bims-miptne 2026-03-15 papers

J Physiol. 2026 Mar 10.

Robust activity-dependent mitochondrial calcium dynamics at the AIS is dispensable for action potential generation.

Mitochondria are diverse and multifaceted intracellular organelles regulating oxidative energy supply, lipid metabolism and calcium (Ca2+) signalling. In neurons the spatial sequestration of cytoplasmic Ca2+ by mitochondria plays a critical role in determining activity-dependent spine plasticity, shaping the presynaptic transmitter release characteristics and contributing to sustained action potential firing. Here, we tested the hypothesis that mitochondria at the axon initial segment (AIS) affect the microdomain cytoplasmic Ca2+ transients, thereby regulating Ca2+-dependent voltage-gated ion channels at the plasma membrane and initiation of action potentials. Using 3D electron microscopy reconstructions and virally injecting genetically encoded fluorescence indicators we visualized the ultrastructure and distribution of mitochondria selectively in thick-tufted layer 5 pyramidal neurons. We found that most mitochondria were stably clustered to the proximal AIS, while few were observed at distal sites. Simultaneous two-photon imaging of action potential-dependent cytoplasmic and mitochondrial Ca2+, combined with electrophysiological recordings showed that AIS mitochondria exhibit powerful activity-dependent cytosolic Ca2+ uptake. However, while intracellular application of the mitochondrial Ca2+ uniporter inhibitor Ru360 fully blocked mitochondrial Ca2+ import and increased the slow afterhyperpolarization duration, it did not affect action potential input-output function, action potential dynamics nor the ability to produce high-frequency burst output. Together, the results indicate that AIS mitochondria are dispensable for temporal and rate encoding, suggesting that mt-Ca2+ buffering at the AIS may be involved in non-electrical roles. KEY POINTS: Mitochondrial Ca2+ buffering controls multiple Ca2+-dependent intracellular processes and their subcellular location of the organelles defines local physiological properties in neurons. Recent studies implicate mitochondrial Ca2+ uptake in the slow afterhyperpolarization and maintenance of action potential firing. Using electron microscopy and virally delivered genetically encoded tools we examined mitochondria in the layer 5 pyramidal neuron axon initial segment (AIS), the site where action potentials initiate, and found that cytoplasmic Ca2+ influx is powerfully buffered by proximally clustered mitochondria. Electrophysiological recordings during the block of the mitochondrial calcium uniporter reveal a role in the slow afterhyperpolarization, while AIS action potential initiation and action potential waveforms are independent from mitochondria. These findings indicate AIS mitochondria under physiological conditions exert non-electrical roles.

Keywords: action potential; axon initial segment; calcium buffer; mitochondria; pyramidal neuron

DOI: https://doi.org/10.1113/JP289290

Physiol Res. 2026 Mar 13. 75(1): 175-181

Alteration of Mitochondrial Ca2+ Fluxes by Kaempferol and CGP-37157 Regulates Ca2+ Oscillations in Human Alveolar Type 2 A549 Cells.

K-C Wu, C-Y Chen, L-R Shiao, Z-H Yang, C-M Chuang, Y-M Leung.

Mitochondria participate in regulating cytosolic Ca2+ signaling by their Ca2+ handling via mitochondrial Ca2+ uniporter (MCU) and mitochondrial Na+/Ca2+ exchanger (mitoNCX). In this study, we examined how agonist-triggered cytosolic Ca2+ oscillations in human alveolar type 2 A549 cells were affected by an MCU inhibitor (MCU-i4), MCU activator (kaempferol) and mitoNCX inhibitor (CGP-37157). Whilst inhibition of MCU did not significantly repress Ca2+ oscillations, MCU activation by kaempferol considerably dampened oscillatory activities. Inhibition of mitochondrial Ca2+ efflux by CGP-37157 also suppressed Ca2+ oscillations; the suppressive effects of kaempferol and CGP 37157 were not additive. Both kaempferol and CGP-37157 caused a rise in mitochondrial matrix Ca2+ level, but their effects were not additive. Taken together, our results suggest Ca2+ oscillations in alveolar type 2 A549 cells were regulated by stimulating Ca2+ uptake into, and preventing Ca2+ efflux from, the mitochondria, with both cases resulting in disturbed Ca2+ traffic and Ca2+ accumulation in the mitochondrial matrix. Key words Mitochondria " Ca2+ oscillations " Mitochondrial Ca2+ uniporter " Mitochondrial Na+/Ca2+ exchanger " A549 cells.

Life Sci. 2026 Mar 10. pii: S0024-3205(26)00131-1. [Epub ahead of print] 124322

LETM1 deacetylation attenuates calcium overload-mediated mitochondrial injury and protects the intestine from ischemia/reperfusion damage.

Guorong Wang, Xuzi Zhao, Yunfei Feng, Fengyuan Yang, Cheng Lv, Wenjia Mi, Xinxin Zhang, Xiaofeng Tian, Jihong Yao, Guangzhi Wang.

