more complex/branched IMF mitochondria. CR had marginal anti-aging effects on WG mitochondrial morphology. In the SOL, DRP1 (pro-fission protein) content was higher in O-AL vs YA-AL, and Mfn2 (pro-fusion) content was higher in O-CR vs A-AL. In the gastrocnemius, Mfn2, Drp1, and Fis1 (pro-fission) contents were higher in O-AL vs A-AL. CR reduced this aging-related increase in Mfn2 and Fis1 content. Overall, these results reveal for the first time that aging differentially impacts mitochondrial morphology and dynamics in different muscle fiber types, by increasing fission/fragmentation in oxidative fibers while enhancing mitochondrial size and branching in glycolytic fibers. Our results also indicate that although CR partially attenuates aging-related changes in mitochondrial dynamics in glycolytic fibers, its anti-aging effect on mitochondrial morphology is restricted to oxidative fibers.

Parkin overexpression protects from ageing-related loss of muscle mass and strength.

KEY POINTS: Recent evidence suggests that impaired mitophagy, a process in charge of removing damaged/dysfunctional mitochondria and in part regulated by Parkin, could contribute to the ageing-related loss of muscle mass and function. In the present study, we show that Parkin overexpression attenuates ageing-related loss of muscle mass and strength and unexpectedly causes hypertrophy in adult skeletal muscles. We also show that Parkin overexpression leads to increases in mitochondrial content and enzymatic activities. Finally, our results show that Parkin overexpression protects from ageing-related increases in markers of oxidative stress, fibrosis and apoptosis. Our findings place Parkin as a potential therapeutic target to attenuate sarcopenia and improve skeletal muscle health and performance. ABSTRACT: The ageing-related loss of muscle mass and strength, a process called sarcopenia, is one of the most deleterious hallmarks of ageing. Solid experimental evidence indicates that mitochondrial dysfunctions accumulate with ageing and are critical in the sarcopenic process. Recent findings suggest that mitophagy, the process in charge of the removal of damaged/dysfunctional mitochondria, is altered in aged muscle. Impaired mitophagy represents an attractive mechanism that could contribute to the accumulation of mitochondrial dysfunctions and sarcopenia. To test this hypothesis, we investigated the impact of Parkin overexpression in skeletal muscles of young and old mice. Parkin was overexpressed for 4 months in muscles of young (3 months) and late middle-aged (18 months) mice using i.m. injections of adeno-associated viruses. We show that Parkin overexpression increased muscle mass, fibre size and mitochondrial enzyme activities in both young and old muscles. In old mice, Parkin overexpression increased muscle strength, peroxisome proliferator­activated receptor gamma coactivator 1­alpha (PGC­1α) and mitochondrial density. Parkin overexpression also attenuated the ageing-related increase in 4-hydroxynonenal content (a marker of oxidative stress) and type I collagen content (a marker of fibrosis), as well as the number of terminal deoxynucleotidyl transferase dUTP nick-end labelling-positive myonuclei (a marker of apoptosis). Overall, our results indicate that Parkin overexpression attenuates sarcopenia and unexpectedly causes hypertrophy in adult muscles. They also show that Parkin overexpression leads to increases in mitochondrial content and enzymatic activities. Finally, our results show that Parkin overexpression protects against oxidative stress, fibrosis and apoptosis. These findings highlight that Parkin may be an attractive therapeutic target with respect to attenuating sarcopenia and improving skeletal muscle health and performance.

Quantifying myofiber integrity using diffusion MRI and random permeable barrier modeling in skeletal muscle growth and Duchenne muscular dystrophy model in mice.

PURPOSE: To measure the microstructural changes during skeletal muscle growth and progressive pathologies using the random permeable model with diffusion MRI, and compare findings to conventional imaging modalities such as three-point Dixon and T2 imaging. METHODS: In vivo and ex vivo DTI experiments with multiple diffusion times (20-700 ms) were completed on wild-type (n = 22) and muscle-dystrophic mdx mice (n = 8) at various developmental time points. The DTI data were analyzed with the random permeable model framework that provides estimates of the unrestricted diffusion coefficient (D0 ), membrane surface-to-volume ratio (S/V), and membrane permeability (κ). In addition, the MRI experiments included conventional measures, such as tissue fat fractions and T2 relaxation. RESULTS: During normal muscle growth between week 4 and week 13, the in vivo S/V, fractional anisotropy, and fat fraction correlated positively with age (ρ = 0.638, 0.664, and 0.686, respectively), whereas T2 correlated negatively (ρ = -0.847). In mdx mice, all DTI random permeable model parameters and fat fraction had significant positive correlation with age, whereas fractional anisotropy and T2 did not have significant correlation with age. Histological measurements of the perimeter-to-area ratio served as a proxy for the model-derived S/V in the cylindrical myofiber geometry, and had a significant correlation with the ex vivo S/V (r = 0.71) as well as the in vivo S/V (r = 0.56). CONCLUSION: The present study demonstrates that DTI at multiple diffusion times with the random permeable model analysis allows for noninvasively quantifying muscle fiber microstructural changes during both normal muscle growth and disease progression. Future studies can apply our technique to evaluate current and potential treatments to muscle myopathies.

