bims-mecosi 2024-09-29 papers

Issue of 2024–09–29
five papers selected by
Verena Kohler, Umeå University

EMBO Rep. 2024 Sep 27.

A novel bacterial effector protein mediates ER-LD membrane contacts to regulate host lipid droplets.

Rajendra Kumar Angara, Arif Sadi, Stacey D Gilk.

Effective intracellular communication between cellular organelles occurs at dedicated membrane contact sites (MCSs). Tether proteins are responsible for the establishment of MCSs, enabling direct communication between organelles to ensure organelle function and host cell homeostasis. While recent research has identified tether proteins in several bacterial pathogens, their functions have predominantly been associated with mediating inter-organelle communication between the bacteria containing vacuole (BCV) and the host endoplasmic reticulum (ER). Here, we identify a novel bacterial effector protein, CbEPF1, which acts as a molecular tether beyond the confines of the BCV and facilitates interactions between host cell organelles. Coxiella burnetii, an obligate intracellular bacterial pathogen, encodes the FFAT motif-containing protein CbEPF1 which localizes to host lipid droplets (LDs). CbEPF1 establishes inter-organelle contact sites between host LDs and the ER through its interactions with VAP family proteins. Intriguingly, CbEPF1 modulates growth of host LDs in a FFAT motif-dependent manner. These findings highlight the potential for bacterial effector proteins to impact host cellular homeostasis by manipulating inter-organelle communication beyond conventional BCVs.

Keywords: Coxiella burnetii ; FFAT Motif; Inter-organelle Contacts; Lipid Droplets; Molecular Tethers

DOI: https://doi.org/10.1038/s44319-024-00266-8

Exp Eye Res. 2024 Sep 24. pii: S0014-4835(24)00332-4. [Epub ahead of print] 110110

Current Insights on Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs) and their significance in the pathophysiology of ocular disorders.

Xin-Yu Zhang, Cheng Han, Yong Yao, Ting-Ting Wei.

The intricate interaction network necessary for essential physiological functions underscores the interdependence among eukaryotic cells. Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs), specialized junctions between mitochondria and the ER, were recently discovered. These junctions participate in various cellular processes, including calcium level regulation, lipid metabolism, mitochondrial integrity maintenance, autophagy, and inflammatory responses via modulating the structure and molecular composition of various cellular components. Therefore, MAMs contribute to the pathophysiology of numerous ocular disorders, including Diabetic Retinopathy (DR), Age-related Macular Degeneration (AMD) and glaucoma. In addition to providing a concise overview of the architectural and functional aspects of MAMs, this review explores the key pathogenetic pathways involving MAMs in the development of several ocular disorders.

Keywords: Eye Diseases; Mitochondria-Associated Endoplasmic Reticulum Membranes; Pathophysiology

DOI: https://doi.org/10.1016/j.exer.2024.110110

Toxicology. 2024 Sep 20. pii: S0300-483X(24)00237-3. [Epub ahead of print]509 153956

Di-(2-ethylhexyl) phthalate induces prepubertal testicular injury through MAM-related mitochondrial calcium overload in Leydig and Sertoli cell apoptosis.

Junke Wang, Yuexin Wei, Yuhao Wu, Tianxin Zhao, Lian Kang, Lindong Han, Jiadong Chen, Chunlan Long, Guanghui Wei, Lianju Shen, Shengde Wu.

As one of the most prevalent environmental endocrine disruptors, di-(2-ethylhexyl) phthalate (DEHP) is known for its significant developmental toxicity to the male reproductive system in humans and mice. Prepubertal exposure to DEHP has been shown to cause testicular damage, but the underlying mechanisms require further investigation. To investigate this effect, prepubertal mice were exposed to 100, 250 or 500 mg/kg body weight (bw) of DEHP for 14 days, which resulted in impaired histological structure and increased apoptosis of the testes. RNA sequencing (RNA-seq) of testicular tissue suggested that DEHP led to injury in Leydig and Sertoli cells. To further elucidate these mechanisms, we conducted experiments using immature mouse Leydig (TM3) and Sertoli (TM4) cells, and exposed them to 200 μM mono-(2-ethylhexyl) phthalate (MEHP), the primary metabolite of DEHP, for 24 h. We found that MEHP exposure induced oxidative stress injury and promoted cell apoptosis, and that cotreatment with N-acetylcysteine partially reversed these injuries. Given the close association between oxidative stress and mitochondrial calcium levels, we demonstrated that MEHP exposure disrupted mitochondria and increased mitochondrial calcium levels. In addition, MEHP exposure facilitated the formation of mitochondria-associated endoplasmic reticulum membranes (MAMs), upregulated protein expression and enhanced the interactions of the IP3R3-Grp75-VDAC1 complex. Furthermore, inhibition of calcium transfer in the IP3R3-Grp75-VDAC1-MCU axis relieved MEHP-induced mitochondrial injury, oxidative stress and apoptosis in TM3 and TM4 cells. This study highlights the importance of MAM-mediated mitochondrial calcium overload and the subsequent apoptosis of Leydig and Sertoli cells as pivotal factors contributing to testicular injury induced by prepubertal exposure to DEHP.

