Sieck, Gary C.

Long‐term exposure to cigarette smoke (CS) triggers airway hyperreactivity and remodeling, effects that involve airway smooth muscle (ASM). We previously showed that CS destabilizes the networked morphology of mitochondria in human ASM by regulating the expression of mitochondrial fission and fusion proteins via multiple signaling mechanisms. Emerging data link regulation of mitochondrial morphology to cellular structure and function. We hypothesized that CS‐induced changes in ASM mitochondrial morphology detrimentally affect mitochondrial function, leading to CS effects on contractility and remodeling. Here, ASM cells were exposed to 1% cigarette smoke extract (CSE) for 48 h to alter mitochondrial fission/fusion, or by inhibiting the fission protein Drp1 or the fusion protein Mfn2. Mitochondrial function was assessed via changes in bioenergetics or altered rates of proliferation and apoptosis. Our results indicate that both exposure to CS and inhibition of mitochondrial fission/fusion proteins affect mitochondrial function (i.e., energy metabolism, proliferation, and apoptosis) in ASM cells. In vivo, the airways in mice chronically exposed to CS are thickened and fibrotic, and the expression of proteins involved in mitochondrial function is dramatically altered in the ASM of these mice. We conclude that CS‐induced changes in mitochondrial morphology (fission/fusion balance) correlate with mitochondrial function, and thus may control ASM proliferation, which plays a central role in airway health. J. Cell. Physiol. 232: 1053–1068, 2017. © 2016 Wiley Periodicals, Inc.

ABSTRACTCervical spinal hemisection at C2 (SH) removes premotor drive to phrenic motoneurons located in segments C3–C5 in rats. Spontaneous recovery of ipsilateral diaphragm muscle activity is associated with increased phrenic motoneuron expression of glutamatergic N‐methyl‐D‐aspartate (NMDA) receptors and decreased expression of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐proprionic acid (AMPA) receptors. Glutamatergic receptor expression is regulated by tropomyosin‐related kinase receptor subtype B (TrkB) signaling in various neuronal systems, and increased TrkB receptor expression in phrenic motoneurons enhances recovery post‐SH. Accordingly, we hypothesize that recovery of ipsilateral diaphragm muscle activity post‐SH, whether spontaneous or enhanced by adenoassociated virus (AAV)‐mediated upregulation of TrkB receptor expression, is associated with increased expression of glutamatergic NMDA receptors in phrenic motoneurons. Adult male Sprague‐Dawley rats underwent diaphragm electromyography electrode implantation and SH surgery. Rats were injected intrapleurally with AAV expressing TrkB or GFP 3 weeks before SH. At 14 days post‐SH, the proportion of animals displaying recovery of ipsilateral diaphragm activity increased in AAV–TrkB‐treated (9/9) compared with untreated (3/5) or AAV–GFP‐treated (4/10; P < 0.027) animals. Phrenic motoneuron NMDA NR1 subunit mRNA expression was approximately fourfold greater in AAV–TrkB‐ vs. AAV–GFP‐treated SH animals (P < 0.004) and in animals displaying recovery vs. those not recovering (P < 0.005). Phrenic motoneuron AMPA glutamate receptor 2 (GluR2) subunit mRNA expression decreased after SH, and, albeit increased in animals displaying recovery vs. those not recovering, levels remained lower than control. We conclude that increased phrenic motoneuron expression of glutamatergic NMDA receptors is associated with spontaneous recovery after SH and enhanced recovery after AAV–TrkB treatment. J. Comp. Neurol. 525:1192–1205, 2017. © 2016 Wiley Periodicals, Inc.

AimThe aim of this study was to compare passive muscle stiffness in children with cerebral palsy (CP) and children with typical development using a novel ultrasound technique: ultrasound shear wave elastography (SWE).MethodWe conducted a prospective study of 13 children with CP (six females and seven males, median age 5y 1mo [interquartile range 4y 4mo–7y 8mo]) and 13 children with typical development (six females and seven males, median age 5y 3mo [interquartile range 4y 4mo–9y 4mo]). Demographic information and physical exam measurements were obtained in addition to shear modulus measurements (passive muscle stiffness) of the lateral gastrocnemius muscle at 20° plantar flexion, 10° plantar flexion, and 0° plantar flexion using SWE.ResultsChildren with CP had significantly greater shear modulus measurements at all three foot positions (p<0.050). When the shear modulus values were normalized to the baseline value for each child, there was no significant difference between the two groups.InterpretationPassive muscle stiffness, measured without the influence of spasticity, is greater in children with CP than in children with typical development when a muscle is at slack and at stretch. When shear modulus was normalized, the results indicate that muscle in children in both groups responds similarly to passive stretch. Further work includes evaluating effect of botulinum toxin on passive muscle properties.

