Monitoring the intracellular calcium response to a dynamic hypertonic environment

A programmable microfluidic platform to monitor calcium dynamics in microglia during inflammation

Neuroinflammation is characterized by the elevation of cytokines and adenosine triphosphate (ATP), which in turn activates microglia. These immunoregulatory molecules typically form gradients in vivo, which significantly influence microglial behaviors such as increasing calcium signaling, migration, phagocytosis, and cytokine secretion. Quantifying microglial calcium signaling in the context of inflammation holds the potential for developing precise therapeutic strategies for neurological diseases. However, the current calcium imaging systems are technically challenging to operate, necessitate large volumes of expensive reagents and cells, and model immunoregulatory molecules as uniform concentrations, failing to accurately replicate the in vivo microenvironment. In this study, we introduce a novel calcium monitoring micro-total analysis system (CAM-μTAS) designed to quantify calcium dynamics in microglia (BV2 cells) within defined cytokine gradients. Leveraging programmable pneumatically actuated lifting gate microvalve arrays and a Quake valve, CAM-μTAS delivers cytokine gradients to microglia, mimicking neuroinflammation. Our device automates sample handling and cell culture, enabling rapid media changes in just 1.5 s, thus streamlining the experimental workflow. By analyzing BV2 calcium transient latency to peak, we demonstrate location-dependent microglial activation patterns based on cytokine and ATP gradients, offering insights contrasting those of non-gradient-based perfusion systems. By harnessing advancements in microsystem technology to quantify calcium dynamics, we can construct simplified human models of neurological disorders, unravel the intricate mechanisms of cell-cell signaling, and conduct robust evaluations of novel therapeutics.

A Programmable Microfluidic Platform to Monitor Calcium Dynamics in Microglia during Inflammation

Calcium dynamics significantly influence microglial cell immune responses, regulating activation, migration, phagocytosis, and cytokine release. Understanding microglial calcium signaling is vital for insights into central nervous system immune responses and their impact on neuroinflammation. We introduce a calcium monitoring micro-total analysis system (CAM-μTAS) for quantifying calcium dynamics in microglia (BV2 cells) within defined cytokine microenvironments. The CAM-μTAS leverages the high efficiency pumping capabilities of programmable pneumatically actuated lifting gate microvalve arrays and the flow blocking capabilities of the Quake valve to deliver a cytokine treatment to microglia through a concentration gradient, therefore, biomimicking microglia response to neuroinflammation. Lifting gate microvalves precisely transfer a calcium indicator and culture medium to microglia cells, while the Quake valve controls the cytokine gradient. In addition, a method is presented for the fabrication of the device to incorporate the two valve systems. By automating the sample handling and cell culture using the lifting gate valves, we could perform media changes in 1.5 seconds. BV2 calcium transient latency to peak reveals location-dependent microglia activation based on cytokine and ATP gradients, contrasting non-gradient-based widely used perfusion systems. This device streamlines cell culture and quantitative calcium analysis, addressing limitations of existing perfusion systems in terms of sample size, setup time, and biomimicry. By harnessing advancements in microsystem technology to quantify calcium dynamics, we can construct simplified human models of neurological disorders, unravel the intricate mechanisms of cell-cell signaling, and conduct robust evaluations of novel therapeutics.

Review on optofluidic microreactors for photocatalysis

Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its fullest, a well-designed photoreactor is vital. Photocatalytic optofluidic microreactors, a promising technology that brings the merits of microfluidics to photocatalysis, offer the advantages of a large surface-to-volume ratio, a short molecular diffusion length and high reaction efficiency, providing a potential method for mitigating the aforementioned crises in the future. Although various photocatalytic optofluidic microreactors have been reported, a comprehensive review of microreactors applied to these four fields is still lacking. In this paper, we review the typical design and development of photocatalytic microreactors in the fields of water purification, water splitting, CO2 fixation and coenzyme regeneration in the past few years. As the most promising tool for solar energy utilization, we believe that the increasing innovation of photocatalytic optofluidic microreactors will drive rapid development of related fields in the future.

Optimizing Calcium Detection Methods in Animal Systems: A Sandbox for Synthetic Biology

Since the 1970s, the emergence and expansion of novel methods for calcium ion (Ca2+) detection have found diverse applications in vitro and in vivo across a series of model animal systems. Matched with advances in fluorescence imaging techniques, the improvements in the functional range and stability of various calcium indicators have significantly enhanced more accurate study of intracellular Ca2+ dynamics and its effects on cell signaling, growth, differentiation, and regulation. Nonetheless, the current limitations broadly presented by organic calcium dyes, genetically encoded calcium indicators, and calcium-responsive nanoparticles suggest a potential path toward more rapid optimization by taking advantage of a synthetic biology approach. This engineering-oriented discipline applies principles of modularity and standardization to redesign and interrogate endogenous biological systems. This review will elucidate how novel synthetic biology technologies constructed for eukaryotic systems can offer a promising toolkit for interfacing with calcium signaling and overcoming barriers in order to accelerate the process of Ca2+ detection optimization.

