Muscle-Specific Adaptations, Impaired Oxidative Capacity and Maintenance of Contractile Function Characterize Diet-Induced Obese Mouse Skeletal Muscle

BACKGROUND:The effects of diet-induced obesity on skeletal muscle function are largely unknown, particularly as it relates to changes in oxidative metabolism and morphology. PRINCIPAL FINDINGS:Compared to control fed mice, mice fed a high fat diet (HFD; 60% kcal: fat) for 8 weeks displayed increased body mass and insulin resistance without overt fasting hyperglycemia (i.e. pre-diabetic). Histological analysis revealed a greater oxidative potential in the HFD gastrocnemius/plantaris (increased IIA, reduced IIB fiber-type percentages) and soleus (increased I, IIA cross-sectional areas) muscles, but no change in fiber type percentages in tibialis anterior muscles compared to controls. Intramyocellular lipid levels were significantly increased relative to control in HFD gastrocnemius/plantaris, but were similar to control values in the HFD soleus. Using a novel, single muscle fiber approach, impairments in complete palmitate and glucose oxidation (72.8+/-6.6% and 61.8+/-9.1% of control, respectively; p<0.05) with HFD were detected. These reductions were consistent with measures made using intact extensor digitorum longus and soleus muscles. Compared to controls, no difference in succinate dehydrogenase or citrate synthase enzyme activities were observed between groups in any muscle studied, however, short-chain fatty acyl CoA dehydrogenase (SCHAD) activity was elevated in the HFD soleus, but not tibialis anterior muscles. Despite these morphological and metabolic alterations, no significant difference in peak tetanic force or low-frequency fatigue rates were observed between groups. CONCLUSIONS:These findings indicate that HFD induces early adaptive responses that occur in a muscle-specific pattern, but are insufficient to prevent impairments in oxidative metabolism with continued high-fat feeding. Moreover, the morphological and metabolic changes which occur with 8 weeks of HFD do not significantly impact muscle contractile properties

Combining Site Characterization, Monitoring and Hydromechanical Modeling for Assessing Slope Stability

Rainfall-induced landslides are a disastrous natural hazard causing loss of life and significant damage to infrastructure, farmland and housing. Hydromechanical models are one way to assess the slope stability and to predict critical combinations of groundwater levels, soil water content and precipitation. However, hydromechanical models for slope stability evaluation require knowledge about mechanical and hydraulic parameters of the soils, lithostratigraphy and morphology. In this work, we present a multi-method approach of site characterization and investigation in combination with a hydromechanical model for a landslide-prone hillslope near Bonn, Germany. The field investigation was used to construct a three-dimensional slope model with major geological units derived from drilling and refraction seismic surveys. Mechanical and hydraulic soil parameters were obtained from previously published values for the study site based on laboratory analysis. Water dynamics were monitored through geoelectrical monitoring, a soil water content sensor network and groundwater stations. Historical data were used for calibration and validation of the hydromechanical model. The well-constrained model was then used to calculate potentially hazardous precipitation events to derive critical thresholds for monitored variables, such as soil water content and precipitation. This work introduces a potential workflow to improve numerical slope stability analysis through multiple data sources from field investigations and outlines the usage of such a system with respect to a site-specific early-warning system

Impaired Macrophage and Satellite Cell Infiltration Occurs in a Muscle-Specific Fashion Following Injury in Diabetic Skeletal Muscle

<div><p>Background</p><p>Systemic elevations in PAI-1 suppress the fibrinolytic pathway leading to poor collagen remodelling and delayed regeneration of tibialis anterior (TA) muscles in type-1 diabetic Akita mice. However, how impaired collagen remodelling was specifically attenuating regeneration in Akita mice remained unknown. Furthermore, given intrinsic differences between muscle groups, it was unclear if the reparative responses between muscle groups were different.</p><p>Principal Findings</p><p>Here we reveal that diabetic Akita muscles display differential regenerative responses with the TA and gastrocnemius muscles exhibiting reduced regenerating myofiber area compared to wild-type mice, while soleus muscles displayed no difference between animal groups following injury. Collagen levels in TA and gastrocnemius, but not soleus, were significantly increased post-injury versus controls. At 5 days post-injury, when degenerating/necrotic regions were present in both animal groups, Akita TA and gastrocnemius muscles displayed reduced macrophage and satellite cell infiltration and poor myofiber formation. By 10 days post-injury, necrotic regions were absent in wild-type TA but persisted in Akita TA. In contrast, Akita soleus exhibited no impairment in any of these measures compared to wild-type soleus. In an effort to define how impaired collagen turnover was attenuating regeneration in Akita TA, a PAI-1 inhibitor (PAI-039) was orally administered to Akita mice following cardiotoxin injury. PAI-039 administration promoted macrophage and satellite cell infiltration into necrotic areas of the TA and gastrocnemius. Importantly, soleus muscles exhibit the highest inducible expression of MMP-9 following injury, providing a mechanism for normative collagen degradation and injury recovery in this muscle despite systemically elevated PAI-1.</p><p>Conclusions</p><p>Our findings suggest the mechanism underlying how impaired collagen remodelling in type-1 diabetes results in delayed regeneration is an impairment in macrophage infiltration and satellite cell recruitment to degenerating areas; a phenomena that occurs differentially between muscle groups.</p></div

Eight weeks of a high fat diet (HFD) elicits pre-diabetes.

