In vitro catabolic effect of protoporphyrin IX in human osteoblast-like cells: possible role of the 18 kDa mitochondrial translocator protein

O-GlcNAcylation regulates osteoblast differentiation through the morphological changes in mitochondria, cytoskeleton, and endoplasmic reticulum

To explore the potential mechanisms which O-linked-N-acetylglucosaminylation (O-GlcNAcylation) regulates osteogenesis, a publicly RNA-seq dataset was re-analyzed with literature-mining and showed the primary targets of O-GlcNAcylation in osteoblasts are mitochondria/cytoskeleton. Although the O-GlcNAcylation-regulated mitochondria/cytoskeleton has been extensively studied, its specific role during osteogenesis remains unclear. To address this, we knocked out Ogt (Ogt-KO) in MC3T3-E1 osteoblastic cells. Then, significantly reduced osteoblast differentiation, motility, proliferation, mitochondria-endoplasmic reticulum (Mito-ER) coupling, volume of ER, nuclear tubulins, and oxygen metabolism were observed in Ogt-KO cells. Through artificial intelligence (AI)-predicted cellular structures, the time-lapse live cells imaging with reactive-oxygen-species/hypoxia staining showed that lower cell proliferation and altered oxygen metabolism in the Ogt-KO cells were correlated with the Mito-ER coupling. Bioinformatics analysis, combined with correlated mRNA and protein expression, suggested that Ezh2 and its downstream targets (Opa1, Gsk3a, Wnt3a, Hif1a, and Hspa9) may be involved in O-GlcNAcylation-regulated Mito-ER coupling, ultimately impacting osteoblast differentiation. In conclusion, our findings indicate that O-GlcNAcylation-regulated osteoblast differentiation is linked to morphological changes in mitochondria, cytoskeleton, and ER, with Ezh2 potentially playing a crucial role.

Red-emitting carbon nanoparticles with unprecedented singlet oxygen generation efficiency for cancer theranostics

Fluorescent Red-emitting carbon nanoparticles (RCNPs) are produced by an economical and green hydrothermal method using Eucalyptus leaves as a precursor. This is the first report of its kind demonstrating RCNPs in combined PDT-Chemo combination therapy, as RCNPs bind with mitoxantrone (MTO) electrostatically. The synthesized RCNPs before and after conjugation of MTO are characterised using DLS, SEM, TEM, UV-Vis, Fluorescence, FTIR, and ¹H NMR Spectroscopy. FTIR and ¹H NMR confirm the interaction between -NH proton of MTO with carboxylic acid oxygen of RCNPs. RCNPs are demonstrated as brightly fluorescent, type II photosensitizer (PS) with an extraordinary ¹O₂ quantum yield of 0.96, when triggered with a red laser at 660 nm. Moreover, the biocompatibility of RCNPs and RCNPs-MTO are examined and confirmed by performing a cytotoxicity assay on MCF-7 cell lines. Subsequently, to explore the internalization process of the RCNPs as a function of concentration, confocal imaging study is also carried out. The cell viability and the apoptosis assay indicates that RCNPs-MTO can achieve the PDT-Chemo synergistic cancer therapy. To the best of our knowledge, this is the first time that Eucalyptus leaves, a natural source of great abundance, is used as raw material and applied for combined PDT-chemotherapy.

The Role of Translocator Protein TSPO in Hallmarks of Glioblastoma

Simple Summary

The translocator protein (TSPO) has been under extensive investigation as a specific marker in positron emission tomography (PET) to visualize brain lesions following injury or disease. In recent years, TSPO is increasingly appreciated as a potential novel therapeutic target in cancer. In Glioblastoma (GBM), the most malignant primary brain tumor, TSPO expression levels are strongly elevated and scientific evidence accumulates, hinting at a pivotal role of TSPO in tumorigenesis and glioma progression. The aim of this review is to summarize the current literature on TSPO with respect to its role both in diagnostics and especially with regard to the critical hallmarks of cancer postulated by Hanahan and Weinberg. Overall, our review contributes to a better understanding of the functional significance of TSPO in Glioblastoma and draws attention to TSPO as a potential modulator of treatment response and thus an important factor that may influence the clinical outcome of GBM.

