bims-mecosi 2022-08-21 papers

Issue of 2022–08–21
five papers selected by
Verena Kohler, Stockholm University

J Cell Biol. 2022 Sep 05. pii: e202112107. [Epub ahead of print]221(9):

ORP5 and ORP8 orchestrate lipid droplet biogenesis and maintenance at ER-mitochondria contact sites.

Valentin Guyard, Vera Filipa Monteiro-Cardoso, Mohyeddine Omrane, Cécile Sauvanet, Audrey Houcine, Claire Boulogne, Kalthoum Ben Mbarek, Nicolas Vitale, Orestis Faklaris, Naima El Khallouki, Abdou Rachid Thiam, Francesca Giordano.

Lipid droplets (LDs) are the primary organelles of lipid storage, buffering energy fluctuations of the cell. They store neutral lipids in their core that is surrounded by a protein-decorated phospholipid monolayer. LDs arise from the endoplasmic reticulum (ER). The ER protein seipin, localizing at ER-LD junctions, controls LD nucleation and growth. However, how LD biogenesis is spatially and temporally coordinated remains elusive. Here, we show that the lipid transfer proteins ORP5 and ORP8 control LD biogenesis at mitochondria-associated ER membrane (MAM) subdomains, enriched in phosphatidic acid. We found that ORP5/8 regulates seipin recruitment to these MAM-LD contacts, and their loss impairs LD biogenesis. Importantly, the integrity of ER-mitochondria contact sites is crucial for ORP5/8 function in regulating seipin-mediated LD biogenesis. Our study uncovers an unprecedented ORP5/8 role in orchestrating LD biogenesis and maturation at MAMs and brings novel insights into the metabolic crosstalk between mitochondria, ER, and LDs at the membrane contact sites.

DOI: https://doi.org/10.1083/jcb.202112107

Microb Cell. 2022 Aug 01. 9(8): 145-157

Up-regulation of Osh6 boosts an anti-aging membrane trafficking pathway toward vacuoles.

Ilham Kadhim, Nazneen Begum, William King, Licheng Xu, Fusheng Tang.

Members of the family of oxysterol-binding proteins mediate non-vesicular lipid transport between membranes and contribute to longevity in different manners. We previously found that a 2-fold up-regulation of Osh6, one of seven yeast oxysterol-binding proteins, remedies vacuolar morphology defects in mid-aged cells, partly down-regulates the target of rapamycin complex 1 (TORC1), and increases the replicative lifespan. At the molecular level, Osh6 transports phosphatidylserine (PS) and phosphatidylinositol-4-phosphate (PI4P) between the endoplasmic reticulum (ER) and the plasma membrane (PM). To decipher how an ER-PM working protein controls vacuolar morphology, we tested genetic interactions between OSH6 and DRS2, whose protein flips PS from the lumen to the cytosolic side of the Golgi, the organelle between ER and vacuoles in many pathways. Up-regulated OSH6 complemented vacuolar morphology of drs2Δ and enriched PI4P on the Golgi, indicating that Osh6 also works on the Golgi. This altered PI4P-enrichment led to a delay in the secretion of the proton ATPase Pma1 to the PM and a rerouting of Pma1 to vacuoles in a manner dependent on the trans-Golgi network (TGN) to late endosome (LE) trafficking pathway. Since the TGN-LE pathway controls endosomal and vacuolar TORC1, it may be the anti-aging pathway boosted by up-regulated Osh6.

Keywords: Golgi; Osh6; PI4P; longevity; vacuole

DOI: https://doi.org/10.15698/mic2022.08.783

Geroscience. 2022 Aug 18.

Microbiota mitochondria disorders as hubs for early age-related macular degeneration.

János Fehér, Ágnes Élő, Lilla István, Zoltán Zsolt Nagy, Zsolt Radák, Gianluca Scuderi, Marco Artico, Illés Kovács.

Age-related macular degeneration (AMD) is a progressive neurodegenerative disease affecting the central area (macula lutea) of the retina. Research on the pathogenic mechanism of AMD showed complex cellular contribution governed by such risk factors as aging, genetic predisposition, diet, and lifestyle. Recent studies suggested that microbiota is a transducer and a modifier of risk factors for neurodegenerative diseases, and mitochondria may be one of the intracellular targets of microbial signaling molecules. This review explores studies supporting a new concept on the contribution of microbiota-mitochondria disorders to AMD. We discuss metabolic, vascular, immune, and neuronal mechanism in AMD as well as key alterations of photoreceptor cells, retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris endothelial, immune, and neuronal cells. Special attention was paid to alterations of mitochondria contact sites (MCSs), an organelle network of mitochondria, endoplasmic reticulum, lipid droplets (LDs), and peroxisomes being documented based on our own electron microscopic findings from surgically removed human eyes. Morphometry of Bruch's membrane lipids and proteoglycans has also been performed in early AMD and aged controls. Microbial metabolites (short-chain fatty acids, polyphenols, and secondary bile acids) and microbial compounds (lipopolysaccharide, peptidoglycan, and bacterial DNA)-now called postbiotics-in addition to local effects on resident microbiota and mucous membrane, regulate systemic metabolic, vascular, immune, and neuronal mechanisms in normal conditions and in various common diseases. We also discuss their antioxidant, anti-inflammatory, and metabolic effects as well as experimental and clinical observations on regulating the main processes of photoreceptor renewal, mitophagy, and autophagy in early AMD. These findings support an emerging concept that microbiota-mitochondria disorders may be a crucial pathogenic mechanism of early AMD; and similarly, to other age-related neurodegenerative diseases, new treatment approaches should be targeted at these disorders.

