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The resistance of cancer cells to therapy is responsible for the death of most patients with cancer 1 . Epithelial-to-mesenchymal transition (EMT) has been associated with resistance to therapy in different cancer cells 2 , 3 . However, the mechanisms by which EMT mediates resistance to therapy remain poorly understood. Here, using a mouse model of skin squamous cell carcinoma undergoing spontaneous EMT during tumorigenesis, we found that EMT tumour cells are highly resistant to a wide range of anti-cancer therapies both in vivo and in vitro. Using gain and loss of function studies in vitro and in vivo, we found that RHOJ—a small GTPase that is preferentially expressed in EMT cancer cells—controls resistance to therapy. Using genome-wide transcriptomic and proteomic profiling, we found that RHOJ regulates EMT-associated resistance to chemotherapy by enhancing the response to replicative stress and activating the DNA-damage response, enabling tumour cells to rapidly repair DNA lesions induced by chemotherapy. RHOJ interacts with proteins that regulate nuclear actin, and inhibition of actin polymerization sensitizes EMT tumour cells to chemotherapy-induced cell death in a RHOJ-dependent manner. Together, our study uncovers the role and the mechanisms through which RHOJ acts as a key regulator of EMT-associated resistance to chemotherapy. RHOJ regulates epithelial-to-mesenchymal-transition-associated resistance to chemotherapy by enhancing the response to replicative stress and activating the DNA damage response, enabling tumour cells to rapidly repair DNA lesions induced by chemotherapy.

Genomic profiling of carcinogen-induced skin tumors in mice provides a comprehensive characterization of their mutational landscape. Mouse models of cancers are routinely used to study cancer biology. However, it remains unclear whether carcinogenesis in mice is driven by the same spectrum of genomic alterations found in humans. Here we conducted a comprehensive genomic analysis of 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced skin cancer, the most commonly used skin cancer model, which appears as benign papillomas that progress into squamous cell carcinomas (SCCs). We also studied genetically induced SCCs that expressed G12D mutant Kras (Kras G12D) but were deficient for p53. Using whole-exome sequencing, we uncovered a characteristic mutational signature of DMBA-induced SCCs. We found that the vast majority of DMBA-induced SCCs presented recurrent mutations in Hras , Kras or Rras2 and mutations in several additional putative oncogenes and tumor-suppressor genes. Similar genes were recurrently mutated in mouse and human SCCs that were from different organs or had been exposed to different carcinogens. Invasive SCCs, but not papillomas, presented substantial chromosomal aberrations, especially in DMBA-induced and genetically induced Trp53 -mutated SCCs. Metastasis occurred through sequential spreading, with relatively few additional genetic events. This study provides a framework for future functional cancer genomic studies in mice.

A longstanding goal in regenerative medicine is to reconstitute functional tissues or organs after injury or disease. Attention has focused on the identification and relative contribution of tissue specific stem cells to the regeneration process. Relatively little is known about how the physiological process is regulated by other tissue constituents. Numerous injury models are used to investigate tissue regeneration, however, these models are often poorly understood. Specifically, for skeletal muscle regeneration several models are reported in the literature, yet the relative impact on muscle physiology and the distinct cells types have not been extensively characterised. We have used transgenic Tg:Pax7nGFP and Flk1GFP/+ mouse models to respectively count the number of muscle stem (satellite) cells (SC) and number/shape of vessels by confocal microscopy. We performed histological and immunostainings to assess the differences in the key regeneration steps. Infiltration of immune cells, chemokines and cytokines production was assessed in vivo by Luminex®. We compared the 4 most commonly used injury models i.e. freeze injury (FI), barium chloride (BaCl2), notexin (NTX) and cardiotoxin (CTX). The FI was the most damaging. In this model, up to 96% of the SCs are destroyed with their surrounding environment (basal lamina and vasculature) leaving a \"dead zone\" devoid of viable cells. The regeneration process itself is fulfilled in all 4 models with virtually no fibrosis 28 days post-injury, except in the FI model. Inflammatory cells return to basal levels in the CTX, BaCl2 but still significantly high 1-month post-injury in the FI and NTX models. Interestingly the number of SC returned to normal only in the FI, 1-month post-injury, with SCs that are still cycling up to 3-months after the induction of the injury in the other models. Our studies show that the nature of the injury model should be chosen carefully depending on the experimental design and desired outcome. Although in all models the muscle regenerates completely, the trajectories of the regenerative process vary considerably. Furthermore, we show that histological parameters are not wholly sufficient to declare that regeneration is complete as molecular alterations (e.g. cycling SCs, cytokines) could have a major persistent impact.

