Why sedentary life is detrimental while physical activity is so beneficial for healthy ageing? Which are the signalling pathways that control muscle mass/function and reverberate to whole body affecting disease onset and mortality?
According to World Health Organization, sedentary life is the fourth leading risks of global mortality while physical activity improves quality of life and survival (healthy ageing). In the last years my lab greatly contributes to identify the molecular details that regulate muscle mass and longevity pathways. We are interest in understanding the signaling pathways that control protein synthesis and degradation, organelle biogenesis, autophagy, transcriptional regulation and how these systems reverberate from muscles to whole body for a healthy ageing. To reach this goal we use a multidisciplinary approach including genetics, in vivo imaging, physiology, molecular biology and biochemistry at single cell as well as tissue level.
Skeletal muscles constitute the 40-50% of total body mass and play a critical role not only in locomotion and breathing but also in whole body metabolism. Skeletal muscles control glucose and lipid metabolism and are the major source of aminoacids during catabolic conditions such as cancer, cardiac failure, infections, burn injury and ageing. These acquired diseases as well as inherited muscle disorders are characterised by muscle wasting and weakness. People that face with muscle loss show an increased morbidity and mortality. Despite the aetiology, the pathogenetic mechanisms that induce muscle wasting are often shared by different diseases. The abnormal upregulation of protein breakdown systems, reduction of protein synthesis, impairment or drop of muscle stem cell and decreased regenerative capacity of muscle are believed to be responsible for muscle loss in ageing and many diseases. Importantly, a new concept is emerging from recent studies that consider the metabolic adaptations occurring in skeletal muscles as disease modifier/controller. For instance, changes in muscle metabolism override a mitochondrial problem in the heart and prevent the onset of dilated cardiomyopathy and heart failure.
Sandri group was the first to identify that protein breakdown requires a transcriptional-dependent program that regulates key and rate limiting enzymes of ubiquitin-proteasome and autophagy-lysosome systems. His lab also identified several unexpected links between pathways that control protein synthesis and muscle growth with the signalling of protein degradation. This knowledge was translated to several inherited muscle dystrophies and our lab was the first to identify autophagy impairment as a pathogenetic mechanism of muscle loss in Duchenne and Ullrich muscle dystrophies. Importantly, a nutritional-based clinical trial successfully showed that reactivation of autophagy is beneficial in patients. The connection between energy, mitochondria and nuclear programs that contrl the metabolic flexibility during exercise and how relevant is mitochondrial biogenesis and mitophagy are also topics in which Sandri lab greatly contributed in the last years. We now wish to understand how muscle programs that are under nutritional and physical activity/inactivity regulation systemically reverberate affecting distal organ function and life span.
Signaling pathways that control muscle mass, metabolism and longevity
Left Panel: Confocal microscopy analysis shows that autophagosome vesicles (green) are induced in isolated muscle fibres during starvation and are distributed throughout the fibres. Middle Panel: Confocal microscopy analysis shows that autophagosome vesicles (green) are induced by FoxO3 in isolated muscle fibres and some engulf mitochondria (red). Single fibres from the FDB muscle were transfected with LC3-GFP (an autophagosome marker) mitoRed (mitochondrial marker) and FoxO3 and examined by confocal microscopy. Co-transfection of skeletal muscles with FoxO3 and LC3-GFP was found to induce a large number of green fluorescent dots in myofibres and concomitantly a reduction in number and size of mitochondria (red). Furthemore, some mitochondria are inside autophagosome (yellow stain in merge picture) suggesting that FoxO3 induces reduction in mitochondria via mitophagy. Right Panel: Adult skeletal muscles transfected by electroporation with TFEB-GFP and stained for dystrophin (red). Exercise induced a nuclear localization of TFEB to induce metabolic flexibility.
