bims-miptne 2026-06-07 papers

Curr Protoc. 2026 Jun;6(6): e70393

Measuring Calcium Efflux in Isolated Primary Mitochondria.

Ta'Aliyah M Jones, Stephen Hurst, Michael J Bround.

Mitochondrial calcium (mCa2+) homeostasis promotes oxidative metabolism within the physiological range; however, dysregulation can trigger necrotic cell death in diseases such as cardiac ischemia-reperfusion injury, muscular dystrophy, and neurodegenerative disorders, including Alzheimer's disease. It is widely understood that mitochondria exhibit rapid Ca2+ uptake primarily mediated by the mitochondrial calcium uniporter (MCU) complex, and that Ca2+ is exported via a combination of Na+/Ca2+ and H+/Ca2+ exchange processes. However, the proteins which mediate mCa2+ transport have only been partially identified. A particular challenge in determining which proteins mediate mCa2+ efflux and their relative contributions to mCa2+ homeostasis is the lack of a clear, reproducible assay for mCa2+ efflux applicable across genotypes. Here, we provide instructions for an optimized fluorometric method to measure mCa2+ efflux in isolated mitochondria that establishes robust Ca2+ efflux signals, differentiates between total and Na+-independent Ca2+ efflux modalities, and generates highly reproducible data, allowing comparisons across tissues and genotypes. © 2026 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Total Calcium Efflux Assay in Isolated Mitochondria Alternate Protocol 1: Na+-Independent Calcium Efflux Assay in Isolated Mitochondria Support Protocol 1: Isolation of Cardiac Mitochondria Support Protocol 2: Isolation of Skeletal Muscle Mitochondria Support Protocol 3: Isolation of Liver Mitochondria Support Protocol 4: Isolation of Cell Line Mitochondria Basic Protocol 2: Analysis of Calcium Efflux.

Keywords: calcium signaling; fluorimetry; mitochondria; mitochondrial calcium

DOI: https://doi.org/10.1002/cpz1.70393

J Neurochem. 2026 Jun;170(6): e70470

Calcium Buffering in Astrocytes and Its Relevance for Experimental Data Interpretation and Computational Modeling.

Kerstin Lenk, Andre Zeug, Franziska E Müller.

Astrocytic Ca2+ signaling is essential for maintaining physiological brain function, including the modulation of synaptic transmission, neurovascular coupling, and ion homeostasis. However, the spatiotemporal dynamics of astrocytic Ca2+ activity are highly sensitive to Ca2+ buffering, which shapes the amplitude, duration, and spread of cytosolic and organellar signals. These buffers include endogenous components such as cytosolic Ca2+ binding proteins, as well as organelles like the endoplasmic reticulum acting as Ca2+ stores. Additionally, exogenous buffers are introduced in experiments, including chelators, synthetic dyes, and genetically encoded Ca2+ indicators. Both types of buffers can profoundly alter experimental observations, making it challenging to accurately interpret Ca2+ dynamics. Computational modeling offers a powerful approach to separate these effects, enabling systematic exploration of how the buffering capacity of specific system components influences astrocytic intracellular and intercellular signaling. By incorporating experimental data with realistic biophysical buffering parameters, models can make predictions that are difficult to achieve empirically and help identify key parameters that shape astrocytic Ca2+ physiology. In this review, we discuss how buffering components influence astrocyte Ca2+ activity and their integration into modeling predictions. Future advances in computational modeling, combined with extensive experimental data, will be crucial for enhancing our understanding of astrocytic Ca2+ regulation and elucidating its role in health and disease.

Keywords: astrocytes; buffering; calcium; computational modeling

DOI: https://doi.org/10.1111/jnc.70470

Proc Natl Acad Sci U S A. 2026 Jun 09. 123(23): e2531128123

Polyphosphate synthesis is essential for phosphate and ATP homeostasis during nutrient upshift.

Maria L White, Julien Mortier, Lova Granqvist, Deike J Omnus, Max Louski, Nick Crang, Berent Aldikacti, Valérie Migeot, Peter Chien, Marc Hennequart, Régis Hallez, Kristina Jonas.

Inorganic polyphosphate (polyP) is a ubiquitous molecule found across all domains of life. Although implicated in diverse cellular processes, including phosphate storage, stress responses, and pathogenicity, loss of polyP synthesis typically causes only mild growth defects. Here, we demonstrate an essential physiological role for polyP synthesis during recovery from phosphate starvation, when cells transition from phosphate-limited to phosphate-replete conditions. Using a comprehensive transposon sequencing approach in Caulobacter crescentus, we identify genes conferring a fitness advantage during starvation for carbon, nitrogen, or phosphate and during subsequent recovery. We find that ppk1, encoding the polyphosphate kinase responsible for polyP synthesis, is specifically required for recovery from phosphate starvation but dispensable for entry into starvation, a result confirmed with a ppk1 deletion mutant. Mutations that reduce phosphate uptake via the phosphate-specific transport system suppress the requirement for ppk1, indicating that polyP synthesis prevents toxic accumulation of intracellular inorganic phosphate (Pi) upon refeeding. Our findings further show that buffering intracellular Pi through polyP synthesis is critical for maintaining ATP homeostasis. Together, these results define a central role for polyP synthesis in regulating intracellular phosphate balance and ATP homeostasis, thereby facilitating adaptation to fluctuating nutrient conditions.

Keywords: Caulobacter crescentus; PolyP; Ppk1; Pst system; nutrient adaptation

DOI: https://doi.org/10.1073/pnas.2531128123

Cell Metab. 2026 Jun 02. pii: S1550-4131(26)00153-1. [Epub ahead of print]38(6): 1075-1078

Mitochondria across the globe: Diverse voices, shared energy.

Ichitaro Abe, Alejandro Failde Fiestras, Maia Hjerting Ekstrand, Nahid A Khan, Kenneth Bowitz Larsen, Jason Maynes, Agata M Rudolf, Francois Singh.

Like mitochondria themselves, research on the organelle can take many shapes and sizes. This month, to coincide with the Cell Press Symposia: Multifaceted mitochondria, we are highlighting the diversity of the global mitochondria community with contributions from researchers at all career stages published across Cell Metabolism, Molecular Cell, Cell Reports, and Trends in Endocrinology & Metabolism. Together, these voices showcase the central role of mitochondrial research in metabolism, inflammation, cell biology, and much more.

DOI: https://doi.org/10.1016/j.cmet.2026.04.015