Background Muscle aging is associated with a consistent decrease in the ability of muscle tissue to regenerate following intrinsic muscle degradation, injury or overuse. Age‐related imbalance of protein synthesis and degradation, mainly regulated by AKT/mTOR pathway, leads to progressive loss of muscle mass. Maintenance of anabolic and regenerative capacities of skeletal muscles may be regarded as a therapeutic option for sarcopenia and other muscle wasting diseases. Our previous studies have demonstrated that BIO101, a pharmaceutical grade 20‐hydroxyecdysone, increases protein synthesis through the activation of MAS receptor involved in the protective arm of renin‐angiotensin‐aldosterone system. The purpose of the present study was to assess the anabolic and pro‐differentiating properties of BIO101 on C2C12 muscle cells in vitro and to investigate its effects on adult and old mice models in vivo. Methods The effects of BIO101 on C2C12 differentiation were assessed using myogenic transcription factors and protein expression of major kinases of AKT/mTOR pathway by Western blot. The in vivo effects of BIO101 have been investigated in BIO101 orally‐treated (50 mg/kg/day) adult mice (3 months) for 28 days. To demonstrate potential beneficial effect of BIO101 treatment in a sarcopenic mouse model, we use orally treated 22‐month‐old C57Bl6/J mice, for 14 weeks with vehicle or BIO101. Mice body and muscle weight were recorded. Physical performances were assessed using running capacity and muscle contractility tests. Results Anabolic properties of BIO101 were confirmed by the rapid activation of AKT/mTOR, leading to an increase of C2C12 myotubes diameters (+26%, P < 0.001). Pro‐differentiating effects of BIO101 on C2C12 myoblasts were revealed by increased expression of muscle‐specific differentiation transcription factors (MyoD, myogenin), resulting in increased fusion index and number of nuclei per myotube (+39% and +53%, respectively, at day 6). These effects of BIO101 were like those of angiotensin (1–7) and were abolished with the use of A779, a MAS receptor specific antagonist. Chronic BIO101 oral treatment induced AKT/mTOR activation and anabolic effects accompanied with improved physical performances in adult and old animals (maximal running distance and maximal running velocity). Conclusions Our data suggest beneficial anabolic and pro‐differentiating effects of BIO101 rendering BIO101 a potent drug candidate for treating sarcopenia and possibly other muscle wasting disorders.

Skeletal muscle regeneration after injury follows a remarkable sequence of synchronized events. However, the mechanisms regulating the typical organization of the regenerating muscle at different stages remain largely unknown. Here we show that muscle regeneration in mice lacking either CD9 or CD81 is abnormal and characterized by the formation of discrete giant dystrophic myofibres, which form more quickly in the absence of both tetraspanins. We also show that, in myoblasts, these two tetraspanins associate with the immunoglobulin domain molecule CD9P-1 (EWI-F/FPRP), and that grafting of CD9P-1-depleted myoblasts in regenerating muscles also leads to abnormal regeneration. In vitro myotubes lacking CD9P-1 or both CD9 and CD81 fuse with a higher frequency than normal myotubes. Our study unveils a mechanism preventing inappropriate fusion of myotubes that has an important role in the restitution of normal muscle architecture during muscle regeneration. The skeletal muscle has a remarkable capacity to regenerate after injury. Here Charrin et al . reveal that restoration of muscle architecture after injury requires a tight control of muscle cell fusion by the tetraspanin proteins CD9 and CD81 through their interaction with the cell surface protein CD9P-1.