Previous work investigating respiratory system mechanics in mice has reported an aging-related increase in compliance and mean linear intercept ( Lm). However, these changes were assessed using only a young (2-mo-old) and old (20- and 26-mo-old) group yet were interpreted to reflect a linear evolution across the life span. Therefore, to investigate respiratory system mechanics and lung morphometry across a more complete spectrum of ages, we utilized 2 (100% survival, n = 6)-, 6 (100% survival, n = 12)-, 18 (90% survival, n = 12)-, 24 (75% survival, n = 12)-, and 30 (25% survival, n = 12)-mo-old C57BL/6 mice. We found a nonlinear aging-related decrease in respiratory system resistance and increase in dynamic compliance and hysteresis between 2- and 24-mo-old mice. However, in 30-mo-old mice, respiratory system resistance increased, and dynamic compliance and hysteresis decreased relative to 24-mo-old mice. Respiratory system impedance spectra were measured between 1–20.5 Hz at positive end-expiratory pressures (PEEP) of 1, 3, 5, and 7 cmH2O. Respiratory system resistance and reactance at each level of PEEP were increased and decreased, respectively, only in 2-mo-old animals. No differences in the respiratory system impedance spectra were observed in 6-, 18-, 24-, and 30-mo-old mice. Additionally, lungs were fixed following tracheal instillation of 4% paraformaldehyde at 25 cmH2O and processed for Lm and airway collagen deposition. There was an aging-related increase in Lm consistent with emphysematous-like changes and no evidence of increased airway collagen deposition. Accordingly, we demonstrate nonlinear aging-related changes in lung mechanics and morphometry in C57BL/6 mice.

New FindingsWhat is the central question of this study?Several rat models are commonly used to study the physiology of ageing (e.g. Fischer 344 and Brown Norway rats are recommended by the USA National Institute of Ageing). Diaphragm muscle sarcopenia (ageing‐related muscle weakness and atrophy) remains incompletely described in these rat models.What is the main finding and its importance?Diaphragm muscle sarcopenia is present in both the Fischer 344 and Brown Norway rat strains, but appears more pronounced in Fischer 344 rats.The risk for respiratory diseases increases in adults >65 years of age, which may be attributable in part to ageing‐related weakening and atrophy (i.e. sarcopenia) of the diaphragm muscle (DIAm). The mechanisms underlying DIAm sarcopenia remain unknown. Based on existing evidence, we hypothesized that sarcopenia is most evident in type IIx and/or IIb DIAm fibres, i.e. more fatigable motor units. Currently, the USA National Institute on Aging supports Fischer 344 (F344) and Brown Norway (BN) rat strains for ageing‐related research, yet DIAm sarcopenia has not been evaluated comprehensively in either strain. Thus, the present study examined DIAm sarcopenia in older adult F344 (24 months old, 50% survival) and BN rats (32 months old, 50% survival), compared with young adult (6‐month‐old) F344 and BN rats. Measurements of contractility, contractile protein concentration, fibre type distribution and fibre cross‐sectional area were obtained from midcostal DIAm strips. Maximal specific force was reduced by ∼24 and ∼13% in older F344 and BN rats, respectively. Additionally, although the cross‐sectional area of type I and IIa DIAm fibres was unchanged in both F344 and BN rats, the cross‐sectional area of type IIx and/or IIb DIAm fibres was reduced by ∼20 and ∼15% in F344 and BN rats, respectively. Thus, although there was ageing‐related DIAm weakness and atrophy, selective to type IIx and/or IIb DIAm fibres, in both F344 and BN rats, the sarcopenic phenotype was more pronounced in F344 rats.

Hypothermia/rewarming (H/R) is poorly tolerated by the myocardium; however, the underlying intracellular basis of H/R-induced cardiac dysfunction remains elusive. We hypothesized that in cardiomyocytes, H/R disrupts excitation-contraction coupling by reducing myofilament Ca2+sensitivity due to an increase in cardiac troponin I (cTnI) phosphorylation. To test this hypothesis, isolated rat cardiomyocytes (13–15 cells from 6 rats per group) were electrically stimulated to evoke both cytosolic Ca2+([Ca2+]cyto) and contractile (sarcomere shortening) responses that were simultaneously measured using an IonOptix system. Cardiomyocytes were divided into two groups: 1) those exposed to hypothermia (15°C for 2 h) followed by rewarming (35°C; H/R); or 2) time-matched normothermic (35°C) controls (CTL). Contractile dysfunction after H/R was indicated by reduced velocity and extent of sarcomere length (SL) shortening compared with time-matched controls. Throughout hypothermia, basal [Ca2+]cytoincreased and the duration of evoked [Ca2+]cytotransients was prolonged. Phase-loop plots of [Ca2+]cytovs. contraction were shifted rightward in cardiomyocytes during hypothermia compared with CTL, indicating a decrease in Ca2+sensitivity. Using Western blot, we found that H/R increases cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of cardiomyocytes due to increased cTnI phosphorylation and reduced Ca2+sensitivity.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/hypothermiarewarming-disrupts-e-c-coupling/ .