Endoplasmic Reticulum-targeting Fluorescent Probe Research Articles

Fluorescence Imaging of Intracellular Glutathione Levels in the Endoplasmic Reticulum to Reveal the Inhibition Effect of Rutin on Ferroptosis.

Ferroptosis is an emerging form of nonapoptotic cell death, and the search for novel ferroptosis inhibitors is of great importance to explore unique cytoprotective strategies against ferroptosis-relevant diseases. In this work, we present an endoplasmic reticulum-targeting fluorescent probe (ER-G) for the imaging of intracellular glutathione (GSH) levels and revealed the inhibition effect of rutin on ferroptosis. Structurally, ER-G utilized a cyclohexyl sulfonylurea as the endoplasmic reticulum-targeting unit, and single-crystal X-ray diffraction analysis confirmed that ER-G possessed a N-oxide pyridine sulfinyl group instead of sulfone. After the response of ER-G to GSH, the fluorescence intensity at 523 nm displayed a significant increase by 3900-fold. ER-G showed extreme sensitivity and selectivity to GSH. The fluorescence imaging results demonstrated that ER-G exhibited excellent endoplasmic reticulum-targeting properties and could be applied to monitor GSH levels in the endoplasmic reticulum during the erastin-induced ferroptosis process. By the fluorescence imaging of GSH levels in the endoplasmic reticulum, it was demonstrated that rutin could efficiently block the depletion of GSH during erastin-induced ferroptosis and potentially act as a novel ferroptosis inhibitor. Moreover, unlike traditional ferroptosis inhibitors, it was speculated that the inhibition mechanism of rutin to ferroptosis was the integration of the chelate effect on Fe(II) ions and antioxidant effect. We expect that fluorescence imaging of GSH levels in the endoplasmic reticulum could provide a convenient and feasible method to evaluate the inhibition effect of small molecules on ferroptosis.

Real-time monitoring norepinephrine exocytosis by high K+via an endoplasmic reticulum-targeting fluorescent probe.

Norepinephrine (NE), a neurotransmitter, has multiple functions in the neural system and peripheral organs. Abnormal levels of NE may lead to numerous neuro-degenerative and psychiatric disorders, such as Parkinson's disease, depression and Alzheimer's disease. Moreover, studies have indicated that an increase in NE may induce endoplasmic reticulum (ER) stress and cell apoptosis via oxidative stress. Therefore, developing a measure to monitor NE levels in the ER appears to be particularly important. The fluorescence imaging technique has become an ideal tool for detecting various biological molecules in situ, with the advantages of high selectivity, nondestructive testing, and real-time dynamic monitoring. However, there are currently no activatable ER fluorescent probes that can be used to monitor NE levels in the ER. Herein, a robust ER-targetable fluorescence probe (ER-NE) for detecting NE in the ER was constructed for the first time. With the excellent properties of high selectivity, low cytotoxicity and good biocompatibility for NE detection, ER-NE successfully achieved the detection of endogenous and exogenous NE under physiological conditions. More importantly, a probe was further applied to monitor NE exocytosis stimulated by continuous incubation with high K+. We expect that the probe may serve as a powerful tool for detecting NE and provide a potential new diagnostic method for related neurodegenerative diseases.

Development of an Endoplasmic Reticulum-targeting Fluorescent Probe for the Imaging of Superoxide Anion in Living Cells.

Superoxide anion (O2•-) is an important reactive oxygen species (ROS), and plays critical roles in biological systems. ER stress has close relation with many metabolic diseases, and could lead to the abnormal production of ROS including O2•-. Herein, we present an ER-targeting probe (ER-Tf) for the detection of O2•- in living cells. The probe ER-Tf used triflate as the response site for O2•-, and employed p-methylbenzenesulfonamide as ER-targeting moiety. In response to O2•-, the triflate of the probe ER-Tf converted to hydroxyl group, providing strong blue emission under the excitation of ultraviolet light. The probe ER-Tf exhibited high sensitivity and selectivity to O2•-. Bioimaging experiments showed that the probe ER-Tf can be applied to detect O2•- at ER, and also demonstrated that rotenone could increase the generation of O2•- in living cells, while the O2•- level at ER showed no remarkable change during ferroptosis.

An endoplasmic reticulum-targeting fluorescent probe for the visualization of the viscosity fluctuations during ferroptosis in live cells

Ferroptosis is an unique iron-dependent cell death form and currently has been shown to closely relate with ER. Revealing the viscosity fluctuations of ER during ferroptosis is of great significance not only to monitor the occurrence and development of iron poisoning, but also to deeply understand the biological effects of ER in ferroptosis. Herein, we present an ER-targeting fluorescent probe (PV1) to detect viscosity changes of ER during ferroptosis. PV1 utilized a rotatable C–C bond to connect the two rigid π-systems, and responded viscosity by the regulation of the coplanarity of these two planes. PV1 displayed desirable sensitivity and selectivity to viscosity. The biological imaging results suggested that PV1 mainly distributed at ER in live cells, and the viscosity of ER exhibited an evident increase in the process of erastin-induced ferroptosis. After the simultaneous incubation of cells with erastin and Fer-1 or VE, the viscosity of ER showed no marked change, and it suggested that the erastin-induced ferroptosis could be inhibited by Fer-1 and VE. We expect that the developed probe could provide a feasible and rapid method for the in-depth study of the ferroptosis-based disease treatment and drug design.