Keywords: DEHP; Mitochondria-associated endoplasmic reticulum membranes; Mitochondrial injury; Oxidative stress; Prepubertal testis

DOI: https://doi.org/10.1016/j.tox.2024.153956

J Ethnopharmacol. 2024 Sep 25. pii: S0378-8741(24)01155-3. [Epub ahead of print] 118856

Mitigation of lipopolysaccharide-induced intestinal injury in rats by Chimonanthus nitens Oliv. essential oil via suppression of mitochondrial fusion protein mitofusin 2 (MFN2)-mediated mitochondrial-associated endoplasmic reticulum membranes (MAMs) formation.

Shuying Huang, Zhenguo Zeng, Yuelei Chu, Shichao Zhang, Jia Zhou, Zhiguo Hu, Yuting Yang, Chaoqi Zhou, Wang Cheng, Songyu Yang, Shengbin Chen, Wenjuan Li, Cheng Qing.

ETHNOPHARMACOLOGICAL RELEVANCE: Chimonanthus nitens Oliv. is a traditional Chinese medicine with anti-inflammatory and antioxidant properties that has commonly been used for colds, fevers, and other diseases. However, its role and specific mechanism in sepsis-associated intestinal injury have not been reported.
AIM OF THE STUDY: C. nitens Oliv. essential oil (CEO), an organic active compound extracted from the traditional Chinese medicine C. nitens Oliv. exhibits notable anti-inflammatory and antioxidant properties. Nevertheless, the therapeutic potential of CEO for septic intestinal injury remains undocumented. This study thus aims to elucidate the anti-inflammatory and antioxidant effects of CEO in the context of acute intestinal injury and to investigate its mechanisms of action in septic rats.
MATERIALS AND METHODS: Cell and animal models were established using LPS to investigate the impact of CEO on LPS-induced intestinal pathological injury and the secretion of inflammatory factor IL-1β. The effects of CEO on the expression of NLRP3, caspase-1, and MFN2, p-p65 protein were also examined, as well as its influence on oxidative stress injury and mitochondrial-associated endoplasmic reticulum membrane (MAM) formation. Generation of an MFN2 knockout IEC-6 cell line allowed comprehensive investigation of the protective mechanism of CEO.
RESULTS: In rat models, CEO reduced IL-1β secretion, inhibited caspase-1, ZO-1 expression and NF-κB p65 phosphorylation, while also decreasing malondialdehyde levels and enhancing superoxide dismutase activity in intestinal tissues. Cellular experiments demonstrated its ability to decrease IL-1β secretion; NLRP3, caspase-1, and MFN2 expression; NF-κB p65 phosphorylation; reactive oxygen species (ROS) production, and mitochondrial dysfunction. MFN2 knockdown enhanced these effects synergistically with CEO, indicating potential therapeutic synergy. Further, MFN2 knockdown significantly mitigated LPS-induced NLRP3 and caspase-1 expression, IL-1β secretion, ROS production, NF-κB p65 phosphorylation and MMP reduction in IEC-6 cells, while inhibiting MAM formation and NLRP3 localization on MAMs. Importantly, MFN2 downregulation and CEO synergistically reduced LPS-induced IL-1β secretion and ROS production while inhibiting MAM formation in IEC-6 cells, thus inhibiting NLRP3 inflammasome activation.
CONCLUSION: CEO mitigates inflammation and oxidative stress by inhibiting MAM formation and is thus a promising intervention for septic intestinal injury.

Keywords: Chimonanthus nitens Oliv. essential oil; Mitochondria-associated endoplasmic reticulum membranes (MAMs); NLRP3 inflammasome; Oxidative Stress; Septic intestinal injury

DOI: https://doi.org/10.1016/j.jep.2024.118856

Int Immunopharmacol. 2024 Sep 26. pii: S1567-5769(24)01721-1. [Epub ahead of print]142(Pt B): 113199

NPLOC4 aggravates heart failure by regulating ROS and mitochondrial function.

Kaidi Ren, Yi Luan, Yuanyuan Sun, Siyuan Huang, Shuwei Zhang, Yang Yang, Yage Jin, Xing Chen.

Heart failure (HF) is a leading cause of morbidity and mortality worldwide, necessitating the discovery of new therapeutic targets. NPLOC4 is known as an endoplasmic reticulum protein involved in protein degradation and cellular stress responses. Herein, NPLOC4 was investigated for its role in HF using a transverse aortic constriction (TAC) mouse model and an Angiotensin II (Ang II)-induced H9c2 cardiomyocyte model. Transcriptomic analysis revealed NPLOC4 upregulation in HF. NPLOC4 knockdown in the TAC model inhibited HF progression, as evidenced by reduced cardiac hypertrophy and fibrosis. Subsequent knockdown experiments showed the relievement in heart failure phenotypes, reduced reactive oxygen species (ROS) levels and enhanced mitochondrial function caused by NPLOC4 depletion in Ang II-induced H9c2 cells. STRING analysis predicted ERO1α as a potential NPLOC4 interactor, with further studies identifying that NPLOC4 knockdown increases ERO1α expression and disrupts mitochondria-associated membranes (MAMs). Additionally, NPLOC4 knockdown modulated the β-catenin/GSK3β pathway, enhancing mitochondrial dynamics and mitophagy. These findings suggest NPLOC4 as a promising therapeutic target for HF.

Keywords: ERO1α; Heart failure; Mitochondrial function; NPLOC4; β-catenin/GSK3β pathway

DOI: https://doi.org/10.1016/j.intimp.2024.113199