bims-mecosi 2024-04-14 papers

Issue of 2024–04–14
eight papers selected by
Verena Kohler, Umeå University

Contact (Thousand Oaks). 2024 Jan-Dec;7:7 25152564241244941

Contacting the gut: Mitochondria-associated Endoplasmic Reticulum Membranes in the Enteric Nervous System.

Jenny Greig, Giada Delfino, Pascal Derkinderen, Sébastien Paillusson.

Changes in the connections between the endoplasmic reticulum (ER) and mitochondria, as well as alterations in mitochondria-associated ER membrane (MAM) signalling, have been documented in various neurodegenerative diseases affecting the brain. Despite the growing recognition of the significance of the gut-brain axis in neurodegenerative conditions, there has been no prior investigation into the biology of MAM within the enteric nervous system (ENS). Our recent research reveals, for the first time, the existence of connections between the ER and mitochondria within enteric neurons. Additionally, we observed alterations in the dynamics of these connections in the enteric neurons from a mouse model exhibiting age-related neurodegeneration. These findings provide the first detailed characterization of MAM in the ENS under physiological conditions and in a mouse model of age-associated neurodegeneration and shed new light on the potential role of enteric MAM in the context of neurodegenerative disorders.

Keywords: Alzheimer's disease; Parkinson's disease; ageing; enteric nervous system; mitochondria-associated ER membranes

DOI: https://doi.org/10.1177/25152564241244941

bioRxiv. 2024 Mar 29. pii: 2024.03.25.586170. [Epub ahead of print]

MITOCHONDRIA-ASSOCIATED MEMBRANES ARE NOT ALTERED IN IMMUNE CELLS IN T2D.

Samantha N Hart, Raji Lenin, Jamie Sturgill, Philip A Kern, Barbara Nikolajczyk.

Metabolism research is increasingly recognizing the contributions of organelle crosstalk to metabolic regulation. Mitochondria-associated membranes (MAMs), which are structures connecting the mitochondria and endoplasmic reticulum (ER), are critical in a myriad of cellular functions linked to cellular metabolism. MAMs control calcium signaling, mitochondrial transport, redox balance, protein folding/degradation, and in some studies, metabolic health. The possibility that MAMs drive changes in cellular function in individuals with Type 2 Diabetes (T2D) is controversial. Although disruptions in MAMs that change the distance between the mitochondria and ER, MAM protein composition, or disrupt downstream signaling, can perpetuate inflammation, one key trait of T2D. However, the full scope of this structure's role in immune cell health and thus T2D-associated inflammation remains unknown. We show that human immune cell MAM proteins and their associated functions are not altered by T2D and thus unlikely to contribute to metaflammation.

DOI: https://doi.org/10.1101/2024.03.25.586170

CNS Neurosci Ther. 2024 Apr;30(4): e14707

Mitochondria-associated endoplasmic reticulum membranes tethering protein VAPB-PTPIP51 protects against ischemic stroke through inhibiting the activation of autophagy.

Mingyang Li, Yonggang Zhang, Guixiang Yu, Lijuan Gu, Hua Zhu, Shi Feng, Xiaoxing Xiong, Zhihong Jian.

AIMS: Mitochondria-associated endoplasmic reticulum membranes (MAMs) serve as a crucial bridge connecting the endoplasmic reticulum (ER) and mitochondria within cells. Vesicle-associated membrane protein-associated protein B (VAPB) and protein tyrosine phosphatase interacting protein 51 (PTPIP51) are responsible for the formation and stability of MAMs, which have been implicated in the pathogenesis of various diseases. However, the role of MAMs in ischemic stroke (IS) remains unclear. We aimed to investigate the role of MAMs tethering protein VAPB-PTPIP51 in experimental cerebral ischemia.
METHODS: We simulated cerebral ischemia-reperfusion injury (CIRI) by using a mouse middle cerebral artery occlusion (MCAO) model.
RESULTS: We observed a decrease in VAPB-PTPIP51 expression in the brain tissue. Our findings suggested compromised MAMs after MCAO, as a decreased mitochondria-ER contact (MERC) coverage and an increased distance were observed through the transmission electron microscope (TEM). Upon VAPB or PTPIP51 knockdown, the damage to MAMs was exacerbated, accompanied by excessive autophagy activation and increased reactive oxygen species (ROS) production, resulting in an enlarged infarct area and exacerbated neurological deficits. Notably, we observed that this damage was concomitant with the inhibition of the PI3K/AKT/mTOR pathway and was successfully mitigated by the treatment with the PI3K activator.
CONCLUSIONS: Our findings suggest that the downregulation of VAPB-PTPIP51 expression after IS mediates structural damage to MAMs. This may exacerbate CIRI by inhibiting the PI3K pathway and activating autophagy, thus providing new therapeutic targets for IS.

Keywords: MAMs; PI3K/AKT/mTOR; VAPB‐PTPIP51; autophagy; ischemic stroke

DOI: https://doi.org/10.1111/cns.14707

Cells. 2024 Apr 07. pii: 647. [Epub ahead of print]13(7):

Miro GTPases at the Crossroads of Cytoskeletal Dynamics and Mitochondrial Trafficking.

Pontus Aspenström.

Miro GTPases are key components in the machinery responsible for transporting mitochondria and peroxisomes along microtubules, and also play important roles in regulating calcium homeostasis and organizing contact sites between mitochondria and the endoplasmic reticulum. Moreover, Miro GTPases have been shown to interact with proteins that actively regulate cytoskeletal organization and dynamics, suggesting that these GTPases participate in organizing cytoskeletal functions and organelle transport. Derailed mitochondrial transport is associated with neuropathological conditions such as Parkinson's and Alzheimer's diseases. This review explores our recent understanding of the diverse roles of Miro GTPases under cytoskeletal control, both under normal conditions and during the course of human diseases such as neuropathological disorders.