Mitochondrial dysfunction is a central contributor to the pathogenesis of intestinal ischemia/reperfusion (I/R) injury. This dysfunction is closely linked to mitochondrial calcium overload and excessive reactive oxygen species (ROS) production, culminating in cellular apoptosis. Leucine Zipper And EF-Hand Containing Transmembrane Protein 1 (LETM1), a key regulator of mitochondrial permeability, is essential for cellular homeostasis and survival. However, the role and underlying mechanism of LETM1 in intestinal I/R injury remain poorly understood. Here, we observed that LETM1 expression was significantly downregulated in intestinal tissues following I/R. AAV9-mediated overexpression of LETM1 significantly alleviated mitochondrial dysfunction. We further found that the acetylation status at lysine 597 (K597) modulates the stability of LETM1 in Caco-2 cells. LETM1 was identified as a downstream target of mitochondrial deacetylase Sirtuin 3 (SIRT3), and its knockdown significantly impaired the protective effects of SIRT3 in vitro. Collectively, our findings provide the first evidence that LETM1 serves as a protective target against calcium overload-induced mitochondrial dysfunction and apoptosis during intestinal I/R injury. These findings highlight the therapeutic potential of targeting LETM1 deacetylation as a novel strategy for intestinal I/R injury prevention.

Keywords: Apoptosis; Intestinal I/R; LETM1; Mitochondria dysfunction; SIRT3

DOI: https://doi.org/10.1016/j.lfs.2026.124322

Clin Mol Hepatol. 2026 Mar 11.

Alcohol-induced oxidative stress triggers mitochondrial Ca²⁺ release through the permeability transition pore.

Kwangwoo Lee, Jiyoon Lee, Jihyo Byun, Eunmi Lee, Pilhan Kim, Won Kim, Won-Il Jeong.

Keywords: Mitochondrial permeability transition pore; ROS; Vesicular glutamate transporter 3; xCT

DOI: https://doi.org/10.3350/cmh.2026.0005

Int J Mol Sci. 2026 Feb 28. pii: 2279. [Epub ahead of print]27(5):

Molecular Mechanisms and Targeted Intervention Strategies of Calcium Overload in Ischemic Stroke.

Yuwei Jiang, Guijun Wang, Shengming Jiang, Youjun Wang, Qi Tian, Mingchang Li.

Ischemic stroke is a leading cause of global neurological mortality and disability, characterized by a complex pathogenesis wherein calcium overload constitutes a pivotal mechanism in neuronal and glial cell death. Following ischemia and reperfusion, excitotoxicity triggered by excessive glutamate release activates NMDA receptors and voltage-dependent calcium channels, leading to a large accumulation of intracellular Ca2+. This calcium dyshomeostasis subsequently initiates a cascade of detrimental events, including mitochondrial dysfunction, endoplasmic reticulum stress, reactive oxygen species generation, and the activation of calcium-dependent enzymes (such as calpain and phospholipase A2), ultimately culminating in cellular apoptosis or necrosis. In addition, calcium signaling imbalance is closely related to various forms of programmed cell death, such as ferroptosis and necroptosis. Research on calcium overload extends beyond neurons, with investigations in microglia and astrocytes yielding significant mechanistic insights. Although targeted interventions, encompassing calcium channel blockers, NMDA receptor antagonists, mitochondrial calcium homeostasis regulators, and calmodulin/calmodulin kinase (CaM/CaMK) inhibitors, have demonstrated preclinical progress, their clinical translation remains constrained. Future investigations should prioritize elucidating the nuanced regulatory mechanisms of calcium signaling pathways, developing highly selective and low-toxicity calcium intervention drugs, and combining multi-target treatment strategies such as neuroprotection, anti-inflammation, and tissue repair to provide theoretical basis and new solutions for the precise treatment of ischemic stroke.

Keywords: calcium overload; excitotoxicity; ischemic stroke; neuroprotection

DOI: https://doi.org/10.3390/ijms27052279

Nat Cardiovasc Res. 2026 Mar 12.

Hematopoietic expression of cIAP2 drives inflammation and heart failure after myocardial infarction.

Ischemic heart disease, driven largely by myocardial infarction (MI), remains the leading cause of mortality and morbidity. Although early suppression of post-MI inflammation improves outcomes, current therapies have limited efficacy. Here we show that the cellular inhibitor of apoptosis 2 (cIAP2), a regulator of cell death, is upregulated after MI and promotes acute inflammation and cardiac injury. Global deletion of cIAP2, or its loss through bone marrow transfer, reduced inflammatory injury and cardiac dysfunction after MI, indicating that the cardioprotective effect of cIAP2 deficiency is primarily mediated by the hematopoietic compartment. Reduced cardiac inflammation was associated with decreased splenic myeloid cell numbers due to increased cell death and elevated expression of the death-inducing factors TRAIL and TRAIL-R2/DR5. Pharmacologic degradation of cIAP proteins after MI using Smac mimetics similarly reduced cardiac inflammation and protected against injury. Together, these findings identify cIAP2 as a key hematopoietic cell-expressed regulator of survival and inflammation and support its inhibition as a potential immunotherapeutic strategy for MI.

DOI: https://doi.org/10.1038/s44161-026-00782-x