The impact of a short-term high-fat diet on mitochondrial respiration, reactive oxygen species production, and dynamics in oxidative and glycolytic skeletal muscles of young rats.

Multiple aspects of mitochondrial function and dynamics remain poorly studied in the skeletal muscle of pediatric models in response to a short-term high-fat diet (HFD). This study investigated the impact of a short-term HFD on mitochondrial function and dynamics in the oxidative soleus (SOL) and glycolytic extensor digitorum longus (EDL) muscles in young rats. Young male Wistar rats were submitted to either HFD or normal chow (NCD) diets for 14 days. Permeabilized myofibers from SOL and EDL were prepared to assess mitochondrial respiration and reactive oxygen species (ROS) production. The expression and content of protein involved in mitochondrial metabolism and dynamics (fusion/fission) were also quantified. While no effects of HFD was observed on mitochondrial respiration when classical complex I and II substrates were used, both SOL and EDL of rats submitted to a HFD displayed higher basal and ADP-stimulated respiration rates when Malate + Palmitoyl-L-carnitine were used as substrates. HFD did not alter ROS production and markers of mitochondrial content. The expression of CPT1b was significantly increased in SOL and EDL of HFD rats. Although the expression of UCP3 was increased in SOL and EDL muscles from HFD rats, mitochondrial coupling efficiency was not altered. In SOL of HFD rats, the transcript levels of Mfn2 and Fis1 were significantly upregulated. The expression and content of proteins regulating mitochondrial dynamics was not modulated by HFD in the EDL. Finally, DRP1 protein content was increased by over fourfold in the SOL of HFD rats. Taken altogether, our findings show that exposing young animals to short-term HFD results in an increased capacity of skeletal muscle mitochondria to oxidize fatty acids, without altering ROS production, coupling efficiency, and mitochondrial content. Our results also highlight that the impact of HFD on mitochondrial dynamics appears to be muscle specific.

High spatio-temporal resolution in functional MRI with 3D echo planar imaging using cylindrical excitation and a CAIPIRINHA undersampling pattern.

PURPOSE: The combination of 3D echo planar imaging (3D-EPI) with a 2D-CAIPIRINHA undersampling scheme provides high flexibility in the optimization for spatial or temporal resolution. This flexibility can be increased further with the addition of a cylindrical excitation pulse, which exclusively excites the brain regions of interest. Here, 3D-EPI was combined with a 2D radiofrequency pulse to reduce the brain area from which signal is generated, and hence, allowing either reduction of the field of view or reduction of parallel imaging noise amplification. METHODS: 3D-EPI with cylindrical excitation and 4 × 3-fold undersampling in a 2D-CAIPIRINHA sampling scheme was used to generate functional MRI (fMRI) data with either 2-mm or 0.9-mm in-plane resolution and 1.1-s temporal resolution over a 5-cm diameter cylinder placed over both temporal lobes for an auditory fMRI experiment. RESULTS: Significant increases in image signal-to-noise ratio (SNR) and temporal SNR (tSNR) were found for both 2-mm isotropic data and the high-resolution protocol when using the cylindrical excitation pulse. Both protocols yielded highly significant blood oxygenation level-dependent responses for the presentation of natural sounds. CONCLUSION: The higher tSNR of the cylindrical excitation 3D-EPI data makes this sequence an ideal choice for high spatiotemporal resolution fMRI acquisitions. Magn Reson Med 79:2589-2596, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

[Skeletal muscle aging and mitochondrial dysfunction: an update]. / Dysfonctions mitochondriales et vieillissement musculaire - Une mise à jour.

One of the most obvious and deleterious changes occurring with aging is a progressive loss of skeletal muscle mass and strength, a physiological process named sarcopenia. Amongst the multiple theories that have been put forward to explain sarcopenia, the mitochondrial theory of aging, which postulates that the accumulation of mitochondrial dysfunctions with aging plays a causal role in muscle atrophy, has focused intense research effort and attention in the past decades. The generally accepted view of this theory is that, due to the reactive oxygen species (ROS) production inherent to respiratory chain activity, oxidative damage to mitochondrial proteins, lipids and DNA accumulates with aging. This damage is thought to (i) exacerbate mitochondrial ROS production, (ii) impair the capacity of mitochondria to adequately match the cellular ATP demand and (iii) trigger mitochondrial-mediated apoptosis. Although very appealing, this theory remains controversial. The aims of the present review are (i) to provide the reader with a short, but comprehensive review of the current literature linking mitochondrial dysfunction and sarcopenia and (ii) to briefly discuss the potential mechanisms underlying the accumulation of mitochondrial dysfunction with muscle aging.

