Mitochondrial dynamics is a recent topic of research in the field of cardiac physiology. The study of mechanisms involved in the morphological changes and in the mobility of mitochondria is legitimate since the adult cardiomyocytes possess numerous mitochondria which occupy at least 30% of cell volume. However, architectural constraints exist in the cardiomyocyte that limit mitochondrial movements and communication between adjacent mitochondria. Still, the proteins involved in mitochondrial fusion and fission are highly expressed in these cells and could be involved in different processes important for the cardiac function. For example, they are required for mitochondrial biogenesis to synthesize new mitochondria and for the quality-control of the organelles. They are also involved in inner membrane organization and may play a role in apoptosis. More generally, change in mitochondrial morphology can have consequences in the functioning of the respiratory chain, in the regulation of the mitochondrial permeability transition pore (MPTP), and in the interactions with other organelles. Furthermore, the proteins involved in fusion and fission of mitochondria are altered in cardiac pathologies such as ischemia/reperfusion or heart failure (HF), and appear to be valuable targets for pharmacological therapies. Thus, mitochondrial dynamics deserves particular attention in cardiac research. The present review draws up a report of our knowledge on these phenomena.

Many recent studies have demonstrated the involvement of endoplasmic reticulum (ER) stress in the development of cardiac diseases and have suggested that modulation of ER stress response could be cardioprotective. Previously, we demonstrated that the deacetylase Sirtuin 1 (SIRT1) attenuates ER stress response and promotes cardiomyocyte survival. Here, we investigated whether and how autophagy plays a role in SIRT1-afforded cardioprotection against ER stress. The results revealed that protective autophagy was initiated before cell death in response to tunicamycin (TN)-induced ER stress in cardiac cells. SIRT1 inhibition decreased ER stress-induced autophagy, whereas its activation enhanced autophagy. In response to TN- or isoproterenol-induced ER stress, mice deficient for SIRT1 exhibited suppressed autophagy along with exacerbated cardiac dysfunction. At the molecular level, we found that in response to ER stress (i) the extinction of eEF2 or its kinase eEF2K not only reduced autophagy but further activated cell death, (ii) inhibition of SIRT1 inhibited the phosphorylation of eEF2, (iii) eIF2α co-immunoprecipitated with eEF2K, and (iv) knockdown of eIF2α reduced the phosphorylation of eEF2. Our results indicate that in response to ER stress, SIRT1 activation promotes cardiomyocyte survival by enhancing autophagy at least through activation of the eEF2K/eEF2 pathway.

Background: The AMP-activated protein kinase (AMPK) is a major regulator of cellular energetics which plays key role in acute metabolic response and in long-term adaptation to stress. Recent works have also suggested non-metabolic effects. Methods: To decipher AMPK roles in the heart, we generated a cardio-specific inducible model of gene deletion of the main cardiac catalytic subunit of AMPK (Ampkα2) in mice. This allowed us to avoid the eventual impact of AMPK-KO in peripheral organs. Results: Cardio-specific Ampkα2 deficiency led to a progressive left ventricular systolic dysfunction and the development of cardiac fibrosis in males. We observed a reduction in complex I-driven respiration without change in mitochondrial mass or in vitro complex I activity, associated with a rearrangement of the cardiolipins and reduced integration of complex I into the electron transport chain supercomplexes. Strikingly, none of these defects were present in females. Interestingly, suppression of estradiol signaling by ovariectomy partially mimicked the male sensitivity to AMPK loss, notably the cardiac fibrosis and the rearrangement of cardiolipins, but not the cardiac function that remained protected. Conclusion: Our results confirm the close link between AMPK and cardiac mitochondrial function, but also highlight links with cardiac fibrosis. Importantly, we show that AMPK is differently involved in these processes in males and females, which may have clinical implications for the use of AMPK activators in the treatment of heart failure.

The coronavirus transforms the cytoplasm of susceptible cells to support virus replication. It also activates autophagy-like processes, the role of which is not well understood. Here, we studied SARS-CoV-2-infected Vero E6 cells using transmission electron microscopy and autophagy PCR array. After 6–24 h post-infection (hpi), the cytoplasm of infected cells only contained double-membrane vesicles, phagophores, and phagosomes engulfing virus particles and cytoplasmic debris, including damaged mitochondria. The phagosomes interacted with the viral nucleoprotein complex, virus particles, mitochondria, and lipid droplets. The phagosomes transformed into egress vacuoles, which broke through the plasmalemma and discharged the virus particles. The Vero E6 cells exhibited pronounced virus replication at 6 hpi, which stabilized at 18–24 hpi at a high level. The autophagy PCR array tests revealed a significant upregulation of 10 and downregulation of 8 autophagic gene markers out of 84. Altogether, these results underline the importance of autophagy-like processes for SARS-CoV-2 maturation and egress, and point to deviations from a canonical autophagy response.

Ultrastructural remodelling of slow skeletal muscle fibres in creatine kinase deficient mice: a quantitative study

The extreme lethality and limited treatment options for pancreatic ductal adenocarcinoma (PDAC) underscore the urgent need for innovative therapeutic strategies. This study presents the first preclinical investigation of a cell-free gene-directed enzyme prodrug therapy (GDEPT) based on conditioned medium (CM) from placenta-derived mesenchymal stem cells (PlacMSCs) engineered to express the yeast cytosine deaminase::uracil phosphoribosyltransferase (yCD::UPRT) fusion enzyme. The CM was concentrated tenfold (cCM) and characterized by proteomics, transmission electron microscopy, and Western blotting, confirming extracellular vesicle (EV) enrichment and UPRT expression. Therapeutic efficacy was evaluated in coculture models comprising PDAC cell lines (BxPC-3, MIA PaCa-2, SU.86.86), patient-derived xenograft organoids (PDXOs), and cancer-associated fibroblasts (PCAFs). Immunocytochemistry and Western blot analyses revealed a predominant myofibroblastic CAF phenotype, characterized by strong alpha-smooth muscle actin (αSMA) expression and low interleukin-6 levels. Treatment with yCD::UPRT-PlacMSC-cCM in the presence of 5-fluorocytosine (5-FC) enabled efficient enzymatic conversion to 5-fluorouracil (5-FU), yielding 10 μg/mL from an initial 100 μg/mL of 5-FC. This resulted in robust, dose-dependent cytotoxicity (50 % to 80 % reduction in viability) across monocultures and stromal-rich cocultures, effectively overcoming PCAF-mediated drug resistance. Therapeutic response was governed primarily by tumor cell characteristics rather than PCAF heterogeneity. In PDXOs derived from two early-stage (IA, IIB) primary tumors and one metastatic lesion, 100 µL of yCD::UPRT-PlacMSC-cCM induced cytotoxicity comparable to 1 μg/mL of 5-FU, while 25 µL was insufficient to significantly reduce viability. Collectively, these findings demonstrate that yCD::UPRT-PlacMSC-cCM delivers potent, stromal-bypassing cytotoxicity in PDAC models and represents a promising cell-free therapeutic approach for this treatment-refractory cancer.