Keywords: Age-related macular degeneration; Bruch’s membrane; Choriocapillaris; Electron microscopy; Ferroptosis; Innate immunity; Lipid droplets; Microbiota; Microglia; Mitochondria; Mitochondria contact sites; Morphometry; Photoreceptor; Retinal pigment epithelium

DOI: https://doi.org/10.1007/s11357-022-00620-5

Mol Biol (Mosk). 2022 Jul-Aug;56(4):56(4): 564-573

[The GTP-Bound form of Rab3D Promotes Lipid Droplet Growth in Adipocyte].

T Wang, M J Jin, L K Li.

Rab GTPases are major regulators of membrane trafficking. Proteome profiling reveals dozens of Rab proteins associated with lipid droplets (LDs), but few of them have been functionally validated. Cell death activator CIDE-3 protein mediates LD fusion and growth. It is highly enriched at LD-LD contact sites. Here, we investigated the role of Rab3D in lipid storage in adipocyte. We verified that the adipose levels of Rab3D transcript were higher than that of other Rab3 family members; the differences were most pronounced in white adipose tissue. Moreover, we showed that Rab3D promotes LD growth in 3T3-L1 preadipocytes in a dose dependent manner, independently of the process of CIDE-3-mediated LD fusion. Finally, we confirmed that the GTP-bound form of Rab3D is its LD promoting form; it translocates from other vesicles to LDs during adipocyte differentiation. By contrast, the Rab3D-GDP form is retained in the cytoplasm and has no effect on LD sizes. Presented results provide evidence for the role of Rab3D in controlling formation of large LDs in adipocytes. We conclude that Rab3D is a novel LD regulator with characteristics differing from these of previously identified LD associated Rab proteins, such as Rab18 and Rab8a.

Keywords: Rab3D; adipocyte; lipid droplet

DOI: https://doi.org/10.31857/S0026898422040140

J Biomed Sci. 2022 Aug 18. 29(1): 61

The A'-helix of CYP11A1 remodels mitochondrial cristae.

Karen G Rosal, Wei-Yi Chen, Bon-Chu Chung.

BACKGROUND: CYP11A1 is a protein located in the inner membrane of mitochondria catalyzing the first step of steroid synthesis. As a marker gene for steroid-producing cells, the abundance of CYP11A1 characterizes the extent of steroidogenic cell differentiation. Besides, the mitochondria of fully differentiated steroidogenic cells are specialized with tubulovesicular cristae. The participation of CYP11A1 in the change of mitochondrial structure and the differentiation of steroid-producing cells, however, has not been investigated.
METHODS: We engineered nonsteroidogenic monkey kidney COS1 cells to express CYP11A1 upon doxycycline induction and examined the mitochondrial structure of these cells. We also mapped the CYP11A1 domains that confer structural changes of mitochondria. We searched for CYP11A1-interacting proteins and investigated the role of this interacting protein in shaping mitochondrial structure. Finally, we examined the effect of CYP11A1 overexpression on the amount of mitochondrial contact site and cristae organizing system.
RESULTS: We found that CYP11A1 overexpression led to the formation of tubulovesicular cristae in mitochondria. We also identified the A'-helix located at amino acid #57-68 to be sufficient for membrane insertion and crista remodeling. We identified heat shock protein 60 (Hsp60) as the CYP11A1-interacting protein and showed that Hsp60 is required for CYP11A1 accumulation and crista remodeling. Finally, we found that the small MIC10 subcomplex of the mitochondrial contact site and cristae organizing system was reduced when CYP11A1 was overexpressed.
CONCLUSIONS: CYP11A1 participates in the formation of tubulovesicular cristae in the mitochondria of steroidogenic cells. Its A'-helix is sufficient for the formation of tubulovesicular cristae and for protein integration into the membrane. CYP11A1 interacts with Hsp60, which is required for CYP11A1 accumulation. The accumulation of CYP11A1 leads to the reduction of MIC10 complex and changes mitochondrial structure.

Keywords: Cristae remodeling; Hsp60; MIC10; Membrane; Mitochondrial structure; P450scc; Pregnenolone; Steroidogenesis

DOI: https://doi.org/10.1186/s12929-022-00846-7