Roles of pH in control of cell proliferation

A novel fluorescent sensor for evaluating pH changes in organophosphorus pesticides-treated cells and C. elegans

pH plays an important role in the evaluation of the healthy status in versatile circumstances. The fluctuation of pH could be affected by complex internal and external stimuli. Especially, the abnormal pH changes is a common characteristic of organophosphorus pesticides (OPs)-caused damage owing to the irreversible inhibition of acetylcholinesterase (AChE) activity. Therefore, the rapid and efficient detection of pH changes is of great significance for predicting the OPs poisoning in living system. However, quick and convenient detecting pH levels in living cells is still limited by the lack of effective chemical tools. Here, a novel fluorescent probe TH-1 based on ESIPT mechanism was synthesized, showing specific fluorescent effects in different pH solutions. Importantly, the AChE catalyzed the hydrolysis product of acetylthiocholine iodide (ATCh) and changed the pH of solution, which influence its fluorescent intensity. Moreover, the probe TH-1 was applied to detecting the pH levels in living cells and C. elegans, providing an efficient chemical sensor for revealing the potential mechanisms of OPs in physiological and pathological processes.

The Role of the Swollen State in Cell Proliferation

Cell swelling is known to be involved in various stages of the growth of plant cells and microorganisms but in mammalian cells how crucial a swollen state is for determining the fate of the cellular proliferation remains unclear. Recent evidence has increased our understanding of how the loss of the cell surface interactions with the extracellular matrix at early mitosis decreases the membrane tension triggering curvature changes in the plasma membrane and the activation of the sodium/hydrogen (Na +/H +) exchanger (NHE1) that drives osmotic swelling. Such a swollen state is temporary, but it is critical to alter essential membrane biophysical parameters that are required to activate Ca2 + channels and modulate the opening of K + channels involved in setting the membrane potential. A decreased membrane potential across the mitotic cell membrane enhances the clustering of Ras proteins involved in the Ca2 + and cytoskeleton-driven events that lead to cell rounding. Changes in the external mechanical and osmotic forces also have an impact on the lipid composition of the plasma membrane during mitosis.

Inflammatory response to bioceramic and epoxy resin-based endodontic sealers implanted in mice subcutaneous tissue: An in vivo study

To evaluate the inflammatory tissue response to BioRoot™ RCS (BR) and AH Plus Jet (AHPJ) sealers implanted in mice subcutaneous tissue. It was hypothesized that the inflammatory tissue response to BR would be milder than to AHPJ. An in vivo study was carried out using isogenic mice. The sealers were implanted during standardized surgical procedures. The inflammatory response was evaluated by microscopic analysis and von Kossa reaction in the reactionary tissue around the specimens after 7, 21, and 63 days. For comparisons, a zinc oxide and eugenol sealer (ZOE) was used as a positive control, in addition to a negative control without a sealer (n = 10 per group/period). All statistical analyses considered a significance level of 5%. All endodontic sealers triggered an inflammatory tissue response after 7 days. BR had a higher inflammatory cell count and a thicker fibrous capsule when compared with AHPJ, but both were less inflammatory than ZOE (p < .001). After 21 days, BR continued to trigger an intense inflammatory tissue response, higher in both microscopic parameters compared to AHPJ, and a thicker fibrous capsule than ZOE (p < .001). After 63 days, the inflammatory tissue response decreased in BR, matching the fibrous capsule thickness with AHPJ and ZOE. BR promoted intense calcium precipitation in all study periods. After 63 days, AHPJ and BR sealers were more biocompatible to subcutaneous mice tissue, but AHPJ present better early inflammatory response, as well as BR showed potential bioactivity. RESEARCH HIGHLIGHTS: The inflammatory tissue response triggered by a bioceramic endodontic sealer (BR) was not milder than that triggered by an epoxy-resin based endodontic sealer (AHPJ) during the first 3 weeks, considering the microscopic analysis of the reactionary tissue.

Regulation of cancer cell lipid metabolism and oxidative phosphorylation by microenvironmental acidosis

The expansion of cancer cell mass in solid tumors generates a harsh environment characterized by dynamically varying levels of acidosis, hypoxia, and nutrient deprivation. Because acidosis inhibits glycolytic metabolism and hypoxia inhibits oxidative phosphorylation, cancer cells that survive and grow in these environments must rewire their metabolism and develop a high degree of metabolic plasticity to meet their energetic and biosynthetic demands. Cancer cells frequently upregulate pathways enabling the uptake and utilization of lipids and other nutrients derived from dead or recruited stromal cells, and in particular lipid uptake is strongly enhanced in acidic microenvironments. The resulting lipid accumulation and increased reliance on β-oxidation and mitochondrial metabolism increase susceptibility to oxidative stress, lipotoxicity, and ferroptosis, in turn driving changes that may mitigate such risks. The spatially and temporally heterogeneous tumor microenvironment thus selects for invasive, metabolically flexible, and resilient cancer cells capable of exploiting their local conditions and of seeking out more favorable surroundings. This phenotype relies on the interplay between metabolism, acidosis, and oncogenic mutations, driving metabolic signaling pathways such as peroxisome proliferator-activated receptors (PPARs). Understanding the particular vulnerabilities of such cells may uncover novel therapeutic liabilities of the most aggressive cancer cells.

Na+/H+-exchange inhibition by cariporide is compensated via Na+,HCO3--cotransport and has no net growth consequences for ErbB2-driven breast carcinomas

Defense against intracellular acidification of breast cancer tissue depends on net acid extrusion via Na+,HCO3--cotransporter NBCn1/Slc4a7 and Na+/H+-exchanger NHE1/Slc9a1. NBCn1 is increasingly recognized as breast cancer susceptibility protein and promising therapeutic target, whereas evidence for targeting NHE1 is discordant. Currently, selective small molecule inhibitors exist against NHE1 but not NBCn1. Cellular assays-with some discrepancies-link NHE1 activity to proliferation, migration, and invasion; and disrupted NHE1 expression can reduce triple-negative breast cancer growth. Studies on human breast cancer tissue associate high NHE1 expression with reduced metastasis and-in some molecular subtypes-improved patient survival. Here, we evaluate Na+/H+-exchange and therapeutic potential of the NHE1 inhibitor cariporide/HOE-642 in murine ErbB2-driven breast cancer. Ex vivo, cariporide inhibits net acid extrusion in breast cancer tissue (IC50 = 0.18 μM) and causes small decreases in steady-state intracellular pH (pHi). In vivo, we deliver cariporide orally, by osmotic minipumps, and by intra- and peritumoral injections to address the low oral bioavailability and fast metabolism. Prolonged cariporide administration in vivo upregulates NBCn1 expression, shifts pHi regulation towards CO2/HCO3--dependent mechanisms, and shows no net effect on the growth rate of ErbB2-driven primary breast carcinomas. Cariporide also does not influence proliferation markers in breast cancer tissue. Oral, but not parenteral, cariporide elevates serum glucose by ∼1.5 mM. In conclusion, acute administration of cariporide ex vivo powerfully inhibits net acid extrusion from breast cancer tissue but lowers steady-state pHi minimally. Prolonged cariporide administration in vivo is compensated via NBCn1 and we observe no discernible effect on growth of ErbB2-driven breast carcinomas.