Three dimensionalCT analysis of femoral tunnel position after ACL reconstruction. A prospective study of one hundred and thirty five cases.

BACKGROUND: One of the principal causes for failure of anterior cruciate ligament reconstruction (ACL) is femoral tunnel mal-position. Several studies compare the position of femoral tunnels achieved with various techniques, with small series and using a quadrant assessment method. QUESTIONS: (1) What is the incidence of anatomical positioning of the intra-articular femoral tunnel aperture in primary ACL reconstruction in a university knee surgery? (2) What are the main errors in positioning? METHODS: 3D-CT scans were performed after primary ACL reconstruction in 135 consecutive cases. The intra-articular position of the femoral tunnel aperture was analyzed using the Magnussen classification. RESULTS: The intra-articular tunnel position was deemed anatomical in 77%, intermediate in 20.8%, and non-anatomical in 2.2%. Among the mal-positioned tunnels, 54.8% were vertical, 29% were anteriorly positioned, and 16.1% were both. CONCLUSIONS: The intra articular femoral tunnel aperture was well positioned using an outside-in technique. The main error of tunnel positioning was a tunnel too vertical. LEVEL OF EVIDENCE: Level III, prospective study (case series).

Influence of physiological noise on accelerated 2D and 3D resting state functional MRI data at 7 T.

PURPOSE: Physiological noise often dominates the blood-oxygen level-dependent (BOLD) signal fluctuations in high-field functional MRI (fMRI) data. Therefore, to optimize fMRI protocols, it becomes crucial to investigate how physiological signal fluctuations impact various acquisition and reconstruction schemes at different acquisition speeds. In particular, further differences can arise between 2D and 3D fMRI acquisitions due to different encoding strategies, thereby impacting fMRI sensitivity in potentially significant ways. METHODS: The amount of physiological noise to be removed from the BOLD fMRI signal acquired at 7 T was quantified for different sampling rates (repetition time from 3300 to 350 ms, acceleration 1 to 8) and techniques dedicated to fast fMRI (simultaneous multislice echo planar imaging [EPI] and 3D EPI). Resting state fMRI (rsfMRI) performances were evaluated using temporal signal-to-noise ratio (tSNR) and network characterization based on seed correlation and independent component analysis. RESULTS: Overall, acceleration enhanced tSNR and rsfMRI metrics. 3D EPI benefited the most from physiological noise removal at long repetition times. Differences between 2D and 3D encoding strategies disappeared at high acceleration factors (6- to 8-fold). CONCLUSION: After physiological noise correction, 2D- and 3D-accelerated sequences provide similar performances at high fields, both in terms of tSNR and resting state network identification and characterization. Magn Reson Med 78:888-896, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Simultaneous measurement of T1 /B1 and pharmacokinetic model parameters using active contrast encoding (ACE)-MRI.

The aim of this study was to assess the feasibility of combining dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI) with the measurement of the radiofrequency (RF) transmit field B1 and pre-contrast longitudinal relaxation time T10 . A novel approach has been proposed to simultaneously estimate B1 and T10 from a modified DCE-MRI scan that actively encodes the washout phase of the curve with different amounts of T1 and B1 weighting using multiple flip angles and repetition times, hence referred to as active contrast encoding (ACE)-MRI. ACE-MRI aims to simultaneously measure B1 and T10 , together with contrast kinetic parameters, such as the transfer constant Ktrans , interstitial space volume fraction ve and vascular space volume fraction vp . The proposed method was tested using numerical simulations and in vivo studies with mouse models of breast cancer implanted in the flank and mammary fat pad, and glioma in the brain. In the numerical simulation study with a signal-to-noise ratio of 10, both B1 and T10 were estimated accurately with errors of 5.1 ± 3.5% and 12.3 ± 8.8% and coefficients of variation (CV) of 14.9 ± 8.6% and 15.0 ± 5.0%, respectively. Using the same ACE-MRI data, the kinetic parameters Ktrans , ve and vp were also estimated with errors of 14.2 ± 8.3% (CV = 13.5 ± 4.6%), 14.7 ± 9.9% (CV = 13.3 ± 4.5%) and 14.0 ± 9.3% (CV = 14.0 ± 4.5%), respectively. For the in vivo tumor data from 11 mice, voxel-wise comparisons between ACE-MRI and DCE-MRI methods showed that the mean differences for the five parameters were as follows: ΔKtrans  = 0.006 (/min), Δve  = 0.016, Δvp  = 0.000, ΔB1  = -0.014 and ΔT1  = -0.085 (s), which suggests a good agreement between the two methods. When compared with separately measured B1 and T10 , and DCE-MRI estimated kinetic parameters as a reference, the mean relative errors of ACE-MRI estimation were B1  = -0.3%, T10  = -8.5%, Ktrans  = 11.4%, ve  = 14.5% and vp  = 4.5%. This proof-of-concept study demonstrates that the proposed ACE-MRI method can be used to estimate B1 and T10 , together with contrast kinetic model parameters.