Abstract
Lysosomes are known as key players in cellular signalling and act as terminal degradation stations involved in a multitude of cellular processes. Being a highly influential physiological factor, pH is essential in the regulation of lysosome-mediated physiological and pathological processes. Aberrant pH fluctuations are highly related to lysosomal dysfunction that correlates to lysosomal storage diseases and neurodegenerative disorders. As such, real-time quantitative monitoring of lysosomal pH (pHL) is crucial for gaining insight into lysosomal dysfunction but challenging by the lack of effective lysosome-specific probes with high signal fidelity. Toward this end, we have proposed a lysosomal fluorogenic nanoprobe (TR-MP) for reliable ratiometric measuring of pHL. It is fabricated by rational manipulation of fluorescence resonance energy transfer (FRET) in a tailorable nanoplatform. The nanoprobe consists of biocompatible silica nanoparticles assembled with a pH-sensitive rhodamine derivative (RDM-TEOS) as an acceptor and aggregation-induced emission (AIE) fluorophore (TPE-OMe) as a donor to ensure high energy transfer efficiency. Further equipped with cell-penetrating facilitator and morpholine to enable effective cell-internalization and high lysosome affinity of TR-MP. Results show that TR-MP can quantitatively measure pH in a range of 3.0 – 7.0 and detect pHL fluctuations in live cells under various stimuli, as well as real-time monitor pHL during apoptosis.
Highlights
As one of the vital organelles, lysosomes are key to cellular homeo stasis and the mediation of a variety of physiological processes, such as protein degradation, recycling damaged organelles, macromolecules digestion and plasma membrane repair [1,2,3,4]
Through rational designs and op timizations, this nanoplatform deservedly applies to achieve a ratio metric fluorogenic nanoprobe for the intended lysosomal pH sensing. We strategize such nanoprobe (TR-MP) where the fluorescence resonance energy transfer (FRET) is ach ieved by applying an aggregation-induced emission luminogens (AIEgens) as a donor, a pH-sensitive rhodamine derivates (RDMs) as an acceptor, the cell-permeability and the lysosomal specificity are imple mented by coupling cell-penetrating cyclic disulfides (CPCDs) and morpholinyl (MP), respectively
H+-induced ring-opening of spirocyclic structure of the xanthene in rhodamine B can restore intensive fluorescence, which can be effectively acted as an acceptor in a FRET system [36]
Summary
As one of the vital organelles, lysosomes are key to cellular homeo stasis and the mediation of a variety of physiological processes, such as protein degradation, recycling damaged organelles, macromolecules digestion and plasma membrane repair [1,2,3,4]. The ratio between two emission bands can be tuned by adjusting the proportions of the incorporated donor and acceptor It greatly enlarges the access of available fluo rophores and increases the flexibility to reach the requirements for an efficient FRET system, providing self-calibrated ratiometric signals for accurate detections. Through rational designs and op timizations, this nanoplatform deservedly applies to achieve a ratio metric fluorogenic nanoprobe for the intended lysosomal pH sensing We strategize such nanoprobe (TR-MP) where the FRET is ach ieved by applying an AIEgen as a donor, a pH-sensitive RDM as an acceptor, the cell-permeability and the lysosomal specificity are imple mented by coupling CPCDs and morpholinyl (MP), respectively. TR-MP has been successfully employed to quantitatively measure pHL in cells and to further track pHL fluctuations under various stimuli, including apoptosis induced by dexamethasone (Scheme 1)
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