Active Magnesium Boride/Alginate Hydrogels Rejuvenate Senescent Cells

The clearance of senescent cells may be detrimental to low cell density diseases, such as intervertebral disc degeneration (IVDD), and rejuvenating these cells presents a formidable obstacle. In this study, we investigate a mild-alkalization strategy employing magnesium boride-alginate (MB-ALG) hydrogels to rejuvenate senescent cells associated with age-related diseases. MB-ALG hydrogels proficiently ensnare senescent cells owing to their surface roughness. The hydrolysis of MB-ALG hydrogels liberates hydroxide ions (OH-), effecting a transition from an acidic microenvironment (pH ∼ 6.2) to a mildly alkaline state (pH ∼ 8.0), thereby fostering senescent cell proliferation via activation of the PI3K/Akt/mTOR pathway. Additionally, H2 aids in ROS clearance, which reduces cellular oxidative stress. And, Mg2+ rejuvenates senescent cells by inhibiting Ca2+ influx and fine-tuning the sirt1-p53 signaling pathways. Both in vitro and in vivo experiments conducted on rat intervertebral discs corroborate the sustained antisenescence and rejuvenation properties of MB-ALG hydrogels, with effects persisting for up to 12 weeks postoperation. These discoveries elucidate the role of mild-alkalization in dictating cellular destiny and provide key insights for addressing age-related diseases.

pH-Responsive Aminobenzocoumarins as Fluorescent Probes for Biological Acidity

Regulation of pH plays an essential role in orchestrating the delicate cellular machinery responsible for life as we know it. Its abnormal values are indicative of aberrant cellular behavior and associated with pathologies including cancer progression or solid tumors. Here, we report a series of bent and linear aminobenzocoumarins decorated with different substituents. We investigate their photophysical properties and demonstrate that the probes display strong pH-responsive fluorescence "turn on" behavior in highly acidic environments, with enhancement up to 300-fold. In combination with their low cytotoxicity, this behavior enabled their application in bioimaging of acidic lysosomes in live human cells. We believe that these molecules serve as attractive lead structures for future rational design of novel biocompatible fluorescent pH probes.

Spatially resolved analysis of microenvironmental gradient impact on cancer cell phenotypes

Despite the physiological and pathophysiological significance of microenvironmental gradients, e.g., for diseases such as cancer, tools for generating such gradients and analyzing their impact are lacking. Here, we present an integrated microfluidic-based workflow that mimics extracellular pH gradients characteristic of solid tumors while enabling high-resolution live imaging of, e.g., cell motility and chemotaxis, and preserving the capacity to capture the spatial transcriptome. Our microfluidic device generates a pH gradient that can be rapidly controlled to mimic spatiotemporal microenvironmental changes over cancer cells embedded in a 3D matrix. The device can be reopened allowing immunofluorescence analysis of selected phenotypes, as well as the transfer of cells and matrix to a Visium slide for spatially resolved analysis of transcriptional changes across the pH gradient. This workflow is easily adaptable to other gradients and multiple cell types and can therefore prove invaluable for integrated analysis of roles of microenvironmental gradients in biology.

Antibodies toward Na+,HCO3--cotransporter NBCn1/SLC4A7 block net acid extrusion and cause pH-dependent growth inhibition and apoptosis in breast cancer

BACKGROUND

Na+,HCO3--cotransporter NBCn1/Slc4a7 accelerates murine breast carcinogenesis. Lack of specific pharmacological tools previously restricted therapeutic targeting of NBCn1 and identification of NBCn1-dependent functions in human breast cancer.

METHODS

We develop extracellularly-targeted anti-NBCn1 antibodies, screen for functional activity on cells, and evaluate (a) mechanisms of intracellular pH regulation in human primary breast carcinomas, (b) proliferation, cell death, and tumor growth consequences of NBCn1 in triple-negative breast cancer, and (c) association of NBCn1-mediated Na+,HCO3--cotransport with human breast cancer metastasis.

RESULTS

We identify high-affinity (KD ≈ 0.14 nM) anti-NBCn1 antibodies that block human NBCn1-mediated Na+,HCO3--cotransport in cells, without cross-reactivity towards human NBCe1 or murine NBCn1. These anti-NBCn1 antibodies abolish Na+,HCO3--cotransport activity in freshly isolated primary organoids from human breast carcinomas and lower net acid extrusion effectively in primary breast cancer tissue from patients with macrometastases in axillary lymph nodes. Inhibitory anti-NBCn1 antibodies decelerate tumor growth in vivo by ~50% in a patient-derived xenograft model of triple-negative breast cancer and pH-dependently reduce colony formation, cause G2/M-phase cell cycle accumulation, and increase apoptosis of metastatic triple-negative breast cancer cells in vitro.

CONCLUSIONS

Inhibitory anti-NBCn1 antibodies block net acid extrusion in human breast cancer tissue, particularly from patients with disseminated disease, and pH-dependently limit triple-negative breast cancer growth.

Strengthening the basics: acids and bases influence vascular structure and function, tissue perfusion, blood pressure, and human cardiovascular disease

Acids and their conjugate bases accumulate in or dissipate from the interstitial space when tissue perfusion does not match the metabolic demand. Extracellular acidosis dilates most arterial beds, but associated acid-base disturbances-e.g., intracellular acidification and decreases in HCO3- concentration-can also elicit pro-contractile influences that diminish vasodilation and even dominate in some vascular beds to cause vasoconstriction. The ensemble activities of the acid-base-sensitive reactions in vascular smooth muscle and endothelial cells optimize vascular resistance for blood pressure control and direct the perfusion towards active tissue. In this review, we describe the mechanisms of intracellular pH regulation in the vascular wall and discuss how vascular smooth muscle and endothelial cells sense acid-base disturbances. We further deliberate on the functional effects of local acid-base disturbances and their integrated cardiovascular consequences under physiological and pathophysiological conditions. Finally, we address how mutations and polymorphisms in the molecular machinery that regulates pH locally and senses acid-base disturbances in the vascular wall can result in cardiovascular disease. Based on the emerging molecular insight, we propose that targeting local pH-dependent effectors-rather than systemic acid-base disturbances-has therapeutic potential to interfere with the progression and reduce the severity of cardiovascular disease.

Acid-base transporters in the context of tumor heterogeneity

The copious metabolic acid production and -extrusion by cancer cells render poorly vascularized regions of solid tumors highly acidic. A growing list of proton - and bicarbonate transporters has been suggested to contribute to net acid extrusion from cancer cells, and/or been shown to be dysregulated and favor malignant development in various cancers. The great majority of these roles have been studied at the level of the cancer cells. However, recent advances in understanding of the cellular and physicochemical heterogeneity of solid tumors both enable and necessitate a reexamination of the regulation and roles of acid-base transporters in such malignancies. This review will briefly summarize the state-of-the-art, with a focus on the SLC9A and SLC4A families, for which most evidence is available. This is followed by a discussion of key concepts and open questions arising from recent insights and of the challenges that need to be tackled to address them. Finally, opportunities and challenges in therapeutic targeting of the acid-base transportome in cancers will be addressed.

Targeting MYC at the intersection between cancer metabolism and oncoimmunology

MYC activation is a known hallmark of cancer as it governs the gene targets involved in various facets of cancer progression. Of interest, MYC governs oncometabolism through the interactions with its partners and cofactors, as well as cancer immunity via its gene targets. Recent investigations have taken interest in characterizing these interactions through multi-Omic approaches, to better understand the vastness of the MYC network. Of the several gene targets of MYC involved in either oncometabolism or oncoimmunology, few of them overlap in function. Prominent interactions have been observed with MYC and HIF-1α, in promoting glucose and glutamine metabolism and activation of antigen presentation on regulatory T cells, and its subsequent metabolic reprogramming. This review explores existing knowledge of the role of MYC in oncometabolism and oncoimmunology. It also unravels how MYC governs transcription and influences cellular metabolism to facilitate the induction of pro- or anti-tumoral immunity. Moreover, considering the significant roles MYC holds in cancer development, the present study discusses effective direct or indirect therapeutic strategies to combat MYC-driven cancer progression.

