A quantitative assay for lysosomal acidification rates in human osteoclasts

Ultraphotostable Phosphorescent Nanosensors for Sensing the Lysosomal pH at the Single-Cell Level over Long Durations

Ultraphotostable phosphorescent nanosensors have been designed for continuously sensing the lysosome pH over a long duration. The nanosensors exhibited excellent photostability, high accuracy, and capability to measure pH values during cell proliferation for up to 7 days. By arranging a metal-ligand complex of long phosphorescence lifetime and pH indicator in silica nanoparticles, we discover efficient Förster resonance energy transfer, which converts the pH-responsive UV-vis absorption signal of the pH indicator into a phosphorescent signal. Both the phosphorescent intensity and lifetime change at different pH values, and intracellular pH values can be accurately measured by our custom-built rapid phosphorescent lifetime imaging microscopy. The excellent photostability, high accuracy, and good biocompatibility prove that these nanosensors are a useful tool for tracing the fluctuation of pH values during endocytosis. The methodology can be easily adapted to design new nanosensors with different pKa or for different kinds of intracellular ions, as there are hundreds of pH and ion indicators readily available.

An optical assay of the transport activity of ClC-7

Osteoporosis, characterized by excessive osteoclast mediated bone resorption, affects millions of people worldwide representing a major public health problem. ClC-7 is a chloride-proton exchanger localized in lysosomes and in the resorption lacuna in osteoclasts where it is essential for bone resorption. Thus, drugs targeted at ClC-7 have been proposed for ameliorating osteoporosis. However, functional assays suited for high throughput screening (HTS) of ClC-7 function are lacking. Here we describe two complementary variants of purely optical assays of the transport activity of ClC-7, redirected to the plasma membrane employing a genetically encoded fluorescent Cl⁻/pH indicator fused to the ClC-7 protein. These simple and robust functional assays of ClC-7 transport are well-suited to be applied in HTS of small-molecule inhibitors and may help to develop drugs suited for the treatment of osteoporosis.

Extracellular matrix remodeling: the common denominator in connective tissue diseases. Possibilities for evaluation and current understanding of the matrix as more than a passive architecture, but a key player in tissue failure

Increased attention is paid to the structural components of tissues. These components are mostly collagens and various proteoglycans. Emerging evidence suggests that altered components and noncoded modifications of the matrix may be both initiators and drivers of disease, exemplified by excessive tissue remodeling leading to tissue stiffness, as well as by changes in the signaling potential of both intact matrix and fragments thereof. Although tissue structure until recently was viewed as a simple architecture anchoring cells and proteins, this complex grid may contain essential information enabling the maintenance of the structure and normal functioning of tissue. The aims of this review are to (1) discuss the structural components of the matrix and the relevance of their mutations to the pathology of diseases such as fibrosis and cancer, (2) introduce the possibility that post-translational modifications (PTMs), such as protease cleavage, citrullination, cross-linking, nitrosylation, glycosylation, and isomerization, generated during pathology, may be unique, disease-specific biochemical markers, (3) list and review the range of simple enzyme-linked immunosorbent assays (ELISAs) that have been developed for assessing the extracellular matrix (ECM) and detecting abnormal ECM remodeling, and (4) discuss whether some PTMs are the cause or consequence of disease. New evidence clearly suggests that the ECM at some point in the pathogenesis becomes a driver of disease. These pathological modified ECM proteins may allow insights into complicated pathologies in which the end stage is excessive tissue remodeling, and provide unique and more pathology-specific biochemical markers.