Keywords: Miro GTPases; Parkinson’s disease; microtubules; mitochondrial dynamics; neuropathology

DOI: https://doi.org/10.3390/cells13070647

Aging Dis. 2024 Mar 18.

C. elegans Presenilin Mediates Inter-Organelle Contacts and Communication that Is Required for Lysosome Activity.

Kerry C Ryan, Zahra Ashkavand, Jocelyn T Laboy, Ling Wang, Margarida Barroso, Kenneth R Norman.

Compromised lysosome function is implicated in the pathology of many neurodegenerative diseases, including Alzheimer's disease (AD). Familial Alzheimer's disease (fAD) is caused primarily by mutations in the presenilin encoding genes, but the underlying mechanism remains obscure. Loss of the conserved C. elegans presenilin orthologue SEL-12 results in increased mitochondrial calcium, which promotes neurodegeneration. Here, we find that sel-12 mutant lysosomes, independent of SEL-12 proteolytic activity, are significantly enlarged and more alkaline due to increased ER-to-mitochondrial calcium signaling and concomitant mitochondrial oxidative stress. These defects and their dependence on mitochondrial calcium are recapitulated in human fAD fibroblasts, demonstrating a conserved role for mitochondrial calcium in presenilin-mediated lysosome dysfunction. sel-12 mutants also have increased contact surface area between the ER, mitochondria, and lysosomes, suggesting sel-12 has an additional role in modulating organelle contact and communication. Overall, we demonstrate that SEL-12 maintains lysosome acidity and lysosome health by controlling ER-to-mitochondrial calcium signaling.

DOI: https://doi.org/10.14336/AD.2024.0228

J Diabetes. 2024 Apr;16(4): e13540

Mitochondria-associated membranes contribution to exercise-mediated alleviation of hepatic insulin resistance: Contrasting high-intensity interval training with moderate-intensity continuous training in a high-fat diet mouse model.

Xi Li, Jun Yang Yang, Wen Zhi Hu, YuXin Ruan, Hong Ying Chen, Qiang Zhang, Zhe Zhang, Zhe Shu Ding.

OBJECTIVE: Mitochondria-associated membranes (MAMs) serve pivotal functions in hepatic insulin resistance (IR). Our aim was to explore the potential role of MAMs in mitigating hepatic IR through exercise and to compare the effects of different intensities of exercise on hepatic MAMs formation in high-fat diet (HFD) mice.
METHODS: Male C57BL/6J mice were fed an HFD and randomly assigned to undergo supervised high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT). IR was evaluated using the serum triglyceride/high-density lipoprotein cholesterol ratio (TG/HDL-C), glucose tolerance test (GTT), and insulin tolerance test (ITT). Hepatic steatosis was observed using hematoxylin-eosin (H&E) and oil red O staining. The phosphatidylinositol 3-kinase/protein kinase B/glycogen synthase kinase 3 beta (PI3K-AKT-GSK3β) signaling pathway was assessed to determine hepatic IR. MAMs were evaluated through immunofluorescence (colocalization of voltage-dependent anion-selective channel 1 [VDAC1] and inositol 1,4,5-triphosphate receptor [IP3R]).
RESULTS: After 8 weeks on an HFD, there was notable inhibition of the hepatic PI3K/Akt/GSK3β signaling pathway, accompanied by a marked reduction in hepatic IP3R-VDAC1 colocalization levels. Both 8-week HIIT and MICT significantly enhanced the hepatic PI3K/Akt/GSK3β signaling and colocalization levels of IP3R-VDAC1 in HFD mice, with MICT exhibiting a stronger effect on hepatic MAMs formation. Furthermore, the colocalization of hepatic IP3R-VDAC1 positively correlated with the expression levels of phosphorylation of protein kinase B (p-AKT) and phosphorylation of glycogen synthase kinase 3 beta (p-GSK3β), while displaying a negative correlation with serum triglyceride/high-density lipoprotein cholesterol levels.
CONCLUSION: The reduction in hepatic MAMs formation induced by HFD correlates with the development of hepatic IR. Both HIIT and MICT effectively bolster hepatic MAMs formation in HFD mice, with MICT demonstrating superior efficacy. Thus, MAMs might wield a pivotal role in exercise-induced alleviation of hepatic IR.

Keywords: exercise; hepatic insulin resistance; high‐intensity interval training; mitochondria‐associated membrane; moderate‐intensity continuous training

DOI: https://doi.org/10.1111/1753-0407.13540

FEBS Lett. 2024 Apr 11.

The lipid droplet lipidome.

Michele Wölk, Maria Fedorova.

Lipid droplets (LDs) are intracellular organelles with a hydrophobic core formed by neutral lipids surrounded by a phospholipid monolayer harboring a variety of regulatory and enzymatically active proteins. Over the last few decades, our understanding of LD biology has evolved significantly. Nowadays, LDs are appreciated not just as passive energy storage units, but rather as active players in the regulation of lipid metabolism and quality control machineries. To fulfill their functions in controlling cellular metabolic states, LDs need to be highly dynamic and responsive organelles. A large body of evidence supports a dynamic nature of the LD proteome and its contact sites with other organelles. However, much less is known about the lipidome of LDs. Numerous examples clearly indicate the intrinsic link between LD lipids and proteins, calling for a deeper characterization of the LD lipidome in various physiological and pathological settings. Here, we reviewed the current state of knowledge in the field of the LD lipidome, providing a brief overview of the lipid classes and their molecular species present within the neutral core and phospholipid monolayer.

Keywords: lipid droplets; lipid molecular species; lipidome; neutral core; phospholipid monolayer

DOI: https://doi.org/10.1002/1873-3468.14874