Recent Development of Implantable Chemical Sensors Utilizing Flexible and Biodegradable Materials for Biomedical Applications

Implantable chemical sensors built with flexible and biodegradable materials exhibit immense potential for seamless integration with biological systems by matching the mechanical properties of soft tissues and eliminating device retraction procedures. Compared with conventional hospital-based blood tests, implantable chemical sensors have the capability to achieve real-time monitoring with high accuracy of important biomarkers such as metabolites, neurotransmitters, and proteins, offering valuable insights for clinical applications. These innovative sensors could provide essential information for preventive diagnosis and effective intervention. To date, despite extensive research on flexible and bioresorbable materials for implantable electronics, the development of chemical sensors has faced several challenges related to materials and device design, resulting in only a limited number of successful accomplishments. This review highlights recent advancements in implantable chemical sensors based on flexible and biodegradable materials, encompassing their sensing strategies, materials strategies, and geometric configurations. The following discussions focus on demonstrated detection of various objects including ions, small molecules, and a few examples of macromolecules using flexible and/or bioresorbable implantable chemical sensors. Finally, we will present current challenges and explore potential future directions.

Hexamethylene amiloride synergizes with venetoclax to induce lysosome-dependent cell death in acute myeloid leukemia

Tumors maintain an alkaline intracellular environment to enable rapid growth. The proton exporter NHE1 participates in maintenance of this pH gradient. However, whether targeting NHE1 could inhibit the growth of tumor cells remains unknown. Here, we report that the NHE1 inhibitor Hexamethylene amiloride (HA) efficiently suppresses the growth of AML cell lines. Moreover, HA combined with venetoclax synergized to efficiently inhibit the growth of AML cells. Interestingly, lysosomes are the main contributors to the synergism of HA and venetoclax in inhibiting AML cells. Most importantly, the combination of HA and venetoclax also had prominent anti-leukemia effects in both xenograft models and bone marrow samples from AML patients. In summary, our results provide evidence that the NHE1 inhibitor HA or its combination with venetoclax efficiently inhibits the growth of AML in vitro and in vivo.

Chronological development of functional fluorophores for bio-imaging

Functional fluorophores represent an emerging research field, distinguished by their diverse applications, especially in sensing and cellular imaging. After the discovery of quinine sulfate and subsequent elucidation of the fluorescence mechanism by Sir George Stokes, research in the field of fluorescence gained momentum. Over the past few decades, advancements in sophisticated instruments, including super-resolution microscopy, have further promoted cellular imaging using traditional fluorophores. These advancements include deciphering sensing mechanisms via photochemical reactions and scrutinizing the applications of fluorescent probes that specifically target organelles. This approach elucidates molecular interactions with biomolecules. Despite the abundance of literature illustrating different classes of probe development, a concise summary of newly developed fluorophores remains inadequate. In this review, we systematically summarize the chronological discovery of traditional fluorophores along with new fluorophores. We briefly discuss traditional fluorophores ranging from visible to near-infrared (NIR) in the context of cellular imaging and in vivo imaging. Furthermore, we explore ten new core fluorophores developed between 2007 and 2022, which exhibit advanced optical properties, providing new insights into bioimaging. We illustrate the utilization of new fluorophores in cellular imaging of biomolecules, such as reactive oxygen species (ROS), reactive nitrogen species (RNS), and proteins and microenvironments, especially pH and viscosity. Few of the fluorescent probes provided new insights into disease progression. Furthermore, we speculate on the potential prospects and significant challenges of existing fluorophores and their potential biomedical research applications. By addressing these aspects, we intend to illuminate the compelling advancements in fluorescent probe development and their potential influence across various fields.

How protons pave the way to aggressive cancers

Cancers undergo sequential changes to proton (H+) concentration and sensing that are consequences of the disease and facilitate its further progression. The impact of protonation state on protein activity can arise from alterations to amino acids or their titration. Indeed, many cancer-initiating mutations influence pH balance, regulation or sensing in a manner that enables growth and invasion outside normal constraints as part of oncogenic transformation. These cancer-supporting effects become more prominent when tumours develop an acidic microenvironment owing to metabolic reprogramming and disordered perfusion. The ensuing intracellular and extracellular pH disturbances affect multiple aspects of tumour biology, ranging from proliferation to immune surveillance, and can even facilitate further mutagenesis. As a selection pressure, extracellular acidosis accelerates disease progression by favouring acid-resistant cancer cells, which are typically associated with aggressive phenotypes. Although acid-base disturbances in tumours often occur alongside hypoxia and lactate accumulation, there is now ample evidence for a distinct role of H+-operated responses in key events underpinning cancer. The breadth of these actions presents therapeutic opportunities to change the trajectory of disease.

A pH-Sensitive Fluorescent Chemosensor Turn-On Based in a Salen Iron (III) Complex: Synthesis, Photophysical Properties, and Live-Cell Imaging Application

pH regulation is essential to allow normal cell function, and their imbalance is associated with different pathologic situations, including cancer. In this study, we present the synthesis of 2-(((2-aminoethyl)imino)methyl)phenol (HL1) and the iron (III) complex (Fe(L1)2Br, (C1)), confirmed by X-ray diffraction analysis. The absorption and emission properties of complex C1 were assessed in the presence and absence of different physiologically relevant analytes, finding a fluorescent turn-on when OH- was added. So, we determined the limit of detection (LOD = 3.97 × 10-9 M), stoichiometry (1:1), and association constant (Kas = 5.86 × 103 M-1). Using DFT calculations, we proposed a spontaneous decomposition mechanism for C1. After characterization, complex C1 was evaluated as an intracellular pH chemosensor on the human primary gastric adenocarcinoma (AGS) and non-tumoral gastric epithelia (GES-1) cell lines, finding fluorescent signal activation in the latter when compared to AGS cells due to the lower intracellular pH of AGS cells caused by the increased metabolic rate. However, when complex C1 was used on metastatic cancer cell lines (MKN-45 and MKN-74), a fluorescent turn-on was observed in both cell lines because the intracellular lactate amount increased. Our results could provide insights about the application of complex C1 as a metabolic probe to be used in cancer cell imaging.

Secretion of acetylated amino acids by drug-induced cancer cells: perspectives on metabolic-epigenetic alterations

The emerging understanding of the super-complex and heterogeneous nature of tumor is well supported by metabolic reprogramming, leading survival advantages. Metabolic reprogramming contributes to tumor responsiveness and resistance to various antitumor drugs. Among the numerous adaptations made by cancer cells in response to drug-induced perturbations, key metabolic alterations involving amino acids and acetylated derivatives of amino acids have received special attention. Considering these implications discussed, targeting cancer-associated metabolic pathways, particularly those involving acetylated amino acids, emerges as an important avenue in the pursuit of combinatorial anticancer strategies. As a result, the introduction of mimetic acetylated amino acids represents a promising new class of inhibitors that could be used alongside traditional chemotherapy agents.