<p>(A) Fasted body mass was assessed before experimental diet began and after 4 and 8 weeks (N = 19 CON, 20 HFD). (B) Epididymal fat mass after 8 weeks of diet intervention (N = 19 CON, N = 20 HFD). (C) Intraperitoneal glucose tolerance test (IPGTT) performed after an overnight fast (16 hrs) 1 week before harvest (N = 19 CON, N = 18 HFD). (D) Plasma insulin levels assessed 4 weeks into diet intervention (8 hr fast, N = 10) and at IPGTT 45 minute time-point (16 hr fast, N = 4). Significance is represented by * vs. CON at same time point (A–D), a or b vs. 0 weeks within diet group, and c vs. 4 weeks within diet group, p<0.005.</p

Impaired palmitate and glucose oxidation in HFD single fibers.

<p>(A) Palmitate (N = 19, average of 17 fibers/dish) and (B) glucose (N = 12 CON, N = 10 HFD, average of 23 fibers/dish) oxidation in single fibers derived from EDL and peroneus muscles was similarly impaired in mice fed a high-fat diet (HFD) compared to control (CON). Values were normalized to control values for each experiment and significance is represented by * vs. CON, p<0.005.</p

<i>In situ</i> contractile analysis reveals trend towards force decrements, yet unaltered peak force and fatigue.

<p>Relative tetanic force production [in Newtons (N) per gram (g) of wet muscle mass] in the gastrocnemius/plantaris muscle group of high-fat diet (HFD) mice compared to control (CON) was (A) not different before (Pre) or after (Post) the fatigue protocol. (B) There was no difference between diets over all frequencies used to test force production pre-fatigue, however there was a significant main effect of diet post-fatigue. (C) Contractile force, relative to initial (% initial), throughout a 2 minute low-frequency fatigue protocol was not different between diet groups. Significance is represented by * vs. CON, p<0.005.</p

Morphometric changes are muscle-specific.

<p>Serial cross-sections from control (CON, white bars in all graphs) and high fat diet (HFD, black bars in all graphs) fed mouse muscles [TA (top left only), gastrocnemius/plantaris complex (GP, all middle graphs), and soleus (all right graphs)] were examined for (A) fiber type composition, (B) area, (C) SDH stain intensity, and (D) IMCL stain intensity. Representative images of all stains used, performed on GP muscle cross-sections are shown to the left of graphs B–D with fiber type (type I, and types II- A, D, B) labeled with CON on the left and HFD on the right. (B) Metachromatic fiber type stain was used to assess fiber type. (C) SDH and (D) Oil-Red-O stains are graphically represented by arbitrary units (A.U.) of optical intensity measurements, with greater values for more intense stains and normalized to a percentage of all the control value means for each graph (% CON). All measurements were taken on an average of 51–331 total fibers/animal with a Nikon Eclipse 90i microscope (N = 3–4). Significance is represented by * vs. CON, p<0.005.</p

Necrosis of muscle fibers persists throughout muscle regeneration in Akita tibialis anterior muscle.

<p>(A) Uninjured (left), necrotic (center), and actively regenerating (right) regions of skeletal muscle are easily identified in collagen type I immunostain (green) with DAPI (blue) counterstain. Note the presence of centrally located nuclei in muscle fibers in regenerating muscle, indicative of new myofiber formation. (B) TA of diabetic mice have clearly defined areas of necrosis remaining at 10 days post-injury (significant interaction [P<0.05]; * denotes post-hoc difference). Similarly, gastrocnemius (GAS) (C) follows this pattern although not statistically significant (P = 0.21). In contrast, both WT and Akita soleus (SOL) display no areas of necrosis at 5 or 10 days post-injury (not shown). (D) Representative image of TA muscle undergoing regeneration at 10 days post-injury in WT and Akita TA. Note the distinct area of necrosis in the Akita TA. Scale bar represents 500 um.</p

Macrophage and satellite cell infiltration into necrotic muscle is impaired in Akita diabetic mice at 5 days post injury.

<p>(A) The necrotic area of the TA demonstrates a reduced number of macrophages as evidenced by less F4/80 positive cells. * denotes significant difference by t-test (p<0.05). (B) A similar, though non-significant, trend of attenuated F4/80 positive cells was observed in necrotic gastrocnemius (GAS) (P = 0.09). (C) Representative images of necrotic regions of TA and GAS immunofluorescently stained for F4/80 (red), costained for type I collagen (green) and nuclei with DAPI (blue). Satellite cells (Pax7+ cells) were also reduced in number within necrotic areas of (D) Akita TA and (E) GAS (P = 0.06). (F) Representative images of Pax7 positive cells within necrotic regions of WT and Akita TA. Scale bar represents 50 um.</p