Signalling pathways that control protein breakdown and protein synthesis
Skeletal muscles constitute the 40-50% of total body mass and play a critical role not only in locomotion but also in whole body metabolism. Many diseases, including inherited or acquired disorders, alter muscle function leading to muscle wasting and weakness. People that face with muscle loss show an increased morbidity and mortality. Despite the different aetiology of muscle loss, the pathogenetic mechanisms that induce muscle wasting are often shared by different diseases. In fact, skeletal muscle serves as the major protein reservoir of the body from which amino acids can be mobilized for liver gluconeogenesis or new protein synthesis and energy source of different tissues. Consequently, upon food deprivation and in many systemic catabolic disease states, including AIDS, cancer, burn injury, diabetes, cardiac and renal failure, there is a generalized muscle wasting, which results primarily from increased breakdown of muscle proteins, although protein synthesis also falls in most of these conditions. In all these systemic catabolic states, the loss of muscle mass involves a common pattern of transcriptional changes, including induction of genes for protein degradation, and decreased expression of various genes for growth-related and energy-yielding processes. We have termed this group of co-ordinately regulated genes, “atrogenes”. Between these genes there are several belonging to important cellular function such as energy production, chromatin remodelling, transcription, proteolysis, protein synthesis and metabolism. In the atrophying muscles, the ubiquitin-proteasome and autophagy-lysosome systems are activated and catalyze the degradation of the bulk of muscle proteins, including myofibrillar components, and of organelles. We were the first to identify the transcription factor involved in regulation of muscle atrophy program. The key mediators of this catabolic response during atrophy are the FoxO family of transcription factors, whose activity is suppressed during growth by phosphorylation by AKT, but whose expression and dephosphorylation rises in catabolic states (Sandri et al., Cell 2004). FoxO transcription factors are crucial during muscle loss and they coordinate the activation of the two most important proteolytic system of the cell, the autophagy-lysosome and ubiquitin-proteasome (Mammucari et al., Cell Metab. 2007; Milan et al., Nature Communications 2015), because FoxOs regulate the expression of few rate-limiting enzymes of the two proteolytic systems. The new frontier of my lab is the identification of novel FoxO downstream targets that orchestrate the autophagy-lysosome network and ubiquitin-proteasome system.
Role of physical activity, mitochondrial dynamics (biogenesis and fragmentation) and energy balance in muscle mass regulation and healthy ageing
According to the Worlds Health Organization (WHO) inactivity has been identified as the fourth leading risk factor for global mortality (WHO, 2009). Strikingly, sedentary behaviour has a deleterious effect on human health that has been quantified to be similar to smoking and severe obesity. Conversely, the impact of physical activity on human health is profound and unequivocal. Indeed, physical activity and exercise counteract the onset of the most deadly chronic diseases, including cardiovascular diseases, metabolic diseases, cancer, pulmonary disease, immune dysfunction, musculoskeletal and neurological disorders. Not surprising, an active life is important for a healthy ageing and to promote longevity. Despite the indisputable evidence of the myriad physiological benefits conferred by regular exercise, the exact molecular mechanisms by which physical activity promotes human health and conversely, inactivity causes disease onset remain poorly understood.
We have shown that both autophagy and mitochondrial dynamics are physical activity sensors. In fact, inactivity reduces while exercise stimulates these systems. By using genetic approaches (e.g. generation of muscle specific and inducible muscle specific transgenic and knockout mice), we have found that mitochondrial quality control (e.g. mitophagy, mitochondrial fusion and fission) plays an important role not only in muscle mass regulation but also in distal organs function and longevity. For instance, autophagy is reduced in myofibers and muscle stem cells during ageing in humans (Garcia Prat et al. Nature 2016; Carnio et al. Cell Reports 2014), and specific inhibition of autophagy in myofibers induces a precocious ageing phenotype that ultimately reduces lifespan of mice.
Moreover, we have found that mitochondrial fusion and fission proteins are downregulated during unhealthy ageing and are induced by exercise both in humans and mice. By using inducible muscle specific knockout mice, we have recently shown that inhibition of mitochondrial fusion in skeletal muscle is sufficient to activate senescence programs in epithelial tissues (e.g. skin, liver and gut), to trigger a systemic inflammatory response and to cause a premature death. Mechanistically, mitochondrial dysfunction in muscles triggers the expression and the secretion of the hormone FGF21 that induces premature ageing, systemic inflammation and the precocious death (Tezze et al. Cell Metabolism 2017). Altogether these and other findings confirm that muscles by secreting hormones, metabolites and miRNAs alter distal tissue function/metabolism ultimately affecting disease onset/proregression and organism survival. The next step is to identify which are these pro-ageing factors, to develop diagnostic tools for biological age determination and to generate new therapeutic approaches (drugs, diet, exercise) to promote healthy ageing.
