Albumin binds to uncoupler CCCP to diminish depolarization of mitochondria

Construction of a novel NIR-emissive rhodamine derivative for monitoring mitochondrial viscosity in ferroptosis

Ferroptosis, an iron-dependent programmed cell death mechanism, is mediated by distinct molecular pathways of lipid peroxidation caused by intracellular iron supplementation and glutathione synthesis inhibition that cause oxidative damage to the cell membrane. Monitoring viscosity changes of mitochondria is essential for a deeper understanding of ferroptosis, as mitochondria will be shrunk with increased membrane density and leading to drastic mitochondrial viscous changes during ferroptosis process. Thus, it is essential to explore novel and efficient fluorescent probes for monitoring viscosity in organisms. In this work, we designed and synthesized a mitochondria-targeting probe TJ-FRP for cellular viscosity measurement via fluorescence imaging method. To obtain this probe, we firstly developed a novel modifiable fluorescent π-extended xanthene dye TJ-FR by replacing the benzoic acid group with a strong electron-withdrawing perfluorobenzoic acid group at the 9-position of xanthene framework. The dye not only presents emission wavelength at 758 nm and a large stokes shift of 142 nm in water, but also the dye is low biotoxic, membrane permeable. By reaction with 4-aminobutyltriphenylphosphonium bromide, TJ-FR was converted to the mitochondria-targeting probe TJ-FRP. TJ-FRP was successfully applied for the imaging of viscosity in living cells. Especially, the probe can be applied for visualizing mitochondrial viscosity changes during various inducers-stimulated ferroptosis process in model cells. These findings suggest that this novel NIR fluorescent probe can serve as a powerful tool to monitor the viscosity in biological samples and may provide new insights for various diseases during ferroptosis.

Cloflucarban Illuminates Specificity and Context-Dependent Activation of the PINK1-Parkin Pathway by Mitochondrial Complex Inhibition

The PTEN-induced kinase 1 (PINK1)-Parkin pathway plays a vital role in maintaining a healthy pool of mitochondria in higher eukaryotic cells. While the downstream components of this pathway are well understood, the upstream triggers remain less explored. In this study, we conducted an extensive analysis of inhibitors targeting various mitochondrial electron transport chain (ETC) complexes to investigate their potential as activators of the PINK1-Parkin pathway. We identified cloflucarban, an antibacterial compound, as a novel pathway activator that simultaneously inhibits mitochondrial complexes III and V, and V. RNA interference (RNAi) confirmed that the dual inhibition of these complexes activates the PINK1-Parkin pathway. Intriguingly, we discovered that albumin, specifically bovine serum albumin (BSA) and human serum albumin (HSA) commonly present in culture media, can hinder carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-induced pathway activation. However, cloflucarban's efficacy remains unaffected by albumin, highlighting its reliability for studying the PINK1-Parkin pathway. This study provides insights into the activation of the upstream PINK1-Parkin pathway and underscores the influence of culture conditions on research outcomes. Cloflucarban emerges as a promising tool for investigating mitochondrial quality control and neurodegenerative diseases.

A novel near-infrared fluorescent probe for ultrasensitive and visual detection of mitochondrial viscosity

The development of fluorescent probes capable of detecting abnormal changes in cellular mitochondrial viscosity is of great significance, as these changes have been connected to many diseases. In this study, the conventional tetraphenylethylene (TPE) molecule was modified to fabricate a novel near-infrared fluorescent, TTPB, which was then used to measure the mitochondrial viscosity. Due to the introduction of TPE and pyridine groups, TTPB had an AIE effect and mitochondrial targeting function. Meanwhile, TTPB was extremely sensitive to variations in viscosity for the twisted intramolecular charge transfer (TICT) phenomenon. The logarithm of fluorescence intensity (logI620) of the probe demonstrated an excellent linear connection with the logarithm of viscosity (logη) in the viscosity range of 1.2 ∼ 956.0 cP, indicating the probe could quantitatively detect viscosity. Moreover, TTPB was able to visually track autophagy in addition to detecting the mitochondrial viscosity in the inflammatory cell model. These results showed that the probe was anticipated to be employed for the early diagnosis of related diseases.

Extracellular flux analysis in intact cardiac tissue slices-A novel tool to investigate cardiac substrate metabolism in mouse myocardium

AIM

Cardiac pathologies are accompanied by alterations in substrate metabolism, and extracellular flux analysis is a standard tool to investigate metabolic disturbances, especially in immortalized cell lines. However, preparations of primary cells, such as adult cardiomyocytes require enzymatic dissociation and cultivation affecting metabolism. Therefore, we developed a flux analyzer-based method for the assessment of substrate metabolism in intact vibratome-sliced mouse heart tissue.

METHODS

Oxygen consumption rates were determined using a Seahorse XFe24-analyzer and "islet capture plates." We demonstrate that tissue slices are suitable for extracellular flux analysis and metabolize both free fatty acids (FFA) and glucose/glutamine. Functional integrity of tissue slices was proven by optical mapping-based assessment of action potentials. In a proof-of-principle approach, the sensitivity of the method was tested by analyzing substrate metabolism in the remote myocardium after myocardial infarction (I/R).

