Abnormal formation and organization of collagen network is commonly observed in many organ pathologies, but analytical techniques able to reveal the collagen biodistribution are still lacking. In this study, Fourier-transform infrared (FTIR) spectroscopy has been used to analyze type I, III, IV, V, and VI collagens, the most important compounds of connective tissues. A robust classification of 30 FTIR spectra per collagen type could be obtained by using a combination of four spectral intervals [nu(C=O) absorption of amide I (1,700-1,600 cm(-1)), delta(CH(2)), and delta(CH(3)) absorptions (1,480-1,350 cm(-1)), nu(C-N), and delta(N-H) absorptions of amide III (1,300-1,180 cm(-1)), and nu(C-O) and nu(C-O-C) absorptions of carbohydrate moieties (1,100-1,005 cm(-1))]. Then, a submolecular justification of this classification model was sought using a curve fitting analysis of the four spectral intervals. Results demonstrated that every spectral interval used for the classification contained highly discriminant absorption bands between all collagen types (multivariate analysis of variance, p < 0.01; Dunnett's T3 post hoc test, p < 0.05). All conditions seem thus joined to make FTIR spectroscopy and imaging major tools for implementing innovative methods in the field of molecular histology, which would be very helpful for the diagnosis of a wide range of pathologies.

Mitochondrial dysfunction is implicated in skeletal muscle atrophy and dysfunction with aging, with strong support for an increased mitochondrial-mediated apoptosis in sedentary rodent models. Whether this applies to aged human muscle is unknown, nor is it clear whether these changes are caused by sedentary behavior. Thus, we examined mitochondrial function [respiration, reactive oxygen species (ROS) emission, and calcium retention capacity (CRC)] in permeabilized myofibers obtained from vastus lateralis muscle biopsies of healthy physically active young (23.7±2.7 yr; mean±SD) and older (71.2±4.9 yr) men. Although mitochondrial ROS and maximal respiratory capacity were unaffected, the acceptor control ratio was reduced by 18% with aging, suggesting mild uncoupling of oxidative phosphorylation. CRC was reduced by 50% with aging, indicating sensitization of the mitochondrial permeability transition pore (mPTP) to apoptosis. Consistent with the mPTP sensitization, older muscles showed a 3-fold greater fraction of endonuclease G (a mitochondrial proapoptotic factor)-positive myonuclei. Aged muscles also had lower mitophagic potential, based on a 43% reduction in Parkin to the voltage-dependent anion channel (VDAC) protein ratio. Collectively, these results show that mitochondrial-mediated apoptotic signaling is increased in older human muscle and suggest that accumulation of dysfunctional mitochondria with exaggerated apoptotic sensitivity is due to impaired mitophagy.

Skeletal muscle aging is associated with a progressive decline in muscle mass and strength, a process termed sarcopenia. Evidence suggests that accumulation of mitochondrial dysfunction plays a causal role in sarcopenia, which could be triggered by impaired mitophagy. Mitochondrial function, mitophagy and mitochondrial morphology are interconnected aspects of mitochondrial biology, and may coordinately be altered with aging. However, mitochondrial morphology has remained challenging to characterize in muscle, and whether sarcopenia is associated with abnormal mitochondrial morphology remains unknown. Therefore, we assessed the morphology of SubSarcolemmal (SS) and InterMyoFibrillar (IMF) mitochondria in skeletal muscle of young (8-12wk-old) and old (88-96wk-old) mice using a quantitative 2-dimensional transmission electron microscopy approach. We show that sarcopenia is associated with larger and less circular SS mitochondria. Likewise, aged IMF mitochondria were longer and more branched, suggesting increased fusion and/or decreased fission. Accordingly, although no difference in the content of proteins regulating mitochondrial dynamics (Mfn1, Mfn2, Opa1 and Drp1) was observed, a mitochondrial fusion index (Mfn2-to-Drp1 ratio) was significantly increased in aged muscles. Our results reveal that sarcopenia is associated with complex changes in mitochondrial morphology that could interfere with mitochondrial function and mitophagy, and thus contribute to aging-related accumulation of mitochondrial dysfunction and sarcopenia.

Mitochondria are complex organelles constantly undergoing processes of fusion and fission, processes that not only modulate their morphology, but also their function. Yet the assessment of mitochondrial function in skeletal muscle often involves mechanical isolation of the mitochondria, a process which disrupts their normally heterogeneous branching structure and yields relatively homogeneous spherical organelles. Alternatively, methods have been used where the sarcolemma is permeabilized and mitochondrial morphology is preserved, but both methods face the downside that they remove potential influences of the intracellular milieu on mitochondrial function. Importantly, recent evidence shows that the fragmented mitochondrial morphology resulting from routine mitochondrial isolation procedures used with skeletal muscle alters key indices of function in a manner qualitatively similar to mitochondria undergoing fission in vivo. Although these results warrant caution when interpreting data obtained with mitochondria isolated from skeletal muscle, they also suggest that isolated mitochondrial preparations might present a useful way of interrogating the stress resistance of mitochondria. More importantly, these new findings underscore the empirical value of studying mitochondrial function in minimally disruptive experimental preparations. In this review, we briefly discuss several considerations and hypotheses emerging from this work. Mitochondria regulate critical cellular processes, from energy production to apoptosis, and measuring their function is an imperative for scientists whose research focuses on different aspects of cellular metabolism. The in-depth study of mitochondrial function in muscle Tanja Taivassalo (far left) is in the Department of Kinesiology and Montreal Neurological Institute at McGill University, with a background in Neuroscience and Exercise Physiology. Russ Hepple (second from left) is in the Department of Kinesiology and Department of Medicine at McGill University, with a background in Physiology. Martin Picard (second from right) and Gilles Gouspillou (far right) are a PhD candidate and Postdoctoral Fellow, respectively, in the Hepple and Taivassalo laboratories. Together, we are working on animal model and clinical projects aiming to better understand the role of mitochondria in skeletal muscle structure and function in health, ageing, and disease. Our recent work reveals that routine mitochondrial isolation procedures from skeletal muscle have a striking impact on mitochondrial function. This and other work is driving the continued evolution of how we study and interpret mitochondrial function.tissue is most often achieved using one of two types of preparations: isolated mitochondria, where mitochondria are extracted and purified by mechanical homogenization and differential centrifugation (Frezza et al. 2007b); or permeabilized myofibres, where the plasma membrane