Background Spinal muscular atrophy (SMA) is a neuromuscular disease caused by loss of survival of motor neuron (SMN) protein inducing progressive muscle weakness and atrophy due to motor neurons degeneration. Despite benefits of SMN restoration therapies in patients, motor defects are still persistent. We investigated the potential of BIO101, a new drug candidate promoting muscle growth by activating the protective arm of the renin‐angiotensin system through the MAS receptor, as monotherapy or in combination with the SMN‐based therapy ASO‐10‐27 (Nusinersen). Methods BIO101 was administrated daily on severe or mild Taiwanese SMA mouse models or diluted in culture medium of SMA patient‐derived myoblasts. The BIO101 effects were evaluated on severe SMA mouse model in vivo (growth, survival and motor function), ex vivo (motor neuron, neuromuscular junction maturation, skeletal muscle phenotype) and on muscle SMN expression, while motor function effects were evaluated on mild SMA mouse model. The in vitro effects on proliferation, differentiation, metabolism and SMN expression of SMA patient‐derived myoblasts were analysed. Effects of the combination of BIO101 with ASO‐10‐27 were evaluated on severe SMA mouse model, in vivo and on tissular intracellular AKT signalling and SMN expression. Results In severe SMA mice, BIO101 alone protected lateral motor neurons (+20%, p < 0.05), limited muscular atrophy (+30%, p < 0.01), accelerated maturation of muscular fibres (+70% for fast‐twitch muscles) and neuromuscular junctions (+50% of perforated clustering, p < 0.05) with more prominent effects on fast‐twitch muscles. Those adaptations led to an improvement of muscular function, significant at 7, 9 and 10 days post‐natal (+2‐fold for crossed squares and time of suspension, p < 0.01), which was also observed in mild SMA mice at 8 and 9 months of age (p < 0.01). Interestingly, BIO101 treatment also improved SMA patient‐derived myoblast differentiation (+20% myotube diameter and nuclei/myotube, p < 0.05) and anaerobic performances (ECAR, + 10%; p ≤ 0.05) without any impact on the proliferative state and aerobic capacities through MAS receptor activation. All BIO101 effects were independent of SMN protein expression. When combined with the ASO‐10‐27, BIO101 enhanced even more muscle resistance to fatigue (> 3‐fold over 27 days for time of suspension, p < 0.05) when compared with severe SMA mice treated with ASO‐10‐27 alone, without effects on survival through the activation of AKT intracellular pathway and independently of SMN protein expression. Conclusions We showed that BIO101 constitutes an efficient SMN‐independent therapy to improve muscle performance in SMA, which could open new therapeutic avenues for patients in combination with SMN‐based therapies, or as monotherapy for less severe forms.

Since December 2019, coronavirus disease 2019 (COVID-19), caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has changed our lives. Elderly and those with comorbidities represent the vast majority of patients hospitalized with severe COVID-19 symptoms, including acute respiratory disease syndrome and cardiac dysfunction. Despite a huge effort of the scientific community, improved treatment modalities limiting the severity and mortality of hospitalized COVID-19 patients are still required. Here, we compare the effectiveness of virus- and patients-centred strategies to reduce COVID-19 mortality. We also discuss the therapeutic options that might further reduce death rates associated with the disease in the future. Unexpectedly, extensive review of the literature suggests that SARS-CoV-2 viral load seems to be associated neither with the severity of symptoms nor with mortality of hospitalized patients with COVID-19. This may explain why, so far, virus-centred strategies using antivirals aiming to inhibit the viral replicative machinery have failed to reduce COVID-19 mortality in patients with respiratory failure. By contrast, anti-inflammatory treatments without antiviral capacities but centred on patients, such as dexamethasone or Tocilizumab ® , reduce COVID-19 mortality. Finally, since the spike protein of SARS-CoV-2 binds to angiotensin converting enzyme 2 and inhibits its function, we explore the different treatment options focussing on rebalancing the renin-angiotensin system. This new therapeutic strategy could hopefully further reduce the severity of respiratory failure and limit COVID-19 mortality in elderly patients.

