Development of small fluorescent probes for the analysis of autophagy kinetics

Increased Mitochondrial Superoxide Level Is Partially Associated With Vemurafenib-Induced Renal Tubular Toxicity

Vemurafenib (VEM) reportedly inhibits the mitochondrial respiratory chain and reduces ferrochelatase (FECH) activity, thereby causing VEM-induced renal tubular toxicity. However, the exact mechanisms underlying VEM-induced renal tubular toxicity remain unclear. In this study, we treated human renal proximal tubular epithelial cells with VEM to elucidate these mechanisms. VEM treatment for 24 h resulted in cell damage, reduced cell viability, increased lactate dehydrogenase release and elevated the production of inflammatory cytokines. Transmission electron microscopy (TEM) and fluorescence microscopy revealed accumulation and enlargement of lysosome-derived vacuoles and mitochondrial superoxide production. Although MitoTracker showed no change in the total mitochondrial volume, TEM indicated mitochondrial damage, including smaller and less visible mitochondria. Enhanced superoxide production was confirmed using mtSOX. The mitochondria-specific antioxidant XJB-5-131 partially alleviated VEM-induced superoxide production and improved cell viability, indicating the role of superoxide in VEM-induced renal tubular toxicity. The inhibition of lysosomal acidification by bafilomycin A1 did not mitigate VEM-induced cytotoxicity, suggesting potential autophagy impairment. These findings highlight that mitochondrial dysfunction and lysosomal abnormalities are significant factors in VEM-induced renal tubular toxicity, warranting further investigation into the relationship between their mechanisms, reduced FECH activity and potential renoprotective targets.

Sustained induction of autophagy enhances survival during prolonged starvation in newt cells

Salamanders demonstrate exceptional resistance to starvation, allowing them to endure extended periods without food in their natural habitats. Although autophagy, a process involving evolutionarily conserved proteins, promotes survival during food scarcity, the specific mechanism by which it contributes to the extreme starvation resistance in newt cells remains unexplored. Our study, using the newt species Pleurodeles waltl, reveals that newt primary fibroblasts maintain constant autophagy activation during prolonged cellular starvation. Unlike normal mammalian fibroblasts, where autophagosome formation increases during acute starvation but returns to baseline levels after extended periods, newt cells maintain elevated autophagosome numbers even 4 d after autophagy initiation, surpassing levels observed in nutrient-rich conditions. Unique P. waltl mTOR orthologs show reduced lysosomal localization compared with mammalian cells in both nutrient-rich and starved states. However, newt cells exhibit dephosphorylation of mTOR substrates under starvation conditions, similar to mammalian cells. These observations suggest that newts may have evolved a distinctive system to balance seemingly conflicting factors: high regenerative capacity and autophagy-mediated survival during starvation.

LIPUS Promotes Calcium Oscillation and Enhances Calcium Dependent Autophagy of Chondrocytes to Alleviate Osteoarthritis

Osteoarthritis (OA) is a degenerative disease which places an enormous burden on society, effective treatments are still limited. As a non-invasive and safe physical therapy, low-intensity pulsed ultrasound (LIPUS) can alleviate OA progression, but the underlying mechanism is not fully understood, especially the mechanical transduction between LIPUS and the organism. In this pioneering study, the biomechanical effects of LIPUS on living mice chondrocytes and living body zebrafish are investigate by using fluorescence imaging technology, to dynamically "visualize" its invisible mechanical stimuli in the form of calcium oscillations. It is also confirmed that LIPUS maintains cartilage homeostasis by promoting chondrocyte autophagy in a calcium-dependent manner. In addition, chondrocyte ion channels are screened by scRNA-seq and confirm that the mechanosensitive ion channel transient receptor potential vanilloid 4 (TRPV4) mediated the biological effects of LIPUS on chondrocytes. Finally, it is found that a combination of pharmacologically induced and LIPUS-induced Ca2+ influx in chondrocytes enhances the cartilage-protective effect of LIPUS, which may provide new insights for optimizing LIPUS in the treatment of OA.

Autophagy: A Silent Protagonist in Kidney Transplantation

Autophagy is a lysosome-dependent regulated mechanism that recycles unnecessary cytoplasmic components. It is now known that autophagy dysfunction may have a pathogenic role in several human diseases and conditions, including kidney transplantation. Both defective and excessive autophagy may induce or aggravate several complications of kidney transplantation, such as ischemia-reperfusion injury, alloimmune response, and immunosuppressive treatment and side effects. Although it is still complicated to measure autophagy levels in clinical practice, more attention should be paid to the factors that may influence autophagy. In kidney transplantation, the association of low doses of a mammalian target of rapamycin inhibitor with low doses of a calcineurin inhibitor may be of benefit for autophagy modulation. However, further studies are needed to explore the role of other autophagy regulators.