Ratiometric fluorescent probes for pH mapping in cellular organelles

The intracellular pH (pHi) in organelles, including mitochondria, endoplasmic reticulum, lysosomes, and nuclei, differs from the cytoplasmic pH, and thus maintaining the pH of these organelles is crucial for cellular homeostasis. Alterations in the intracellular pH (ΔpHi) in organelles lead to the disruption of cell proliferation, ion transportation, cellular homeostasis, and even cell death. Hence, accurately mapping the pH of organelles is crucial. Accordingly, the development of fluorescence imaging probes for targeting specific organelles and monitoring their dynamics at the molecular level has become the forefront of research in the last three decades. Among them, ratiometric fluorescent probes minimize the interference from the excitation wavelength of light, auto-fluorescence from probe concentration, environmental fluctuations, and instrument sensitivity through self-correction compared to monochromatic fluorescent probes, which are known as turn-on/off fluorescent probes. Small-molecular ratiometric fluorescent probes for detecting ΔpHi are challenging yet demanding. To date, sixty-two ratiometric pH probes have been reported for monitoring internal pH alterations in cellular organelles. However, a critical review on organelle-specific ratiometric probes for pH mapping is still lacking. Thus, in the present review, we report the most recent advances in ratiometric pH probes and the previous data on the role of mapping the ΔpHi of cellular organelles. The development strategy, including ratiometric fluorescence with one reference signal (RFRS) and ratiometric fluorescence with two reversible signals (RFRvS), is systematically illustrated. Finally, we emphasize the major challenges in developing ratiometric probes that merit further research in the future.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

Chronic acidosis rewires cancer cell metabolism through PPARα signaling

The mechanisms linking tumor microenvironment acidosis to disease progression are not understood. Here, we used mammary, pancreatic, and colon cancer cells to show that adaptation to growth at an extracellular pH (pHe ) mimicking acidic tumor niches is associated with upregulated net acid extrusion capacity and elevated intracellular pH at physiological pHe , but not at acidic pHe . Using metabolic profiling, shotgun lipidomics, imaging and biochemical analyses, we show that the acid adaptation-induced phenotype is characterized by a shift toward oxidative metabolism, increased lipid droplet-, triacylglycerol-, peroxisome content and mitochondrial hyperfusion. Peroxisome proliferator-activated receptor-α (PPARA, PPARα) expression and activity are upregulated, at least in part by increased fatty acid uptake. PPARα upregulates genes driving increased mitochondrial and peroxisomal mass and β-oxidation capacity, including mitochondrial lipid import proteins CPT1A, CPT2 and SLC25A20, electron transport chain components, peroxisomal proteins PEX11A and ACOX1, and thioredoxin-interacting protein (TXNIP), a negative regulator of glycolysis. This endows acid-adapted cancer cells with increased capacity for utilizing fatty acids for metabolic needs, while limiting glycolysis. As a consequence, the acid-adapted cells exhibit increased sensitivity to PPARα inhibition. We conclude that PPARα is a key upstream regulator of metabolic changes favoring cancer cell survival in acidic tumor niches.

Crosstalk between tumor acidosis, p53 and extracellular matrix regulates pancreatic cancer aggressiveness

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive malignancy with minimal treatment options and a global rise in prevalence. PDAC is characterized by frequent driver mutations including KRAS and TP53 (p53), and a dense, acidic tumor microenvironment (TME). The relation between genotype and TME in PDAC development is unknown. Strikingly, when wild type (WT) Panc02 PDAC cells were adapted to growth in an acidic TME and returned to normal pH to mimic invasive cells escaping acidic regions, they displayed a strong increase of aggressive traits such as increased growth in 3-dimensional (3D) culture, adhesion-independent colony formation and invasive outgrowth. This pattern of acidosis-induced aggressiveness was observed in 3D spheroid culture as well as upon organotypic growth in matrigel, collagen-I and combination thereof, mimicking early and later stages of PDAC development. Acid-adaptation-induced gain of cancerous traits was further increased by p53 knockout (KO), but only in specific extracellular matrix (ECM) compositions. Akt- and Transforming growth factor-β (TGFβ) signaling, as well as expression of the Na⁺ /H⁺ exchanger NHE1, were increased by acid adaptation. Whereas Akt inhibition decreased spheroid growth regardless of treatment and genotype, stimulation with TGFβI increased growth of WT control spheroids, and inhibition of TGFβ signaling tended to limit growth under acidic conditions only. Our results indicate that a complex crosstalk between tumor acidosis, ECM composition and genotype contributes to PDAC development. The findings may guide future strategies for acidosis-targeted therapies.

Ion Channels in Gliomas-From Molecular Basis to Treatment

Ion channels provide the basis for the nervous system's intrinsic electrical activity. Neuronal excitability is a characteristic property of neurons and is critical for all functions of the nervous system. Glia cells fulfill essential supportive roles, but unlike neurons, they also retain the ability to divide. This can lead to uncontrolled growth and the formation of gliomas. Ion channels are involved in the unique biology of gliomas pertaining to peritumoral pathology and seizures, diffuse invasion, and treatment resistance. The emerging picture shows ion channels in the brain at the crossroads of neurophysiology and fundamental pathophysiological processes of specific cancer behaviors as reflected by uncontrolled proliferation, infiltration, resistance to apoptosis, metabolism, and angiogenesis. Ion channels are highly druggable, making them an enticing therapeutic target. Targeting ion channels in difficult-to-treat brain tumors such as gliomas requires an understanding of their extremely heterogenous tumor microenvironment and highly diverse molecular profiles, both representing major causes of recurrence and treatment resistance. In this review, we survey the current knowledge on ion channels with oncogenic behavior within the heterogeneous group of gliomas, review ion channel gene expression as genomic biomarkers for glioma prognosis and provide an update on therapeutic perspectives for repurposed and novel ion channel inhibitors and electrotherapy.

A role of salt bridges in mediating drug potency: A lesson from the N-myristoyltransferase inhibitors

The salt bridge is the strongest non-covalent interaction in nature and is known to participate in protein folding, protein-protein interactions, and molecular recognition. However, the role of salt bridges in the context of drug design has remained not well understood. Here, we report that a common feature in the mechanism of inhibition of the N-myristoyltransferases (NMT), promising targets for the treatment of protozoan infections and cancer, is the formation of a salt bridge between a positively charged chemical group of the small molecule and the negatively charged C-terminus of the enzyme. Substituting the inhibitor positively charged amine group with a neutral methylene group prevents the formation of the salt bridge and leads to a dramatic activity loss. Molecular dynamics simulations have revealed that salt bridges stabilize the NMT-ligand complexes by functioning as molecular clips that stabilize the conformation of the protein structure. As such, the creation of salt bridges between the ligands and their protein targets may find an application as a valuable tool in rational drug design.

Pectin-based bioinks for 3D models of neural tissue produced by a pH-controlled kinetics

Introduction: In the view of 3D-bioprinting with cell models representative of neural cells, we produced inks to mimic the basic viscoelastic properties of brain tissue. Moving from the concept that rheology provides useful information to predict ink printability, this study improves and expands the potential of the previously published 3D-reactive printing approach by introducing pH as a key parameter to be controlled, together with printing time. Methods: The viscoelastic properties, printability, and microstructure of pectin gels crosslinked with CaCO3 were investigated and their composition was optimized (i.e., by including cell culture medium, HEPES buffer, and collagen). Different cell models representative of the major brain cell populations (i.e., neurons, astrocytes, microglial cells, and oligodendrocytes) were considered. Results and Discussion: The outcomes of this study propose a highly controllable method to optimize the printability of internally crosslinked polysaccharides, without the need for additives or post-printing treatments. By introducing pH as a further parameter to be controlled, it is possible to have multiple (pH-dependent) crosslinking kinetics, without varying hydrogel composition. In addition, the results indicate that not only cells survive and proliferate following 3D-bioprinting, but they can also interact and reorganize hydrogel microstructure. Taken together, the results suggest that pectin-based hydrogels could be successfully applied for neural cell culture.