Silencing expression of the long noncoding RNA NEAT1 prevents paraspeckle formation and sensitizes neoplastic cells to DNA-damage-induced cell death. NEAT1 expression also predicts chemotherapy response in ovarian cancer patients. In a search for mediators of the p53 tumor suppressor pathway, which induces pleiotropic and often antagonistic cellular responses, we identified the long noncoding RNA (lncRNA) NEAT1. NEAT1 is an essential architectural component of paraspeckle nuclear bodies, whose pathophysiological relevance remains unclear. Activation of p53, pharmacologically or by oncogene-induced replication stress, stimulated the formation of paraspeckles in mouse and human cells. Silencing Neat1 expression in mice, which prevents paraspeckle formation, sensitized preneoplastic cells to DNA-damage-induced cell death and impaired skin tumorigenesis. We provide mechanistic evidence that NEAT1 promotes ATR signaling in response to replication stress and is thereby engaged in a negative feedback loop that attenuates oncogene-dependent activation of p53. NEAT1 targeting in established human cancer cell lines induced synthetic lethality with genotoxic chemotherapeutics, including PARP inhibitors, and nongenotoxic activation of p53. This study establishes a key genetic link between NEAT1 paraspeckles, p53 biology and tumorigenesis and identifies NEAT1 as a promising target to enhance sensitivity of cancer cells to both chemotherapy and p53 reactivation therapy.

The accessibility to stem cells from healthy or diseased individuals, and the maintenance of their potency are challenging issues for stem cell biology. Here we report the isolation of viable and functional skeletal myogenic cells from humans up to 17 days, and mice up to 14 days post mortem, much longer beyond previous reports. Muscle stem cells are enriched in post mortem tissue, suggesting a selective survival advantage compared with other cell types. Transplantation of mouse muscle and haematopoietic stem cells regenerates tissues robustly. Cellular quiescence contributes to this cell viability where cells adopt a reversible dormant state characterized by reduced metabolic activity, a prolonged lag phase before the first cell division, elevated levels of reactive oxygen species and a transcriptional status less primed for commitment. Finally, severe hypoxia, or anoxia is critical for maintaining stem cell viability and regenerative capacity. Thus, these cells provide a useful resource for studying stem cell biology. Stem cells hold great potential for therapeutic use but their supply is limited. Latil et al. isolate muscle stem cells from human and mouse cadavers after 17 and 14 days, respectively, and show that when transplanted into mice the cells can regenerate tissues.

Age-related macular degeneration (AMD) is the commonest cause of severe visual loss and blindness in developed countries among individuals aged 60 and older. AMD slowly progresses from early AMD to intermediate AMD (iAMD) and ultimately late-stage AMD. Late AMD encompasses either neovascular AMD (nAMD) or geographic atrophy (GA). nAMD is defined by choroidal neovascularization (CNV) and hemorrhage in the subretinal space at the level of the macula. This induces a rapid visual impairment caused by the death of photoreceptor cells. Intravitreal injection of anti-vascular endothelial growth factor (VEGF) antibodies is the standard treatment of nAMD but adds to the burden of patient care. GA is characterized by slowly expanding photoreceptor, and retinal pigment epithelium (RPE) degeneration patches progressively leading to blindness. There is currently no therapy to cure GA. Late AMD continues to be an unmet medical need representing a major health problem with millions of patients worldwide. Oxidative stress and inflammation are recognized as some of the main risk factors to developing late AMD. The antioxidant formulation AREDS (Age-Related Eye Disease Studies), contains β-carotene, which has been replaced by lutein and zeaxanthin in AREDS2, are given to patients with iAMD but have a limited effect on the incidence of nAMD and GA. Thus, to avoid or slowdown the development of late stages of AMD (nAMD or GA), new therapies targeting iAMD are needed such as crocetin obtained through hydrolysis of crocin, an important component of saffron (Crocus sativus L.), and norbixin derived from bixin extracted from Bixa orellana seeds. We have shown that these apocarotenoids preserved more effectively RPE cells against apoptosis following blue light exposure in the presence of A2E than lutein and zeaxanthin. In this review, we will discuss the potential use of apocarotenoids to slowdown the progression of iAMD, to reduce the incidence of both forms of late AMD.