Cell Deformation at the Air-Liquid Interface Evokes Intracellular Ca2+ Increase and ATP Release in Cultured Rat Urothelial Cells

Urothelial cells have been implicated in bladder mechanosensory transduction, and thus, initiation of the micturition reflex. Cell deformation caused by tension forces at an air-liquid interface (ALI) can induce an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and ATP release in some epithelial cells. In this study, we aimed to examine the cellular mechanisms underlying ALI-induced [Ca²⁺]_i increase in cultured urothelial cells. The ALI was created by stopping the influx of the perfusion but maintaining efflux. The [Ca²⁺]_i increase was measured using the Ca²⁺ imaging method. The ALI evoked a reversible [Ca²⁺]_i increase and ATP release in urothelial cells, which was almost abolished by GdCl₃. The specific antagonist of the transient receptor potential vanilloid (TRPV4) channel (HC0674) and the antagonist of the pannexin 1 channel (¹⁰panx) both diminished the [Ca²⁺]_i increase. The blocker of Ca²⁺-ATPase pumps on the endoplasmic reticulum (thapsigargin), the IP3 receptor antagonist (Xest-C), and the ryanodine receptor antagonist (ryanodine) all attenuated the [Ca²⁺]_i increase. Degrading extracellular ATP with apyrase or blocking ATP receptors (P2X or P2Y) with pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) significantly attenuated the [Ca²⁺]_i increase. Our results suggest that both Ca²⁺ influx via TRPV4 or pannexin 1 and Ca²⁺ release from intracellular Ca²⁺ stores via IP3 or ryanodine receptors contribute to the mechanical responses of urothelial cells. The release of ATP further enhances the [Ca²⁺]_i increase by activating P2X and P2Y receptors via autocrine or paracrine mechanisms.

Hypertonicity counteracts MCL-1 and renders BCL-XL a synthetic lethal target in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is an aggressive and difficult-to-treat cancer entity. Current therapies ultimately aim to activate the mitochondria-controlled (intrinsic) apoptosis pathway, but complex alterations in intracellular signaling cascades and the extracellular microenvironment hamper treatment response. On the one hand, proteins of the BCL-2 family set the threshold for cell death induction and prevent accidental cellular suicide. On the other hand, controlling a cell's readiness to die also determines whether malignant cells are sensitive or resistant to anticancer treatments. Here, we show that HNSCC cells upregulate the proapoptotic BH3-only protein NOXA in response to hyperosmotic stress. Induction of NOXA is sufficient to counteract the antiapoptotic properties of MCL-1 and switches HNSCC cells from dual BCL-XL/MCL-1 protection to exclusive BCL-XL addiction. Hypertonicity-induced functional loss of MCL-1 renders BCL-XL a synthetically lethal target in HNSCC, and inhibition of BCL-XL efficiently kills HNSCC cells that poorly respond to conventional therapies. We identify hypertonicity-induced upregulation of NOXA as link between osmotic pressure in the tumor environment and mitochondrial priming, which could perspectively be exploited to boost efficacy of anticancer drugs.

Two-photon microscopy assessment of the overall energy metabolism alteration of amoeba in hypertonic environment

In this study, a two-photon fluorescence microscopic imaging technique is reported for assessment the effect of dynamic hypertonic environment on the overall energy metabolism alteration and adaptation of soil-living amoeba Dictyostelium discoideum. For that purpose the fluorescence intensity of mitochondrial reduced nicotinamide adenine dinucleotide (NADH) was monitored and quantified in order to evaluate the corresponded metabolic state of monolayer cultured cells. The two-photon excitation of NADH with 720 nm near infrared irradiation produced blue fluorescence emission with maximum wavelength centered at 460 nm. The benefits of reported noninvasive microscopic technique are the significantly less cellular damage and avoiding the excitation of other biomolecules except of NADH. It enabled to acquire data for NADH levels of the observed cells on agar plate specimen and hypertonic nutrition media in a Petri dish. The method demonstrated also good sensitivity, reproducibility and the obtained results revealed that D. discoideum species form aggregation in hypertonic environment within several minutes with aim to survive. The formed aggregate had amorphous shape and it consisted from dozen amoeba cells, which kept their NADH amount in constant level for few hours. The reported imaging method might be applicable in various studies for characterization of metabolic events and assessment of the cell energy balance in hypertonic environment.

Review on optofluidic microreactors for artificial photosynthesis

Artificial photosynthesis (APS) mimics natural photosynthesis (NPS) to store solar energy in chemical compounds for applications such as water splitting, CO2 fixation and coenzyme regeneration. NPS is naturally an optofluidic system since the cells (typical size 10 to 100 µm) of green plants, algae, and cyanobacteria enable light capture, biochemical and enzymatic reactions and the related material transport in a microscale, aqueous environment. The long history of evolution has equipped NPS with the remarkable merits of a large surface-area-to-volume ratio, fast small molecule diffusion and precise control of mass transfer. APS is expected to share many of the same advantages of NPS and could even provide more functionality if optofluidic technology is introduced. Recently, many studies have reported on optofluidic APS systems, but there is still a lack of an in-depth review. This article will start with a brief introduction of the physical mechanisms and will then review recent progresses in water splitting, CO2 fixation and coenzyme regeneration in optofluidic APS systems, followed by discussions on pending problems for real applications.

Microfluidic chip-based one-step fabrication of an artificial photosystem I for photocatalytic cofactor regeneration

We report a one-step strategy for the formation of an artificial photosystem I, with an enhanced coenzyme regeneration rate.