RESULTS

Here, I/R increased uncoupled OCR compared with sham animals indicating a stimulated metabolic capacity. This increase was caused by a higher glucose/glutamine metabolism, whereas FFA oxidation was unchanged.

CONCLUSION

In conclusion, we describe a novel method to analyze cardiac substrate metabolism in intact cardiac tissue slices by extracellular flux analysis. The proof-of-principle experiment demonstrated that this approach has a sensitivity allowing the investigation of pathophysiologically relevant disturbances in cardiac substrate metabolism.

Involvement of necroptosis in the selective toxicity of the natural compound (±) gossypol on squamous skin cancer cells in vitro

Cutaneous basal and squamous cell carcinoma reflect the first and second most common type of non-melanoma skin cancer, respectively. Especially cutaneous squamous cell carcinoma has the tendency to metastasize, finally resulting in a rather poor prognosis. Therapeutic options comprise surgery, radiation therapy, and a systemic or targeted chemotherapy. There are some good treatment results, but overall, the response rate of newly developed drugs is still modest. Drug repurposing represents an alternative approach where already available and clinically approved substances are used, which originally intended for other clinical benefits. In this context, we tested the effect of the naturally occurring polyphenolic aldehyde (±) gossypol with concentrations between 1 and 5 µM on the invasive squamous cell carcinoma cell line SCL-1 and normal human epidermal keratinocytes. Gossypol treatment up to 96 h resulted in a selective cytotoxicity of SCL-1 cells (IC50: 1.7 µM, 96 h) compared with normal keratinocytes (IC50: ≥ 5.4 µM, 96 h) which is mediated by mitochondrial dysfunction and finally leading to necroptotic cell death. Taken together, gossypol shows a high potential as an alternative anticancer drug for the treatment of cutaneous squamous cell carcinoma.

Dynamic Regulation of Mitochondrial [Ca2+] in Hippocampal Neurons

While neuronal mitochondria have been studied extensively in their role in health and disease, the rules that govern calcium regulation in mitochondria remain somewhat vague. In the present study using cultured rat hippocampal neurons transfected with the mtRCaMP mitochondrial calcium sensor, we investigated the effects of cytosolic calcium surges on the dynamics of mitochondrial calcium ([Ca²⁺]m). Cytosolic calcium ([Ca²⁺]c) was measured using the high affinity sensor Fluo-2. We recorded two types of calcium events: local and global ones. Local events were limited to a small, 2–5 µm section of the dendrite, presumably caused by local synaptic activity, while global events were associated with network bursts and extended throughout the imaged dendrite. In both cases, cytosolic surges were followed by a delayed rise in [Ca²⁺]m. In global events, the rise lasted longer and was observed in all mitochondrial clusters. At the end of the descending part of the global event, [Ca²⁺]m was still high. Global events were accompanied by short and rather high [Ca²⁺]m surges which we called spikelets, and were present until the complete decay of the cytosolic event. In the case of local events, selective short-term responses were limited to the part of the mitochondrial cluster that was located directly in the center of [Ca²⁺]c activity, and faded quickly, while responses in the neighboring regions were rarely observed. Caffeine (which recruits ryanodine receptors to supply calcium to the mitochondria), and carbonyl cyanide m-chlorophenyl hydrazine (CCCP, a mitochondrial uncoupler) could affect [Ca²⁺]m in both global and local events. We constructed a computational model to simulate the fundamental role of mitochondria in restricting calcium signals within a narrow range under synapses, preventing diffusion into adjacent regions of the dendrite. Our results indicate that local cytoplasmic and mitochondrial calcium concentrations are highly correlated. This reflects a key role of signaling pathways that connect the postsynaptic membrane to local mitochondrial clusters.

An ultrasensitive lipid droplet-targeted NIR emission fluorescent probe for polarity detection and its application in liver disease diagnosis

Compared to normal cells, cancer cells require more energy supply during proliferation and metabolism. In living cells, in addition to mitochondria, lipid droplets are also an important organelle for providing energy. Studies have shown that the number and distribution of lipid droplets change significantly during the production of lesions in cells. At this stage, the predisposing factors for the development of cellular lesions are not clear, thus leading to limitations in the early diagnosis and treatment of diseases such as liver injury, fatty liver, and hepatitis. To meet the urgent challenge, we used a near-infrared emission fluorescent probe SSR-LDs based on the intramolecular charge transfer effect (ICT) to detect polarity changes within intracellular lipid droplets. The probe SSR-LDs has ultra-sensitive polarity sensitivity, excellent chemical stability and photo-stability. In addition, by comparing normal and cancer cells through cell imaging experiments, we found that the robust probe has the ability to sensitively monitor the changes in lipid droplet polarity in the living cells. More importantly, using the constructed fluorescent probe, we have achieved an in vitro fluorescence detection of liver injury and fatty liver, and the detection of hepatitis at the in vivo level. The unique fluorescent probe SSR-LDs is expected to serve as a powerful tool for the medical diagnosis of diseases related to lipid droplet polarity.