Biology subjects

Sandoval, P. Y.

Publications and source records attributed to Sandoval, P. Y..

6 recordsLinked to original sources

bioRxiv2025

MPC is a facultative pyruvate / lactate exchanger

The mitochondrial uptake of pyruvate is mediated by the MPC. In the present study, we investigated the functional properties of the carrier using genetically encoded fluorescent sensors. Mitochondrial lactate efflux was inhibited by >80% by both pharmacological and genetic MPC ablation. MPC-dependent pyruvate influx accelerated the efflux of lactate, a fingerprint of shared transport. The non-metabolized pyruvate analog oxamate, which was found to enter mitochondria solely through the MPC, was also able to trans-accelerate lactate. Reportedly, mitochondria can produce lactate under reductive stress; our findings indicate that the MPC participates in this energy/redox venting by exchanging pyruvate by lactate.

cell biology↗

bioRxiv2025

A cell-based method to assess the activity of the human sodium-coupled citrate transporter

Increasing evidence supports the human sodium-coupled citrate transporter (hNaCT) as a potential therapeutic target for metabolic syndrome, while genetic polymorphisms in hNaCT have been associated with neurological disorder. Isotopic tracers remain the primary method for evaluating citrate transport, which are labor-intensive, require dedicated equipment, and demand highly skilled personnel. Herein, we develop and validate a robust, live-cell-compatible fluorescent method to evaluate citrate transport activity mediated by hNaCT at single-cell and high-throughput levels. This method utilizes a baculoviral vector to modify HEK293 cells to co-express a genetically encoded citrate sensor (Citron1) and the hNaCT. This cell-based platform enabled real-time monitoring of citrate transport using fluorescent microscopy and standard multiwell plate reader. The present method enables the functional characterization of hNaCT gain- and loss-of-function mutation, as well as the evaluation of pharmacological inhibitors targeting citrate transport. These results demonstrate that the cell-based method reliably assesses citrate transport at a single-cell resolution and is compatible with high-throughput screening, to identify novel lead compounds for the therapeutic modulation of hNaCT.

cell biology↗

bioRxiv2024

Lactate-carried Mitochondrial Energy Overflow

We addressed the question of mitochondrial lactate metabolism using genetically-encoded sensors. The organelle was found to contain a dynamic lactate pool that leads to dose- and time-dependent protein lactylation. In neurons, mitochondrial lactate reported blood lactate levels with high fidelity. The exchange of lactate across the inner mitochondrial membrane was found to be mediated by a high affinity H+-coupled transport system involving the mitochondrial pyruvate carrier MPC. Assessment of electron transport chain activity and determination of lactate flux showed that mitochondria are tonic lactate producers, a phenomenon driven by energization and stimulated by hypoxia. We conclude that an overflow mechanism caps the redox level of mitochondria, while saving energy in the form of lactate. One Sentence SummaryMitochondrial lactate production

biochemistry↗

bioRxiv2020

Highly responsive single-fluorophoreindicator to explore lactate dynamics in high calcium environments

Lactate is an energy substrate and intercellular signaling molecule with multiple bodily functions. Lactate has physiological roles in neurogenesis, axon integrity, memory consolidation, immune response, exercise, adipose tissue lipolysis, etc, and is involved in inflammation, cancer and neurodegeneration. The FRET lactate indicator Laconic has been instrumental in the discovery of mechanisms involved in neurometabolic coupling, and has advanced the understanding of lactate transport, glycolysis and mitochondrial physiology. However, the low fluorescent response and the complex saturation kinetics of Laconic limit its use for high-throughput screening and quantitation. Using the bacterial periplasmic binding protein TTHA0766 from Thermus thermophilus, we have now developed the first single-fluorophore indicator for lactate. The sensor exhibited an intensiometric fluorescence increase of {Delta}F/F0 3.0 and a single binding site with a KD of 293 M. The fluorescence is not affected by other monocarboxylates or pH. However, it is sensitive to Ca2+ in the nanomolar range. Targeting of the sensor to the endoplasmic reticulum revealed that this organelle presents a high permeability for lactate. The functionality of the sensor in living tissue is demonstrated in the brain of Drosophila melanogaster larvae. This indicator, which we have termed CanlonicSF, is well suited to explore lactate dynamics in environments with micromolar Ca2+ or higher, such as the endoplasmic reticulum and the extracellular space.

cell biology↗

bioRxiv2019

A highly responsive pyruvate sensor reveals pathway-regulatory role of the mitochondrial pyruvate carrier MPC

Mitochondria generate ATP and building blocks for cell growth and regeneration, using pyruvate as the main substrate. Here we introduce PyronicSF, a user-friendly GFP-based sensor of improved dynamic range that enables real-time subcellular quantitation of mitochondrial pyruvate transport, concentration and flux. We report that cultured mouse astrocytes maintain mitochondrial pyruvate in the low micromolar range, below cytosolic pyruvate, which means that the mitochondrial pyruvate carrier MPC controls the decision between respiration and anaplerosis/gluconeogenesis in an ultrasensitive fashion. The functionality of the sensor in living tissue is demonstrated in the brain of Drosophila melanogaster larvae. Mitochondrial subpopulations are known to coexist within a given cell, which differ in their morphology, mobility, membrane potential, and vicinity to other organelles. The present tool can be used to investigate how mitochondrial diversity relates to metabolism, to study the role of MPC in disease, and to screen for small-molecule MPC modulators.

cell biology↗

bioRxiv2019

MCT4 is a high affinity transporter capable of exporting lactate in high-lactate environments

MCT4 is an H+-coupled transporter expressed in metastatic cancer cells, macrophages, and other highly glycolytic cells, where it extrudes excess lactate generated by the Warburg phenomenon or by hypoxia. Intriguingly, its reported Km for lactate, obtained with pH-sensitive probes, is more than an order of magnitude higher than physiological lactate. Here we examined MCT4-rich MDA-MB-231 cells using the FRET sensor Laconic and found a median Km for lactate uptake of only 1.7 mM, while parallel estimation in the same cells with a pH probe gave a Km of 27 mM. The median Km of MCT4 for lactate was 0.7 mM in MCT4-expressing HEK293 cells and 1.2 mM in human macrophages, suggesting that high substrate affinity is a robust property of the transporter. Probed with the FRET sensor Pyronic, MCT4 showed a Km for pyruvate of only 4.2 mM in MDA-MB-231 cells, as opposed to > 150 mM reported previously. We conclude that prior estimates of MCT4 affinity based on pH probes were severely biased by the confounding action of pH regulatory mechanisms. Numerical simulation showed that MCT4, but not MCT1 or MCT2, endows cells with the capability of lactate extrusion in high lactate environments. The revised kinetic properties and novel transport assays may help in developing small-molecule MCT4 blockers for research and therapy.

physiology↗