Melatonin inhibits tongue squamous cell carcinoma: Interplay of ER stress-induced apoptosis and autophagy with cell migration

Tongue squamous cell carcinoma (TSCC) occupies a high proportion of oral squamous cell carcinoma. TSCC features high lymph node metastasis rates and chemotherapy resistance with a poor prognosis. Therefore, an effective therapy strategy is needed to improve patient prognosis. Melatonin (MT) is a natural indole compound shown to have anti-tumor effects in several cancers. This study focused on the role and mechanism of MT in TSCC cells. The results of the study suggest that MT could inhibit cell proliferation in CRL-1623 cells. Western blot analysis showed the down-regulate of cyclin B1 and the up-regulate P21 protein by MT. MT was also shown to down-regulate the expression of Zeb1, Wnt5A/B, and β-catenin protein and up-regulate E-cadherin to inhibit the migration of CRL-1623 cells. MT also promoted the expression of ATF4, ATF6, Bip, BAP31 and CHOP in CRL-1623 cells leading to endoplasmic reticulum stress, and induced autophagy and apoptosis in CRL-1623 cells. Western blots showed that MT could promote the expression of Bax, LC3, and Beclin1 proteins and inhibit the expression of p62. We screened differentially expressed long non-coding RNAs (lncRNAs) in MT-treated cells and found that the expression of MALAT1 and H19 decreased. Moreover, MT inhibited tumor growth in nude mice inoculated with CRL-1623 cells. These results suggest that MT could induce autophagy, promote apoptosis, and provide a potential natural compound for the treatment of TSCC.

Induced pluripotent stem cell-based assays recapture multiple properties of human astrocytes

The majority of the population of glial cells in the central nervous system consists of astrocytes, and impairment of astrocytes causes various disorders. It is useful to assess the multiple astrocytic properties in order to understand their complex roles in the pathophysiology. Although we can differentiate human astrocytes from induced pluripotent stem cells (iPSCs), it remains unknown how we can analyse and reveal the multiple properties of astrocytes in complexed human disease conditions. For this purpose, we tested astrocytic differentiation protocols from feeder-free iPSCs based on the previous method with some modifications. Then, we set up extra- and intracellular assessments of iPSC-derived astrocytes by testing cytokine release, calcium influx, autophagy induction and migration. The results led us to analytic methods with conditions in which iPSC-derived astrocytes behave as in vivo. Finally, we applied these methods for modelling an astrocyte-related disease, Alexander disease. An analytic system using iPSC-derived astrocytes could be used to recapture complexities in human astrocyte diseases.

Real-Time Autophagic Flux Measurements in Live Cells Using a Novel Fluorescent Marker DAPRed

Autophagy is a conserved homeostatic mechanism involved in cellular homeostasis and many disease processes. Although it was first described in yeast cells undergoing starvation, we have learned over the years that autophagy gets activated in many stress conditions and during development and aging in mammalian cells. Understanding the fundamental mechanisms underlying autophagy effects can bring us closer to better insights into the pathogenesis of many disease conditions (e.g., cardiac muscle necrosis, Alzheimer's disease, and chronic lung injury). Due to the complex and dynamic nature of the autophagic processes, many different techniques (e.g., western blotting, fluorescent labeling, and genetic modifications of key autophagy proteins) have been developed to delineate autophagy effects. Although these methods are valid, they are not well suited for the assessment of time-dependent autophagy kinetics. Here, we describe a novel approach: the use of DAPRed for autophagic flux measurement via live cell imaging, utilizing A549 cells, that can visualize and quantify autophagic flux in real time in single live cells. This approach is relatively straightforward in comparison to other experimental procedures and should be applicable to any in vitro cell/tissue models. Key features • Allows real-time qualitative imaging of autophagic flux at single-cell level. • Primary cells and cell lines can also be utilized with this technique. • Use of confocal microscopy allows visualization of autophagy without disturbing cellular functions.

An Overview of Golgi Membrane-Associated Degradation (GOMED) and Its Detection Methods

Autophagy is a cellular mechanism that utilizes lysosomes to degrade its own components and is performed using Atg5 and other molecules originating from the endoplasmic reticulum membrane. On the other hand, we identified an alternative type of autophagy, namely, Golgi membrane-associated degradation (GOMED), which also utilizes lysosomes to degrade its own components, but does not use Atg5 originating from the Golgi membranes. The GOMED pathway involves Ulk1, Wipi3, Rab9, and other molecules, and plays crucial roles in a wide range of biological phenomena, such as the regulation of insulin secretion and neuronal maintenance. We here describe the overview of GOMED, methods to detect autophagy and GOMED, and to distinguish GOMED from autophagy.