Hypoxia-Inducible Factor-1: A Novel Therapeutic Target for the Management of Cancer, Drug Resistance, and Cancer-Related Pain

Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor that regulates the transcription of many genes that are responsible for the adaptation and survival of tumor cells in hypoxic environments. Over the past few decades, tremendous efforts have been made to comprehensively understand the role of HIF-1 in tumor progression. Based on the pivotal roles of HIF-1 in tumor biology, many HIF-1 inhibitors interrupting expression, stabilization, DNA binding properties, or transcriptional activity have been identified as potential therapeutic agents for various cancers, yet none of these inhibitors have yet been successfully translated into clinically available cancer treatments. In this review, we briefly introduce the regulation of the HIF-1 pathway and summarize its roles in tumor cell proliferation, angiogenesis, and metastasis. In addition, we explore the implications of HIF-1 in the development of drug resistance and cancer-related pain: the most commonly encountered obstacles during conventional anticancer therapies. Finally, the current status of HIF-1 inhibitors in clinical trials and their perspectives are highlighted, along with their modes of action. This review provides new insights into novel anticancer drug development targeting HIF-1. HIF-1 inhibitors may be promising combinational therapeutic interventions to improve the efficacy of current cancer treatments and reduce drug resistance and cancer-related pain.

Effects of Neutralization on the Physicochemical, Mechanical, and Biological Properties of Ammonium-Hydroxide-Crosslinked Chitosan Scaffolds

It has been reported that chitosan scaffolds, due to their physicochemical properties, stimulate cell proliferation in different tissues of the human body. This study aimed to determine the physicochemical, mechanical, and biological properties of chitosan scaffolds crosslinked with ammonium hydroxide, with different pH values, to better understand cell behavior depending on the pH of the biomaterial. Scaffolds were either neutralized with sodium hydroxide solution, washed with distilled water until reaching a neutral pH, or kept at alkaline pH. Physicochemical characterization included scanning electron microscopy (SEM), elemental composition (EDX), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), and mechanical testing. In vitro cytotoxicity was assessed via dental-pulp stem cells' (DPSCs') biocompatibility. The results revealed that the neutralized scaffolds exhibited better cell proliferation and morphology. It was concluded that the chitosan scaffolds' high pH (due to residual ammonium hydroxide) decreases DPSCs' cell viability.

Preparation and Characterization of Porous Poly(Lactic Acid)/Poly(Butylene Adipate-Co-Terephthalate) (PLA/PBAT) Scaffold with Polydopamine-Assisted Biomineralization for Bone Regeneration

The development of scaffolds that simultaneously provide porous architectures and osteogenic properties is the major challenge in tissue engineering. Herein, a scaffold with high porosity and well interconnected networks, namely poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT), was fabricated using the gas foaming/ammonium bicarbonate particulate leaching technique. Mussel-inspired polydopamine (PDA)-assisted biomineralization generated by two-step simple soaking in dopamine solution and 10× SBF-like solution was performed to improve the material's osteogenicity. Highly porous scaffolds available in less organized opened cell structures with diameters ranging from 10 µm to 100 µm and 200 µm to 500 µm were successfully prepared. The well interconnected porous architectures were observed through the whole thickness of the scaffold. The even deposition of the organic-inorganic bioactive mineralized layer composed of PDA and nano-scale hydroxyapatite (HA) crystals on the scaffold surface was evidenced by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The developed scaffold exhibited high total porosity (84.17 ± 1.29%), a lower surface contact angle (θ = 45.7 ± 5.9°), lower material degradation rate (7.63 ± 2.56%), and a high level of material biocompatibility. The MTT assay and Alizarin Red S staining (ARS) confirmed its osteogenic enhancement property toward human osteoblast-like cells (MG-63). These results clarified that the developed porous PLA/PBAT scaffold with PDA-assisted biomineralization exhibited good potential for application as a biomaterial for bone tissue regeneration and hard tissue engineering.

Melatonin Treatment Triggers Metabolic and Intracellular pH Imbalance in Glioblastoma

Metabolic rewiring in glioblastoma (GBM) is linked to intra- and extracellular pH regulation. In this study, we sought to characterize the role of melatonin on intracellular pH modulation and metabolic consequences to identify the mechanisms of action underlying melatonin oncostatic effects on GBM tumor initiating cells. GBM tumor initiating cells were treated at different times with melatonin (1.5 and 3.0 mM). We analyzed melatonin’s functional effects on GBM proliferation, cell cycle, viability, stemness, and chemo-radiosensitivity. We then assessed the effects of melatonin on GBM metabolism by analyzing the mitochondrial and glycolytic parameters. We also measured the intracellular and extracellular pH. Finally, we tested the effects of melatonin on a mouse subcutaneous xenograft model. We found that melatonin downregulated LDHA and MCT4, decreasing lactate production and inducing a decrease in intracellular pH that was associated with an increase in ROS and ATP depletion. These changes blocked cell cycle progression and induced cellular death and we observed similar results in vivo. Melatonin’s cytotoxic effects on GBM were due, at least in part, to intracellular pH modulation, which has emerged as a newly identified mechanism, providing new insights into the oncostatic effect of melatonin on GBM.

Design of foldable, responsively drug-eluting polyacrylic intraocular lens bulk materials for prevention of postoperative complications

Posterior capsular opacification (PCO), resulting from undesired intracapsular cell proliferation, is the most common complication of intraocular lens (IOL) implantation after cataract surgery. In recent years, IOLs have been developed into a drug delivery platform. Compared with traditional eye drops, drug-loaded IOLs have the characteristics of independent patient compliance and no other operation except surgical implantation. In this work, a series of poly(glycidyl methacrylate-co-2-(2-ethoxyethoxy)ethyl acrylate) (PGE) acrylic intraocular lens materials were synthesized as drug delivery platforms. The PGE synthesized with 10% crosslinking agent has excellent optical, foldable, and thermomechanical properties. An aldehyde group was subsequently introduced into the PGE chains, and an antiproliferative drug (doxorubicin) was immobilized onto the PGE chains via an H⁺-sensitive imine bond. The IOL exhibits H⁺-dependent Dox release behavior in a simulated pathological environment. The in vitro and in vivo systematical evaluations indicate that such a responsively drug-eluting PGE IOL can effectively prevent PCO.