Finally, we have dissected how exercise ameliorate glucose homeostasis and mitochondrial activity. In fact, we have shown that exercise stimulates the calcium dependent phosphatase, calcineurin, that dephosphorylates and activates the transcription factor TFEB. By generating Inducible muscle specific TFEB transgenic and knockout mice we showed that TFEB upregulates glucose transporters for glucose uptake and simultaneously, induces mitochondrial biogenesis independently of PGC1a (Mansueto et al. Cell Metabolsim 2017).
Role of proteostasis in inherited muscle diseases and identification of biomarkers to monitor autophagy in muscles
Proteostasis means the cellular systems that control the quality of the proteins. Among them the degradative processes such as ubiquitin proteasome and autophagy-lysosome play a critical role. Autophagy is a dynamic process regulated by around 30 proteins which commit membranes to engulf portion of cytoplasm, organelles and proteins for delivery to lysosome system to degrade the sequestered components. This process is highly conserved and is important for removal of damaged organelles, toxic proteins and pathogens. Furthermore, autophagy is critical for cell survival, during nutrient deprivation, providing alternative energy sources, but it is detrimental when is either massively activated or strongly inhibited. We found that both excessive induction of autophagy (self eating) and inhibition of basal autophagy result in muscle loss even. Because the morphological alterations of the muscle specific autophagy knockout mice are reminiscent of features present in some myopathies/dystrophies we investigated the role of autophagy in inherited muscle diseases. Importantly, we found that collagen VI myopathies, i.e. Ullrich and Bethlem dystrophy, Duchenne dystrophy and the lysosomal storage disease, i.e. Pompe and Danon diseases, are characterized by an autophagy defect. Importantly, when we restore the autophagy flux via nutritional, genetic or pharmacological approaches we greatly ameliorate muscle force and structure in these inherited diseases (Grumati et al. Nat Med. 2010). This result allow us to set up the first clinical trial based on a nutritional approach in Bethlem patients that was successful. The next step is to develop specific drug for autophagy reactivation and to develop blood biomarkers that mirror the autophagy status of muscles.
Finally, we have shown that inhibition of a muscle specific ubiquitin ligase (atrogin1) resulted in a cardiomyopathy that was consequent to autophagy impairment. Proteomic analyses identified the mechanistic link between ubiquitin proteasome, autophagy system and heart failure. Indeed, atrogin1 regulates the half life of a critical protein of autophagy-lysosome fusion whose accumulation resulted in autophagy impairment and cardiomyocyte apoptotic cell death (Taglia et al. Journal Clinical Investigation 2014). The identification of the cross-talk between these two proteolytic systems as well as with the protein synthesis is a major goal of my lab.
- Mammucari C, Milan G., Romanello V., Masiero E., Ruediger R., Del Piccolo P., Burden S.J., Di Lisi R., Sandri C., Zhao J., Goldberg A.L., Schiaffino S., Sandri M. FoxO3 controls autophagy in skeletal muscle in vivo. Cell Metab. 2007 Dec;6(6):458-71.
- Masiero E, Agatea L, Mammucari C, Blaauw B, Loro E, Komatsu M, Metzger D, Reggiani C, Schiaffino S, Sandri M. Autophagy is required to maintain muscle mass. Cell Metab. 2009, Dec;10(6):507-15,
- Grumati P, Coletto L, Sabatelli P, Cescon M, Angelin A, Bertaggia E, Blaauw B, Urciolo A, Tiepolo T, Merlini L, Maraldi NM, Bernardi P, Sandri M#, Bonaldo P#. Autophagy is defective in collagen VI muscular dystrophies and its reactivation rescues myofiber degeneration. Nat Med. 2010, Nov;16(11):1313-20. # Co-corresponding Authors.
- Sartori R., Schirwis E., Blaauw B., Bortolanza S., Zhao J., Enzo E., Stantzou E., Mouisel E., Toniolo L., Ferry A., Stricker S., Goldberg AL., Dupont S., Piccolo S., Amthor H., and Sandri M. BMP signaling controls muscle mass. Nat. Genet. 2013 Nov;45(11):1309-18.
