The mitochondrial translocator protein (TSPO, 18 kDa): A key multifunctional molecule in liver diseases

TSPO participates in the pathogenesis of diabetic periodontitis related to mitophagy

OBJECTIVES

Diabetic periodontitis (DP) appears to be the sixth most common complication of diabetes; however, its underlying pathological mechanisms require further explored. Our study investigated the potential function of the translocator protein (TSPO) in the progression of DP, aiming to provide a theoretical foundation for novel treatment strategies.

METHODS

The ultrastructure and TSPO expression of gingival tissue, collected from healthy individuals, people with periodontitis, and those with DP, were examined. In vivo, a DP model in rats was established using streptozotocin (STZ) and silk ligation. TSPO ligand antagonist PK 11195 was administered as a treatment. Microcomputed tomography (Micro-CT), quantitative real-time polymerase chain reaction (qPCR), histology and immunohistochemistry were employed to assess the destruction, inflammatory and mitophagy in rat periodontal tissues. In in vitro experiments, the inflammatory responses, mitochondrial function, mitophagy and the potential role of TSPO in macrophages were also examined under high-glucose inflammatory conditions, using flow cytometry, fluorescence probes, qPCR, Western blotting and transcription inhibition.

RESULTS

Mitochondrial damage, mitophagy inhibition and increased TSPO expression were observed in gingivae from patients with DP. PK 11195 facilitated the restoration of mitophagy and alleviated the inflammatory destruction of DP rats. Additionally, the high-glucose inflammatory environment intensified the macrophage inflammatory response, ROS production, and mitochondrial damage. These pathological changes were reduced by TSPO inhibition, which could also upregulate the mitophagy.

CONCLUSIONS

The inflammation and destruction of periodontal tissue in DP are closely linked to mitophagy associated with TSPO. Immunotherapy targeting TSPO in macrophages could significantly influence the treatment of DP by modulating mitophagy.

Tspo Depletion Exacerbates Steatosis Through Fatty Acid Uptake

Previous studies demonstrated that Tspo loss causes simple steatosis (SS) in hepatocytes in vitro. However, its effect on SS in vivo remains unclear. In this study, we hypothesise that Tspo loss promotes early-stage MASLD. WT and Tspo KO rats were fed a Gubra Amylin NASH (GAN) diet for 8 weeks to induce SS. Tspo KO rats fed the GAN diet (KO GAN) exhibited increased insulin resistance, higher plasma cholesterol, and elevated hepatic triacylglycerol (TAG) levels, along with higher de novo lipogenesis (DNL) and free fatty acid (FFA) uptake, evidenced by increased fatty acid synthase (FASN) and CD36 expression. The Acyl-coenzyme A binding protein/diazepam-binding inhibitor-TSPO complex facilitated FA transport to the mitochondria, where carnitine palmitoyltransferase 1A (CPT1A) directed them for β-oxidation. TSPO interacted with CPT1A in the outer mitochondrial membrane, while its depletion increased CPT1A expression, boosting FA oxidation. Primary Tspo KO rat hepatocytes and stably overexpressed CD36 (CD36_OE) in Huh7 cells displayed impaired mitochondrial function and compromised mitochondrial membrane potential. KO GAN livers had significantly elevated AcCoA, which acetylated RAPTOR, activating mTORC1 to suppress autophagy. Overall, Tspo deficiency exacerbates the advancement of SS by enhancing CD36-mediated FFA uptake, elevating AcCoA levels, compromising mitochondrial function and impairing autophagy during the early stages of MASLD.

Fighting Cancer with Photodynamic Therapy and Nanotechnologies: Current Challenges and Future Directions