Acid Adaptation Promotes TRPC1 Plasma Membrane Localization Leading to Pancreatic Ductal Adenocarcinoma Cell Proliferation and Migration through Ca2+ Entry and Interaction with PI3K/CaM

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers globally, with a 5-year overall survival of less than 10%. The development and progression of PDAC are linked to its fluctuating acidic tumor microenvironment. Ion channels act as important sensors of this acidic tumor microenvironment. They transduce extracellular signals and regulate signaling pathways involved in all hallmarks of cancer. In this study, we evaluated the interplay between a pH-sensitive ion channel, the calcium (Ca²⁺) channel transient receptor potential C1 (TRPC1), and three different stages of the tumor microenvironment, normal pH, acid adaptation, and acid recovery, and its impact on PDAC cell migration, proliferation, and cell cycle progression. In acid adaptation and recovery conditions, TRPC1 localizes to the plasma membrane, where it interacts with PI3K and calmodulin, and permits Ca²⁺ entry, which results in downstream signaling, leading to proliferation and migration. Thus, TRPC1 exerts a more aggressive role after adaptation to the acidic tumor microenvironment.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies, with a low overall survival rate of less than 10% and limited therapeutic options. Fluctuations in tumor microenvironment pH are a hallmark of PDAC development and progression. Many ion channels are bona fide cellular sensors of changes in pH. Yet, the interplay between the acidic tumor microenvironment and ion channel regulation in PDAC is poorly understood. In this study, we show that acid adaption increases PANC-1 cell migration but attenuates proliferation and spheroid growth, which are restored upon recovery. Moreover, acid adaptation and recovery conditions favor the plasma membrane localization of the pH-sensitive calcium (Ca²⁺) channel transient receptor potential C1 (TRPC1), TRPC1-mediated Ca²⁺ influx, channel interaction with the PI3K p85α subunit and calmodulin (CaM), and AKT and ERK1/2 activation. Knockdown (KD) of TRPC1 suppresses cell migration, proliferation, and spheroid growth, notably in acid-recovered cells. KD of TRPC1 causes the accumulation of cells in G0/G1 and G2/M phases, along with reduced expression of CDK6, −2, and −1, and cyclin A, and increased expression of p21^CIP1. TRPC1 silencing decreases the basal Ca²⁺ influx in acid-adapted and -recovered cells, but not in normal pH conditions, and Ca²⁺ chelation reduces cell migration and proliferation solely in acid adaptation and recovery conditions. In conclusion, acid adaptation and recovery reinforce the involvement of TRPC1 in migration, proliferation, and cell cycle progression by permitting Ca²⁺ entry and forming a complex with the PI3K p85α subunit and CaM.

Microenvironment in Oral Potentially Malignant Disorders: Multi-Dimensional Characteristics and Mechanisms of Carcinogenesis

Oral potentially malignant disorders (OPMDs) are a group of diseases involving the oral mucosa and that have a risk of carcinogenesis. The microenvironment is closely related to carcinogenesis and cancer progression by regulating the immune response, cell metabolic activities, and mechanical characteristics. Meanwhile, there are extensive interactions between the microenvironments that remodel and provide favorable conditions for cancer initiation. However, the changes, exact roles, and interactions of microenvironments during the carcinogenesis of OPMDs have not been fully elucidated. Here, we present an updated landscape of the microenvironments in OPMDs, emphasizing the changes in the immune microenvironment, metabolic microenvironment, mechanical microenvironment, and neural microenvironment during carcinogenesis and their carcinogenic mechanisms. We then propose an immuno–metabolic–mechanical–neural interaction network to describe their close relationships. Lastly, we summarize the therapeutic strategies for targeting microenvironments, and provide an outlook on future research directions and clinical applications. This review depicts a vivid microenvironment landscape and sheds light on new strategies to prevent the carcinogenesis of OPMDs.

Ca2+ Signalling and Hypoxia/Acidic Tumour Microenvironment Interplay in Tumour Progression

Solid tumours are characterised by an altered microenvironment (TME) from the physicochemical point of view, displaying a highly hypoxic and acidic interstitial fluid. Hypoxia results from uncontrolled proliferation, aberrant vascularization and altered cancer cell metabolism. Tumour cellular apparatus adapts to hypoxia by altering its metabolism and behaviour, increasing its migratory and metastatic abilities by the acquisition of a mesenchymal phenotype and selection of aggressive tumour cell clones. Extracellular acidosis is considered a cancer hallmark, acting as a driver of cancer aggressiveness by promoting tumour metastasis and chemoresistance via the selection of more aggressive cell phenotypes, although the underlying mechanism is still not clear. In this context, Ca2+ channels represent good target candidates due to their ability to integrate signals from the TME. Ca2+ channels are pH and hypoxia sensors and alterations in Ca2+ homeostasis in cancer progression and vascularization have been extensively reported. In the present review, we present an up-to-date and critical view on Ca2+ permeable ion channels, with a major focus on TRPs, SOCs and PIEZO channels, which are modulated by tumour hypoxia and acidosis, as well as the consequent role of the altered Ca2+ signals on cancer progression hallmarks. We believe that a deeper comprehension of the Ca2+ signalling and acidic pH/hypoxia interplay will break new ground for the discovery of alternative and attractive therapeutic targets.

WPI Hydrogels with a Prolonged Drug-Release Profile for Antimicrobial Therapy

Infectious sequelae caused by surgery are a significant problem in modern medicine due to their reduction of therapeutic effectiveness and the patients’ quality of life.Recently, new methods of local antimicrobial prophylaxis of postoperative sequelae have been actively developed. They allow high local concentrations of drugs to be achieved, increasing the antibiotic therapy’s effectiveness while reducing its side effects. We have developed and characterized antimicrobial hydrogels based on an inexpensive and biocompatible natural substance from the dairy industry—whey protein isolate—as matrices for drug delivery. The release of cefazolin from the pores of hydrogel structures directly depends on the amount of the loaded drug and occurs in a prolonged manner for three days. Simultaneously with the antibiotic release, hydrogel swelling and partial degradation occurs. The WPI hydrogels absorb solvent, doubling in size in three days and retaining cefazolin throughout the duration of the experiment. The antimicrobial activity of cefazolin-loaded WPI hydrogels against Staphylococcus aureus growth is prolonged in comparison to that of the free cefazolin. The overall cytotoxic effect of cefazolin-containing WPI hydrogels is lower than that of free antibiotics. Thus, our work shows that antimicrobial WPI hydrogels are suitable candidates for local antibiotic therapy of infectious surgical sequelae.

Sensing Hypochlorite or pH variations in live cells and zebrafish with a novel dual-functional ratiometric and colorimetric chemosensor

Both HClO and pH are essential players in multiple biological processes, which thus need to be controlled properly. Dysregulated HClO or pH correlates with many diseases. To meet these challenges, we need to develop highly competent probes for monitoring them. Over the years, despite a rich history of the development of HClO or pH probes, those that can do both jobs are still deficient. Herein, we present a novel dual-functional chemosensor, CMHN, which exhibits a blue and red shift of its fluorescence emission upon reacting with HClO or OH^-, respectively. CMHN was successfully harnessed in the imaging detection of HClO or OH^- in aqueous solutions, live cells, and zebrafish. Results indicated CMHN can detect HClO with high sensitivity (LOD -132 nM), a quick response time (<70 s), and high selectivity over dozens of interfering species through a colorimetric and ratiometric response. Besides, CMHN can probe pH changes sensitively and reversibly. Its working mechanism was verified by DFT calculations. These superior features make CMHN excel among the HClO or pH probes reported so far. Taken together, CMHN replenishes the deficiency in currently developed HClO or pH probes and paves the way for developing multifunctional HClO or pH probes in the future.

The acidic tumour microenvironment: Manipulating the immune response to elicit escape

The success of cancer treatment relies on the composition of the tumour microenvironment which is comprised of tumour cells, blood vessels, stromal cells, immune cells, and extracellular matrix components. Barriers to effective cancer treatment need to be overcome, and the acidic microenvironment of the tumour provides a key target for treatment. This review intends to provide an overview of the effects that low extracellular pH has on components of the tumour microenvironment and how they contribute to immune escape. Further, potential therapeutic targets will be discussed.

