Acid‐sensing ion channel 1a (ASIC1a) is well‐known to play a major pathophysiological role during brain ischemia linked to acute acidosis of ~pH 6, whereas its function during physiological brain activity, linked to much milder pH changes, is still poorly understood. Here, by performing live cell imaging utilizing Na+ and Ca2+ sensitive and spatially specific fluorescent dyes, we investigated the role of ASIC1a in cytosolic Na+ and Ca2+ signals elicited by a mild extracellular drop from pH 7.4 to 7.0 and how these affect mitochondrial Na+ and Ca2+ signaling or metabolic activity. We show that in mouse primary cortical neurons, this small extracellular pH change triggers cytosolic Na+ and Ca2+ waves that propagate to mitochondria. Inhibiting ASIC1a with Psalmotoxin 1 or ASIC1a gene knockout blocked not only the cytosolic but also the mitochondrial Na+ and Ca2+ signals. Moreover, physiological activation of ASIC1a by this pH shift enhances mitochondrial respiration and evokes mitochondrial Na+ signaling even in digitonin‐permeabilized neurons. Altogether our results indicate that ASIC1a is critical in linking physiological extracellular pH stimuli to mitochondrial ion signaling and metabolic activity and thus is an important metabolic sensor.

Cultured meat (also referred to as cultivated meat or cell-based meat)—CM—is fabricated through the process of cellular agriculture (CA), which entails application of bioengineering, i.e., tissue engineering (TE) principles to the production of food. The main TE principles include usage of cells, grown in a controlled environment provided by bioreactors and cultivation media supplemented with growth factors and other needed nutrients and signaling molecules, and seeded onto the immobilization elements—microcarriers and scaffolds that provide the adhesion surfaces necessary for anchor-dependent cells and offer 3D organization for multiple cell types. Theoretically, many solutions from regenerative medicine and biomedical engineering can be applied in CM-TE, i.e., CA. However, in practice, there are a number of specificities regarding fabrication of a CM product that needs to fulfill not only the majority of functional criteria of muscle and fat TE, but also has to possess the sensory and nutritional qualities of a traditional food component, i.e., the meat it aims to replace. This is the reason that bioengineering aimed at CM production needs to be regarded as a specific scientific discipline of a multidisciplinary nature, integrating principles from biomedical engineering as well as from food manufacturing, design and development, i.e., food engineering. An important requirement is also the need to use as little as possible of animal-derived components in the whole CM bioprocess. In this review, we aim to present the current knowledge on different bioengineering aspects, pertinent to different current scientific disciplines but all relevant for CM engineering, relevant for muscle TE, including different cell sources, bioreactor types, media requirements, bioprocess monitoring and kinetics and their modifications for use in CA, all in view of their potential for efficient CM bioprocess scale-up. We believe such a review will offer a good overview of different bioengineering strategies for CM production and will be useful to a range of interested stakeholders, from students just entering the CA field to experienced researchers looking for the latest innovations in the field.

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Impaired phosphodiesterase (PDE) function and mitochondrial Ca2+ - [Ca2+]m signaling leads to cardiac failure, ischemic damage and dysfunctional learning and memory. Yet, a causative link between these pathways is unknown. Here, we fluorescently monitored [Ca2+]m transients in hippocampal neurons evoked by caffeine followed by depolarization. [Ca2+]m efflux was apparent in WT but diminished in neurons deficient in the mitochondrial Na+/Ca2+ exchanger NCLX. Surprisingly, neuronal depolarization-induced Ca2+ transients alone failed to evoke strong [Ca2+]m efflux in WT neurons. Caffeine is also a PDE inhibitor. Pretreatment with the PDE2 inhibitor Bay 60-7550 rescued [Ca2+]m efflux triggered by neuronal depolarization. Inhibition of PDE2 acted by diminishing the Ca2+ dependent reduction of mitochondrial cAMP, thereby promoting NCLX phosphorylation. Selective PDE2 inhibition also enhanced [Ca2+]m efflux triggered by neuromodulators. We found that protection of neurons against excitotoxic insults, conferred by PDE2 inhibition, was diminished in NCLX KO neurons, thus is NCLX dependent. Finally, administration of Bay 60-7550 enhanced new object recognition learning in WT but not in NCLX KO mice. Our results identify a long-sought link between PDE and [Ca2+]m signaling thereby providing new therapeutic targets.