Abstract

Glioblastoma (GBM) is the most fatal primary brain cancer in adults. Despite extensive treatment, tumors inevitably recur, leading to an average survival time shorter than 1.5 years. The 18 kDa translocator protein (TSPO) is abundantly expressed throughout the body including the central nervous system. The expression of TSPO increases in states of inflammation and brain injury due to microglia activation. Not least due to its location in the outer mitochondrial membrane, TSPO has been implicated with a broad spectrum of functions. These include the regulation of proliferation, apoptosis, migration, as well as mitochondrial functions such as mitochondrial respiration and oxidative stress regulation. TSPO is frequently overexpressed in GBM. Its expression level has been positively correlated to WHO grade, glioma cell proliferation, and poor prognosis of patients. Several lines of evidence indicate that TSPO plays a functional part in glioma hallmark features such as resistance to apoptosis, invasiveness, and proliferation. This review provides a critical overview of how TSPO could regulate several aspects of tumorigenesis in GBM, particularly in the context of the hallmarks of cancer proposed by Hanahan and Weinberg in 2011.

Biosensor device for the photo-specific detection of immuno-captured bladder cancer cells using hexaminolevulinate: An ex-vivo study

Exogenous administration of the photodynamic agent hexaminolevulinate induces Protoporphyrin IX (PpIX) accumulation in malignant tissue. This may enable differentiation from healthy tissues by emission of a distinctive red fluorescence. It provides the photo-specific detection when excited with blue light at 405 nm. This study determines the ex-vivo processing conditions (time, concentration, temperature and addition of a fluorescent dye) required for HAL-induced PpIX fluorescence to successfully discriminate between bladder cancer and benign fibroblast cells shed in urine at the single cell level. HAL-induced fluorescence was 4.5 times brighter in cancer cells than non-cancer cells when incubated in the optimum conditions, and could be used to correctly identified bladder cancer cells captured within a newly developed immunofunctionalized biosensor with 88% efficiency. This biosensor is designed to facilitate the immuno-capture of cancer cells by interaction with carcinoma specific anti Epithelial Cell Adhesion molecule (anti-EpCAM) antibodies. Anti-EpCAM antibodies were immobilized on polyoxazoline (POx) plasma polymers by covalent bonds in microfluidic channels. Combining photodynamic and immunoselective approach therefore constitute a promising approach for the non-invasive diagnosis of bladder cancer with two independent level of confidence.

OBJECTIVE

This study investigate the relationship between different regulatory factors (time, concentration, temperature and addition of a fluorescent dye) and Hexaminolevulinate (HAL)-mediated photodynamic diagnosis of bladder cancer (PDD) in vitro. We examine the natural photosensitizer Protoporphyrin IX (PpIX) fluorescence induced by HAL in several human bladder cancer cell lines and one non-cancer foreskin fibroblast cell line and identify the processing conditions that maximise the difference in fluorescence intensity between malign and benign cell types. The detection of HAL induced fluorescence at a single cell level by a selective cancer cell capture platform is also tested.

MATERIALS AND METHODS

Experiments were performed on cultured monolayer cells and cells in suspension. The cell lines examined included the transitional epithelium carcinoma cell lines HT1197, HT1376, EJ138 and RT4, and the non-cancer foreskin fibroblasts HFF. Cells were incubated with HAL in various doses, time and temperature settings. We also used the nuclear red as a tool to study the PpIX subcellular localization. PpIX fluorescence intensities were measured and analysed using fluorescence microscope software. Finally, we evaluated the possibility of using HAL to discriminate between cancer and non-cancer cells from a mixed cell population using a newly developed immunofunctionalized microfluidic platform.