Dual roles of AMAP1 in the transcriptional regulation and intracellular trafficking of carbonic anhydrase IX

BACKGROUND

The cell-surface enzyme carbonic anhydrase IX (CAIX/CA9) promotes tumor growth, survival, invasion, and metastasis, mainly via its pH-regulating functions. Owing to its tumor-specific expression, CAIX-targeting antibodies/chemicals are utilized for therapeutic and diagnostic purposes. However, mechanisms of CAIX trafficking, which affects such CAIX-targeting modalities remain unclear. In this study, roles of the AMAP1-PRKD2 pathway, which mediates integrin recycling of invasive cancer cells, in CAIX trafficking were investigated.

METHODS

Using highly invasive MDA-MB-231 breast cancer cells, the physical association and colocalization of endogenous proteins were analyzed by immunoprecipitation and immunofluorescence, protein/mRNA levels were quantified by western blotting/qPCR, and cell-surface transport and intracellular/extracellular pH regulation were measured by biotin-labeling and fluorescent dye-based assays, respectively. The correlation between mRNA levels and patients' prognoses was analyzed using a TCGA breast cancer dataset.

RESULTS

AMAP1 associated with the CAIX protein complex, and they colocalized at the plasma membrane and tubulovesicular structures. AMAP1 knockdown reduced total/surface CAIX, induced its lysosomal accumulation and degradation, and affected intracellular/extracellular pH. PRKD2 knockdown excluded AMAP1 from the CAIX complex and reduced total CAIX in a lysosome-dependent manner. Unexpectedly, AMAP1 knockdown also reduced CAIX mRNA. AMAP1 interacted with PIAS3, which stabilizes HIF-1α, a transcriptional regulator of CA9. AMAP1 knockdown inhibited the PIAS3-HIF-1α interaction and destabilized the HIF-1α protein. High-ASAP1 (AMAP1-encoding gene) together with high-PIAS3 correlated with high-CA9 and an unfavorable prognosis in breast cancer.

CONCLUSION

The AMAP1-PRKD2 pathway regulates CAIX trafficking, and modulates its total/surface expression. The AMAP1-PIAS3 interaction augments CA9 transcription by stabilizing HIF-1α, presumably contributing to an unfavorable prognosis.

An Optogenetic Tool to Raise Intracellular pH in Single Cells and Drive Localized Membrane Dynamics

Intracellular pH (pHi) dynamics are critical for regulating normal cell physiology. For example, transient increases in pHi (7.2–7.6) regulate cell behaviors like cell polarization, actin cytoskeleton remodeling, and cell migration. Most studies on pH-dependent cell behaviors have been performed at the population level and use nonspecific methods to manipulate pHi. The lack of tools to specifically manipulate pHi at the single-cell level has hindered investigation of the role of pHi dynamics in driving single cell behaviors. In this work, we show that Archaerhodopsin (ArchT), a light-driven outward proton pump, can be used to elicit robust and physiological pHi increases over the minutes time scale. We show that activation of ArchT is repeatable, enabling the maintenance of high pHi in single cells for up to 45 minutes. We apply this spatiotemporal pHi manipulation tool to determine whether increased pHi is a sufficient driver of membrane ruffling in single cells. Using the ArchT tool, we show that increased pHi in single cells can drive localized membrane ruffling responses within seconds and increased membrane dynamics (both protrusion and retraction events) compared to unstimulated ArchT cells as well as control cells. Overall, this tool allows us to directly investigate the relationship between increased pHi and single cell behaviors such as membrane ruffling. This tool will be transformative in facilitating experiments that are required to determine roles for increased pHi in driving single cell behaviors.

Expression and function of SLC38A5, an amino acid-coupled Na+/H+ exchanger, in triple-negative breast cancer and its relevance to macropinocytosis

Metabolic reprogramming in cancer necessitates increased amino acid uptake, which is accomplished by up-regulation of specific amino acid transporters. However, not all tumors rely on any single amino acid transporter for this purpose. Here, we report on the differential up-regulation of the amino acid transporter SLC38A5 in triple-negative breast cancer (TNBC). The up-regulation is evident in TNBC tumors, conventional and patient-derived xenograft TNBC cell lines, and a mouse model of spontaneous TNBC mammary tumor. The up-regulation is confirmed by functional assays. SLC38A5 is an amino acid-dependent Na+/H+ exchanger which transports Na+ and amino acids into cells coupled with H+ efflux. Since cell-surface Na+/H+ exchanger is an established inducer of macropinocytosis, an endocytic process for cellular uptake of bulk fluid and its components, we examined the impact of SLC38A5 on macropinocytosis in TNBC cells. We found that the transport function of SLC38A5 is coupled to the induction of macropinocytosis. Surprisingly, the transport function of SLC38A5 is inhibited by amilorides, the well-known inhibitors of Na+/H+ exchanger. Down-regulation of SLC38A5 in TNBC cells attenuates serine-induced macropinocytosis and reduces cell proliferation significantly as assessed by multiple methods, but does not induce cell death. The Cancer Genome Atlas database corroborates SLC38A5 up-regulation in TNBC. This represents the first report on the selective expression of SLC38A5 in TNBC and its role as an inducer of macropinocytosis, thus revealing a novel, hitherto unsuspected, function for an amino acid transporter that goes beyond amino acid delivery but is still relevant to cancer cell nutrition and proliferation.

Beyond dueling: roles of the type VI secretion system in microbiome modulation, pathogenesis and stress resistance

Bacteria inhabit diverse and dynamic environments, where nutrients may be limited and toxic chemicals can be prevalent. To adapt to these stressful conditions, bacteria have evolved specialized protein secretion systems, such as the type VI secretion system (T6SS) to facilitate their survival. As a molecular syringe, the T6SS expels various effectors into neighboring bacterial cells, eukaryotic cells, or the extracellular environment. These effectors improve the competitive fitness and environmental adaption of bacterial cells. Although primarily recognized as antibacterial weapons, recent studies have demonstrated that T6SSs have functions beyond interspecies competition. Here, we summarize recent research on the role of T6SSs in microbiome modulation, pathogenesis, and stress resistance.

Shikonin suppresses the epithelial-to-mesenchymal transition by downregulating NHE1 in bladder cancer cells

Shikonin (SK) is the major bioactive component extracted from the roots of Lithospermum erythrorhizon with anticancer activity. SK could inhibit the epithelial-to-mesenchymal transition (EMT) of cancer cells. However, the underlying mechanism is elusive. In the present study, the inhibitory activities of SK on proliferation, invasion and migration were examined in bladder cancer (BC) cells. SK potently decreased the viabilities of BC cells but showed less cytotoxicity to normal bladder epithelial cells. Moreover, SK reversed the EMT, suppressed the migration and invasion of BC cells. Intriguingly, NHE1, the major proton efflux pump, was dramatically down-regulated by SK. The EMT-inhibitory effect of SK was mediated by NHE1 down-regulation, as NHE1-overexpress alleviated while Cariporide (NHE1 inhibitor) enhanced this effect. Further, enforced alkalinization of intracellular pH (pHi) reversed the EMT-inhibitory effect of SK, indicating a key role of acidic pHi in this process. Finally, elevated NHE1 expression was observed in human bladder cancer tissues. Collectively, this research reveals a supportive effect of NHE1 and alkaline pHi on EMT. SK can suppress EMT through inhibiting NHE1 and hence inducing an acidic pHi.