The development of an endoplasmic reticulum-targeting fluorescent probe for the imaging of 1,4-dithiothreitol (DTT) in living cells.

1,4-Dithiothreitol (DTT) is a robust reducing agent that contributes significantly to the folding process of proteins and maintaining endoplasmic reticulum (ER) homeostasis. Abnormally high levels of DTT can lead to severe endoplasmic reticulum stress (ERS), which induces cell death. In addition, DTT can also hinder cell growth and enhance reactive oxygen species (ROS) production in the ER. Herein, an effective turn-on ER-targeting fluorescent probe, ER-DTT, was designed to image DTT for the first time. The probe ER-DTT was based upon naphthalimide as a fluorophore, p-toluenesulfonamide as an exceptional unit for ER-targeting, and sulfoxide as a response site for imaging DTT based on an intramolecular charge transfer (ICT) mechanism. Optical-response experiments showed that the probe ER-DTT had good selectivity and sensitivity for DTT. Furthermore, confocal microscopy indicated that ER-DTT was suitable for selectively targeting ER in living cells and could be implemented to recognize cellular DTT.

An endoplasmic reticulum-targeting fluorescent probe for discriminatory detection of Cys, Hcy and GSH in living cells

Endoplasmic reticulum, known to us as the ER, is the largest organelle in many kinds of eukaryotic cells and plays vital roles in maintaining the normal function of cells. Biothiols (Cys, Hcy, GSH) in secretory proteins will be modified as they enter the ER and are of great importance in balancing redox state of ER environments. In this article, we have developed the first endoplasmic reticulum-targeting fluorescent probe, ER-CP, for concurrent distinguishment of Cys, Hcy and GSH with favorable sensitivity and selectivity. ER-CP was successfully used in fluorescence imaging of Cys, Hcy and GSH in HeLa cells. In addition, ER-CP exhibited a good ER-targeting property (Pearson’s correlation coefficient = 0.90).

A highly sensitive endoplasmic reticulum-targeting fluorescent probe for the imaging of endogenous H2S in live cells.

Hydrogen sulfide (H2S) as an important signaling biomolecule participates in a series of complex physiological and pathological processes. In situ and rapid detection of H2S levels in endoplasmic reticulum (ER) is of great importance for the in-depth study of its virtual functional roles. However, the ER-targeting fluorescent probe for the detection of H2S in live cells is still quite rare. Herein, a new ER-targeting fluorescent probe (FER-H2S) for detecting H2S in live cells was characterized in the present study. This probe FER-H2S was built from the hybridization of three parts, including fluorescein-based skeleton, p-toluenesulfonamide as ER-specific group, and 2,4-nitrobenzene sulfonate as a response site for H2S. The response mechanism of the probe FER-H2S to H2S is on the basis of the ring-opening and ring-closing processes in fluorescein moiety. Moreover, the probe FER-H2S was successfully used for the imaging of exogenous and endogenous H2S in ER of live cells.

An endoplasmic reticulum-targeting fluorescent probe for imaging ˙OH in living cells.

The hydroxyl radical (˙OH) in the endoplasmic reticulum has not been studied thoroughly due to the lack of proper methods. Here, an endoplasmic reticulum-targeting fluorescent probe for detecting ˙OH is reported. With this probe, the action of ˙OH in the endoplasmic reticulum has been imaged in living cells.

An endoplasmic reticulum-targeting fluorescent probe for the imaging of hypochlorous acid in living cells and zebrafishes

Hypochlorous acid (HClO) plays critical biological roles in living systems, and abnormal accumulation of HClO could cause oxidative stress and lead to tissue damage and a range of diseases. Herein, we present an endoplasmic reticulum (ER)-targeting fluorescent probe (ER-NTE) for the detection of HClO in live cells and zebrafishes. The probe ER-NTE employed p-toluenesulfonamide as the ER-specific group, and used N,N-dimethylthiocarbamate as the recognition site for HClO. In response to HClO, the probe ER-NTE provided significant turn-on fluorescence signal (60-fold enhancement) within 2 min. Biological imaging experiments suggested that ER-NTE could specifically image exogenous and endogenous HClO in ER of living cells, and also could be applied for the detection of HClO in zebrafishes.

Development of an endoplasmic reticulum-targeting fluorescent probe for the imaging of polarity in living cells and tissues

Cell polarity is one of the important parameters of the biological microenvironment, and controls the synthesis of functional proteins.

An endoplasmic reticulum-targeting fluorescent probe for the imaging of GSH in living cells

A new endoplasmic reticulum (ER)-targeting fluorescent probe (ER-G) was designed and applied for the detection of cellular GSH in the ER.

Development of an endoplasmic reticulum-targeting fluorescent probe for the two-photon imaging of hypochlorous acid (HClO) in living cells

As an important reactive oxygen species, hypochlorous acid (HClO) could irreversibly destroy Ca2+-ATPase to inhibit Ca2+transport in the endoplasmic reticulum (ER), which may eventually lead to cell dysfunction and cell death.

Recent Progress on Endoplasmic Reticulum-Targetable Fluorescence Probe

Recent Progress on Endoplasmic Reticulum-Targetable Fluorescence Probe

A two-photon endoplasmic reticulum-targeting fluorescent probe for the imaging of pH in living cells and zebrafish

The pH changes of the endoplasmic reticulum (ER) are closely related to many diseases.