RESULTS

The accumulation of PpIX in bladder cancer cells was significantly higher than in non-cancer cells, both cultured monolayer cells and cells in suspension. Effectively, the fluorescence intensity was 4.5 times brighter in bladder cancer cells than non-cancer foreskin fibroblast cells when incubated in the optimum condition, in which the nuclear stain adjuvant acted as a fluorescence enhancer. Cancer cells displayed PpIX accumulated mainly in mitochondria but none or very little PpIX was observed in non-cancer cells. HAL-induced fluorescence could be used to correctly identify bladder cancer cells within the EpCAM conjugated POx based microfluidic sensor with an 88% capture selectivity rate.

CONCLUSIONS

These findings prove that the application of HAL-induced PpIX fluorescence can successfully distinguish between cancer and non-cancer cells in vitro. This test can provide advanced second level of confidence on the cancerous nature of cells captured by the immunofunctionalized bladder cancer diagnostic platform.

Regulation of Mitochondrial, Cellular, and Organismal Functions by TSPO

In 1999, the enigma of the 18kDa mitochondrial translocator protein (TSPO), also known as the peripheral-type benzodiazepine receptor, was the seeming disparity of the many functions attributed to TSPO, ranging from the potential of TSPO acting as a housekeeping gene at molecular biological levels to adaptations to stress, and even involvement in higher emotional and cognitive functioning, such as anxiety and depression. In the years since then, knowledge regarding the many functions modulated by TSPO has expanded, and understanding has deepened. In addition, new functions could be firmly associated with TSPO, such as regulation of programmed cell death and modulation of gene expression. Interestingly, control by the mitochondrial TSPO over both of these life and death functions appears to include Ca⁺⁺ homeostasis, generation of reactive oxygen species (ROS), and ATP production. Other mitochondrial functions under TSPO control are considered to be steroidogenesis and tetrapyrrole metabolism. As TSPO effects on gene expression and on programmed cell death can be related to the wide range of functions that can be associated with TSPO, several of these five elements of Ca⁺⁺, ROS, ATP, steroids, and tetrapyrroles may indeed form the basis of TSPO's capability to operate as a multifunctional housekeeping gene to maintain homeostasis of the cell and of the whole multicellular organism.

Functional gains in energy and cell metabolism after TSPO gene insertion

Recent loss-of-function studies in tissue-specific as well as global Tspo (Translocator Protein 18 kDa) knockout mice have not confirmed its long assumed indispensability for the translocation of cholesterol across the mitochondrial inter-membrane space, a rate-limiting step in steroid biosynthesis. Instead, recent studies in global Tspo knockout mice indicate that TSPO may play a more fundamental role in cellular bioenergetics, which may include the indirect down-stream regulation of transport or metabolic functions. To examine whether overexpression of the TSPO protein alters the cellular bioenergetic profile, Jurkat cells with low to absent endogenous expression were transfected with a TSPO construct to create a stable cell line with de novo expression of exogenous TSPO protein. Expression of TSPO was confirmed by RT-qPCR, radioligand binding with [3H]PK11195 and immunocytochemistry with a TSPO antibody. We demonstrate that TSPO gene insertion causes increased transcription of genes involved in the mitochondrial electron transport chain. Furthermore, TSPO insertion increased mitochondrial ATP production as well as cell excitability, reflected in a decrease in patch clamp recorded rectified K channel currents. These functional changes were accompanied by an increase in cell proliferation and motility, which were inhibited by PK11195, a selective ligand for TSPO. We suggest that TSPO may serve a range of functions that can be viewed as downstream regulatory effects of its primary, evolutionary conserved role in cell metabolism and energy production.