Endothelial metabolism in pulmonary vascular homeostasis and acute respiratory distress syndrome

Capillary endothelial cells possess a specialized metabolism necessary to adapt to the unique alveolar-capillary environment. Here, we highlight how endothelial metabolism preserves the integrity of the pulmonary circulation by controlling vascular permeability, defending against oxidative stress, facilitating rapid migration and angiogenesis in response to injury, and regulating the epigenetic landscape of endothelial cells. Recent reports on single-cell RNA-sequencing reveal subpopulations of pulmonary capillary endothelial cells with distinctive reparative capacities, which potentially offer new insight into their metabolic signature. Lastly, we discuss broad implications of pulmonary vascular metabolism on acute respiratory distress syndrome, touching on emerging findings of endotheliitis in coronavirus disease 2019 (COVID-19) lungs.

Ion Channels, Transporters, and Sensors Interact with the Acidic Tumor Microenvironment to Modify Cancer Progression

Solid tumors, including breast carcinomas, are heterogeneous but typically characterized by elevated cellular turnover and metabolism, diffusion limitations based on the complex tumor architecture, and abnormal intra- and extracellular ion compositions particularly as regards acid-base equivalents. Carcinogenesis-related alterations in expression and function of ion channels and transporters, cellular energy levels, and organellar H⁺ sequestration further modify the acid-base composition within tumors and influence cancer cell functions, including cell proliferation, migration, and survival. Cancer cells defend their cytosolic pH and HCO₃^- concentrations better than normal cells when challenged with the marked deviations in extracellular H⁺, HCO₃^-, and lactate concentrations typical of the tumor microenvironment. Ionic gradients determine the driving forces for ion transporters and channels and influence the membrane potential. Cancer and stromal cells also sense abnormal ion concentrations via intra- and extracellular receptors that modify cancer progression and prognosis. With emphasis on breast cancer, the current review first addresses the altered ion composition and the changes in expression and functional activity of ion channels and transporters in solid cancer tissue. It then discusses how ion channels, transporters, and cellular sensors under influence of the acidic tumor microenvironment shape cancer development and progression and affect the potential of cancer therapies.

Acid-base transporters and pH dynamics in human breast carcinomas predict proliferative activity, metastasis, and survival

Breast cancer heterogeneity in histology and molecular subtype influences metabolic and proliferative activity and hence the acid load on cancer cells. We hypothesized that acid-base transporters and intracellular pH (pH_i) dynamics contribute inter-individual variability in breast cancer aggressiveness and prognosis. We show that Na⁺,HCO₃^- cotransport and Na⁺/H⁺ exchange dominate cellular net acid extrusion in human breast carcinomas. Na⁺/H⁺ exchange elevates pH_i preferentially in estrogen receptor-negative breast carcinomas, whereas Na⁺,HCO₃^- cotransport raises pH_i more in invasive lobular than ductal breast carcinomas and in higher malignancy grade breast cancer. HER2-positive breast carcinomas have elevated protein expression of Na⁺/H⁺ exchanger NHE1/SLC9A1 and Na⁺,HCO₃^- cotransporter NBCn1/SLC4A7. Increased dependency on Na⁺,HCO₃^- cotransport associates with severe breast cancer: enlarged CO₂/HCO₃^--dependent rises in pH_i predict accelerated cell proliferation, whereas enhanced CO₂/HCO₃^--dependent net acid extrusion, elevated NBCn1 protein expression, and reduced NHE1 protein expression predict lymph node metastasis. Accordingly, we observe reduced survival for patients suffering from luminal A or basal-like/triple-negative breast cancer with high SLC4A7 and/or low SLC9A1 mRNA expression. We conclude that the molecular mechanisms of acid-base regulation depend on clinicopathological characteristics of breast cancer patients. NBCn1 expression and dependency on Na⁺,HCO₃^- cotransport for pH_i regulation, measured in biopsies of human primary breast carcinomas, independently predict proliferative activity, lymph node metastasis, and patient survival.

Interplay between H1N1 influenza a virus infection, extracellular and intracellular respiratory tract pH, and host responses in a mouse model

During influenza A virus (IAV) entry, the hemagglutinin (HA) protein is triggered by endosomal low pH to undergo irreversible structural changes that mediate membrane fusion. HA proteins from different isolates vary in the pH at which they become activated in endosomes or become irreversible inactivated if exposed to extracellular acid. Little is known about extracellular pH in the upper respiratory tracts of mammals, how pH may shift during IAV infection, and its impact on replication of viruses that vary in HA activation pH. Here, we inoculated DBA/2J mice intranasally with A/TN/1-560/2009 (H1N1) (activation pH 5.5) or a mutant containing the destabilizing mutation HA1-Y17H (pH 6.0). We measured the kinetics of extracellular pH during infection using an optical pH-sensitive microsensor probe placed in the naris, nasal sinus, soft palate, and trachea. We also measured intracellular pH of single-cell suspensions of live, primary lung epithelial cells with various wavelength pH-sensitive dyes localized to cell membranes, cytosol, endosomes, secretory vesicles, microtubules, and lysosomes. Infection with either virus decreased extracellular pH and increased intracellular pH. Peak host immune responses were observed at 2 days post infection (DPI) and peak pH changes at 5 DPI. Extracellular and intracellular pH returned to baseline by 7 DPI in mice infected with HA1-Y17H and was restored later in wildtype-infected. Overall, IAV infection altered respiratory tract pH, which in turn modulated replication efficiency. This suggests a virus-host pH feedback loop that may select for IAV strains containing HA proteins of optimal pH stability, which may be approximately pH 5.5 in mice but may differ in other species.

SLC6A14 and SLC38A5 Drive the Glutaminolysis and Serine-Glycine-One-Carbon Pathways in Cancer

The glutaminolysis and serine–glycine–one-carbon pathways represent metabolic reactions that are reprogramed and upregulated in cancer; these pathways are involved in supporting the growth and proliferation of cancer cells. Glutaminolysis participates in the production of lactate, an oncometabolite, and also in anabolic reactions leading to the synthesis of fatty acids and cholesterol. The serine–glycine–one-carbon pathway is involved in the synthesis of purines and pyrimidines and the control of the epigenetic signature (DNA methylation, histone methylation) in cancer cells. Methionine is obligatory for most of the methyl-transfer reactions in the form of S-adenosylmethionine; here, too, the serine–glycine–one-carbon pathway is necessary for the resynthesis of methionine following the methyl-transfer reaction. Glutamine, serine, glycine, and methionine are obligatory to fuel these metabolic pathways. The first three amino acids can be synthesized endogenously to some extent, but the need for these amino acids in cancer cells is so high that they also have to be acquired from extracellular sources. Methionine is an essential amino acid, thus making it necessary for cancer cells to acquire this amino acid solely from the extracellular milieu. Cancer cells upregulate specific amino acid transporters to meet this increased demand for these four amino acids. SLC6A14 and SLC38A5 are the two transporters that are upregulated in a variety of cancers to mediate the influx of glutamine, serine, glycine, and methionine into cancer cells. SLC6A14 is a Na⁺/Cl⁻ -coupled transporter for multiple amino acids, including these four amino acids. In contrast, SLC38A5 is a Na⁺-coupled transporter with rather restricted specificity towards glutamine, serine, glycine, and methionine. Both transporters exhibit unique functional features that are ideal for the rapid proliferation of cancer cells. As such, these two amino acid transporters play a critical role in promoting the survival and growth of cancer cells and hence represent novel, hitherto largely unexplored, targets for cancer therapy.