- Carnio S, LoVerso F, Baraibar MA, Longa E, Khan MM, Maffei M, Reischl M, Canepari M, Loefler S, Kern H, Blaauw B, Friguet B, Bottinelli R, Rudolf R, and Sandri M. Impairment of autophagy in muscle induces neuro-muscular junction degeneration and precocius ageing. Cell Reports. 2014 Sep 11;8(5):1509-21.
- Zaglia T, Milan G, Ruhs A, Franzoso M, Bertaggia E, Pianca N, Carpi A, Carullo P, Pesce P, Sacerdoti D, Sarais C, Catalucci D, Krüger M, Mongillo M, and Sandri M. Inhibition of the ubiquitin ligase Atrogin-1/MAFbx impairs CHMP2B turnover blocks autophagy flux and causes cardiomyopathy. J Clin Invest. 2014 Jun 2;124(6):2410-24.
- Milan G, Romanello V, Pescatore F, Armani A, Paik JH, Frasson F, Seydel A, Zhao J, Abraham R, Goldberg AL, Blaauw B,. DePinho RA, Sandri M. Regulation of autophagy and ubiquitin-proteasome system by FoxO transcriptional network during muscle atrophy. Nat. Comm. 2015 2015 Apr 10;6:6670
- García-Prat L, Martínez-Vicente M, Perdiguero E, Ortet L, Rodríguez-Ubreva J, Rebollo E, Ruiz-Bonilla V, Gutarra S, Ballestar E, Serrano AL, Sandri M, Muñoz-Cánoves P. Autophagy maintains stemness by preventing senescence. Nature. 2016 Jan 7;529(7584):37-42.
- Mansueto M, Armani A, Viscomi C, D’Orsi L, De Cegli R, Polishchuk EV, Lamperti C, Di Meo I, Romanello V, Marchet S, Saha PK, Zong H, Blaauw B, Solagna F, Tezze C, Grumati P, Bonaldo P, Pessin JE, Zeviani M, Sandri M*#, Ballabio A*. Transcription Factor EB Controls Metabolic Flexibility During Exercise. Cell Metab. 2017 Jan 10;25(1):182-196. doi: 10.1016/j.cmet.2016.11.003 * Co-corresponding Authors; #Lead Corresponding author
- Tezze C, Romanello V, Desbats MA, Fadini GP, Albiero M, Favaro G, Ciciliot S, Soriano ME, Morbidoni V, Cerqua C, Loefler S, Kern H, Franceschi C, Salvioli S, Conte M, Blaauw B, Zampieri S, Salviati L, Scorrano L, Sandri M. Age-Associated Loss of OPA1 in Muscle Impacts Muscle Mass, Metabolic Homeostasis, Systemic Inflammation, and Epithelial Senescence. Cell Metab. 2017 Jun 6;25(6):1374-1389.
- MD: University of Padova, Italy (1996)
- Specialist in Clinical Pathology: University of Padova (2001).
- Postdoc: Department of Cell Biology, Harvard Medical School, Boston, USA (2002-2005).
- Telethon Scientist, Dulbecco Telethon Institute at Venetian Institute of Molecular Medicine (VIMM), Padova, Italy (2005-2015).
- Assistant Professor: Department of Biomedical Science, Medical School, University of Padova, Padova, Italy (2006- 2013).
- Associate Professor: Department of Biomedical Science, Medical School, University of Padova, Padova, Italy (2013- 2014).
- Principal Investigator at Telethon Institute of Genetics and Medicine (TIGEM), Napoli, Italy (2013-2015).
- Adjunct Professor: Department of Medicine, Faculty of Medicine, McGill University, Montreal, Canada (since 2011).
- Chair of the Myology Centre (CirMYO): University of Padova, Padova, Italy (2013-present).
- Full Professor: Department of Biomedical Science, Medical School, University of Padova, Padova, Italy (since 2014)
- 2005-2010 – Telethon Career Award.
- 2003 – “Terme Euganee Award” on Skeletal Muscle Regeneration, Reconstruction and Engineering.
- 1997 – “Luigi Casati” prize, conferred by National Academy of Lincei.