Tetrapyrroles as Endogenous TSPO Ligands in Eukaryotes and Prokaryotes: Comparisons with Synthetic Ligands

The 18 kDa translocator protein (TSPO) is highly 0conserved in eukaryotes and prokaryotes. Since its discovery in 1977, numerous studies established the TSPO’s importance for life essential functions. For these studies, synthetic TSPO ligands typically are applied. Tetrapyrroles present endogenous ligands for the TSPO. Tetrapyrroles are also evolutionarily conserved and regulate multiple functions. TSPO and tetrapyrroles regulate each other. In animals TSPO-tetrapyrrole interactions range from effects on embryonic development to metabolism, programmed cell death, response to stress, injury and disease, and even to life span extension. In animals TSPOs are primarily located in mitochondria. In plants TSPOs are also present in plastids, the nuclear fraction, the endoplasmic reticulum, and Golgi stacks. This may contribute to translocation of tetrapyrrole intermediates across organelles’ membranes. As in animals, plant TSPO binds heme and protoporphyrin IX. TSPO-tetrapyrrole interactions in plants appear to relate to development as well as stress conditions, including salt tolerance, abscisic acid-induced stress, reactive oxygen species homeostasis, and finally cell death regulation. In bacteria, TSPO is important for switching from aerobic to anaerobic metabolism, including the regulation of photosynthesis. As in mitochondria, in bacteria TSPO is located in the outer membrane. TSPO-tetrapyrrole interactions may be part of the establishment of the bacterial-eukaryote relationships, i.e., mitochondrial-eukaryote and plastid-plant endosymbiotic relationships.

TSPO: kaleidoscopic 18-kDa amid biochemical pharmacology, control and targeting of mitochondria

The 18-kDa translocator protein (TSPO) localizes in the outer mitochondrial membrane (OMM) of cells and is readily up-regulated under various pathological conditions such as cancer, inflammation, mechanical lesions and neurological diseases. Able to bind with high affinity synthetic and endogenous ligands, its core biochemical function resides in the translocation of cholesterol into the mitochondria influencing the subsequent steps of (neuro-)steroid synthesis and systemic endocrine regulation. Over the years, however, TSPO has also been linked to core cellular processes such as apoptosis and autophagy. It interacts and forms complexes with other mitochondrial proteins such as the voltage-dependent anion channel (VDAC) via which signalling and regulatory transduction of these core cellular events may be influenced. Despite nearly 40 years of study, the precise functional role of TSPO beyond cholesterol trafficking remains elusive even though the recent breakthroughs on its high-resolution crystal structure and contribution to quality-control signalling of mitochondria. All this along with a captivating pharmacological profile provides novel opportunities to investigate and understand the significance of this highly conserved protein as well as contribute the development of specific therapeutics as presented and discussed in the present review.

Protein structure. Structure and activity of tryptophan-rich TSPO proteins

Translocator proteins (TSPOs) bind steroids and porphyrins, and they are implicated in many human diseases, for which they serve as biomarkers and therapeutic targets. TSPOs have tryptophan-rich sequences that are highly conserved from bacteria to mammals. Here we report crystal structures for Bacillus cereus TSPO (BcTSPO) down to 1.7 Å resolution, including a complex with the benzodiazepine-like inhibitor PK11195. We also describe BcTSPO-mediated protoporphyrin IX (PpIX) reactions, including catalytic degradation to a previously undescribed heme derivative. We used structure-inspired mutations to investigate reaction mechanisms, and we showed that TSPOs from Xenopus and man have similar PpIX-directed activities. Although TSPOs have been regarded as transporters, the catalytic activity in PpIX degradation suggests physiological importance for TSPOs in protection against oxidative stress.

The translocator protein as a potential molecular target for improved treatment efficacy in photodynamic therapy

Since its serendipitous discovery over 30 years ago, the translocator protein (18 kDa) has been demonstrated to play an important role in a multitude of critical biological processes. Although implemented as a novel therapeutic and diagnostic tool for a variety of disease states, its most promising role is as a molecular target for anticancer treatments such as photodynamic therapy (PDT). This review gives an overview of the attempts made by researchers to design porphyrin-based photosensitizers for use as anticancer therapeutics in PDT as well as improved imaging agents for diagnostic purposes. With a better understanding of the structure and function of the translocator protein, the synthesis of porphyrins for use in PDT with optimum binding affinities will become ever more possible.