Photodynamic therapy (PDT) is an innovative treatment that has recently been approved for clinical use and holds promise for cancer patients. It offers several benefits, such as low systemic toxicity, minimal invasiveness, and the ability to stimulate antitumor immune responses. For certain types of cancer, it has shown positive results with few side effects. However, PDT still faces some challenges, including limited light penetration into deeper tumor tissues, uneven distribution of the photosensitizer (PS) that can also affect healthy cells, and the difficulties posed by the hypoxic tumor microenvironment (TME). In hypoxic conditions, PDT's effectiveness is reduced due to insufficient production of reactive oxygen species, which limits tumor destruction and can lead to relapse. This review highlights recent advances in photosensitizers and nanotechnologies that are being developed to improve PDT. It focuses on multifunctional nanoplatforms and nanoshuttles that have shown promise in preclinical studies, especially for treating solid tumors. One of the key areas of focus is the development of PSs that specifically target mitochondria to treat deep-seated malignant tumors. New mitochondria-targeting nano-PSs are designed with better water solubility and extended wavelength ranges, allowing them to target tumors more effectively, even in challenging, hypoxic environments. These advancements in PDT are opening new doors for cancer treatment, especially when combined with other therapeutic strategies. Moving forward, research should focus on optimizing PDT, creating more efficient drug delivery systems, and developing smarter PDT platforms. Ultimately, these efforts aim to make PDT a first-choice treatment option for cancer patients.

Dysregulation of lipid metabolism in the liver of Tspo knockout mice

The translocator protein, TSPO, has been implicated in a wide range of cellular processes exerted from its position in the outer mitochondrial membrane from where it influences lipid metabolism and mitochondrial oxidative activity. Understanding how this protein regulates a profusion of processes requires further elucidation and to that end we have examined lipid metabolism and used an RNAseq strategy to compare transcript abundance in wildtype and Tspo knockout (KO) mouse liver. The levels of cholesterol, triglyceride and phospholipid were significantly elevated in the KO mouse liver. The expression of cholesterol homeostasis genes was markedly downregulated. Determination of the differential expression revealed that many genes were either up- or downregulated in the KO animals. However, a striking observation within the results was a decrease of transcripts for protein degradation proteins in KO animals while protease inhibitors were enriched. When the entire abundance data-set was analysed with CEMiTool, and revealed a module of proteins that were under-represented in the KO animals. These could subsequently be formed into a network comprising three interlinked clusters at the centre of which were proteins of cytoplasmic ribosomes with gene ontology terms suggesting impairment to translation. The largest cluster was dominated by proteins of lipid metabolism but also contained disparate systems of iron metabolism and behaviour. The third cluster was dominated by proteins of the electron transport chain and oxidative phosphorylation. These findings suggest that TSPO contributes to lipid metabolism, detoxification of active oxygen species and oxidative phosphorylation, and regulates mitochondrial retrograde signalling.

The mitochondrial TSPO ligand Atriol mitigates metabolic-associated steatohepatitis by downregulating CXCL1

BACKGROUND AND AIMS

The mitochondrial translocator protein (TSPO, 18 kDa) is pivotal in binding cholesterol and facilitating its transfer from the outer to the inner mitochondrial membrane. Atriol is a TSPO ligand disrupting cholesterol binding by targeting the cholesterol-recognition amino acid consensus domain. Prior research has shown that TSPO deficiency improved metabolic-associated steatohepatitis (MASH). We hypothesized that Atriol may have the potential to alleviate MASH.

METHODS AND RESULTS

In vitro cell culture studies revealed that Atriol treatment effectively mitigated MASH by restoring mitochondrial function, inhibiting the NF-κB signaling pathway, and reducing hepatic stellate cell (HSC) activation. SD male rats were fed a GAN diet for 10 months to induce MASH. During the final two weeks of feeding, rats received intraperitoneal Atriol administration daily. Atriol treatment significantly ameliorated MASH by reducing lipid accumulation, diminishing hepatic lobular inflammation and fibrosis, decreasing cell death, and inhibiting excessive bile acid synthesis. Moreover, Atriol restored mitochondrial function in primary hepatocytes isolated from MASH rats. In search of the mechanism(s) governing these effects, we found that Atriol downregulated the proinflammatory chemokine CXCL1 through the NF-κB signaling pathway or via myeloperoxidase (MPO) in HSCs and Kupffer cells. Additionally, in vitro, studies further suggested that CXCL1 treatment induced dysfunctional mitochondria, inflammation, HSCs activation, and macrophage migration, whereas Atriol countered these effects. Finally, the mitigating effects of Atriol on MASH were reproduced by pharmacological inhibition of NF-κB or MPO and neutralization of CXCL1.

CONCLUSION

Atriol ameliorates MASH both in vitro and in vivo, demonstrating its potential therapeutic benefits in managing MASH.