bims-mecosi 2022-02-06 papers

Issue of 2022–02–06
five papers selected by
Verena Kohler, Stockholm University

Front Cell Dev Biol. 2021 ;9 788634

FUNDC1: A Promising Mitophagy Regulator at the Mitochondria-Associated Membrane for Cardiovascular Diseases.

Guoyong Li, Junli Li, Ruochen Shao, Jiahao Zhao, Mao Chen.

Mitochondrial autophagy (or mitophagy) regulates the mitochondrial network and function to contribute to multiple cellular processes. The protective effect of homeostatic mitophagy in cardiovascular diseases (CVDs) has attracted increasing attention. FUN14 domain containing 1 (FUNDC1), an identified mitophagy receptor, plays an essential role in CVDs. Different expression levels of FUNDC1 and its phosphorylated state at different sites alleviate or exacerbate hypoxia and ischemia/reperfusion injury, cardiac hypertrophy, or metabolic damage through promotion or inhibition of mitophagy. In addition, FUNDC1 can be enriched at contact sites between mitochondria and the endoplasmic reticulum (ER), determining the formation of mitochondria-associated membranes (MAMs) that regulate cellular calcium (Ca2+) homeostasis and mitochondrial dynamics to prevent heart dysfunction. Moreover, FUNDC1 has also been involved in inflammatory cardiac diseases such as septic cardiomyopathy. In this review, we collect and summarize the evidence on the roles of FUNDC1 exclusively in various CVDs, describing its interactions with different cellular organelles, its involvement in multiple cellular processes, and its associated signaling pathways. FUNDC1 may become a promising therapeutic target for the prevention and management of various CVDs.

Keywords: FUNDC1; LC3; MAM; cardiovascular diseases; mitophagy

DOI: https://doi.org/10.3389/fcell.2021.788634

Proc Natl Acad Sci U S A. 2022 Feb 08. pii: e2117554119. [Epub ahead of print]119(6):

ER-phagy requires the assembly of actin at sites of contact between the cortical ER and endocytic pits.

Dongmei Liu, Muriel Mari, Xia Li, Fulvio Reggiori, Susan Ferro-Novick, Peter Novick.

Fragments of the endoplasmic reticulum (ER) are selectively delivered to the lysosome (mammals) or vacuole (yeast) in response to starvation or the accumulation of misfolded proteins through an autophagic process known as ER-phagy. A screen of the Saccharomyces cerevisiae deletion library identified end3Δ as a candidate knockout strain that is defective in ER-phagy during starvation conditions, but not bulk autophagy. We find that loss of End3 and its stable binding partner Pan1, or inhibition of the Arp2/3 complex that is coupled by the End3-Pan1 complex to endocytic pits, blocks the association of the cortical ER autophagy receptor, Atg40, with the autophagosomal assembly scaffold protein Atg11. The membrane contact site module linking the rim of cortical ER sheets and endocytic pits, consisting of Scs2 or Scs22, Osh2 or Osh3, and Myo3 or Myo5, is also needed for ER-phagy. Both Atg40 and Scs2 are concentrated at the edges of ER sheets and can be cross-linked to each other. Our results are consistent with a model in which actin assembly at sites of contact between the cortical ER and endocytic pits contributes to ER sequestration into autophagosomes.

Keywords: actin; autophagy; endoplasmic reticulum

DOI: https://doi.org/10.1073/pnas.2117554119

STAR Protoc. 2022 Mar 18. 3(1): 101119

Fluorescence imaging detection of nanodomain redox signaling events at organellar contacts.

David M Booth, Péter Várnai, Suresh K Joseph, György Hajnóczky.

This protocol describes how to visualize, detect, and analyze redox signals (oxidative bursts) at the ER-mitochondrial interface. It uses drug-inducible crosslinking to target the genetically encoded glutathione redox sensor Grx1roGFP2 to organellar contact sites to measure local redox changes associated with transient depolarizations of the mitochondrial membrane potential (flickers). The strategy allows imaging of the oxidized to reduced glutathione ratio (GSSG:GSH) in subcellular regions below the diffraction limit with good temporal resolution and minimum phototoxicity. Moreover, the strategy also applies to diverse parameters including pH, H2O2, and Ca2+. For complete details on the use and execution of this profile, please refer to Booth et al. (2016) and Booth et al. (2021).

Keywords: Cell Biology; Microscopy; Molecular/Chemical Probes

DOI: https://doi.org/10.1016/j.xpro.2021.101119

Alzheimers Dement. 2021 Dec;17 Suppl 3 e051164

Lipidome changes due to accumulation of cholesterol via APP-C99 alters neuronal permeability.

Jorge Montesinos, Estela Area-Gomez.

BACKGROUND: γ-secretase activity is enriched at mitochondria-associated ER membranes (MAMs),a lipid-raft subdomain of the ER, where APP fragment C99 is delivered for its cleavage. Moreover, γ-secretase activity deficiency linked to AD mutations causes C99 accumulation at MAM, resulting in the upregulation of MAM activities such as sphingomyelin turnover and cholesterol esterification. We now explore whether the interaction of C99 with cholesterol could explain the link between C99 accumulation at MAM and the lipid abnormalities found in AD.
METHOD: Using cellular models of C99 accumulation versus a cholesterol-binding deficient C99, we assessed cholesterol uptake dynamics and sub-cellular distribution along with MAM-regulated functionalities. Also, we used a photo click activable cholesterol analog to study the proteins interacting with cholesterol at MAM in both conditions. Finally, we compare membrane permeability dynamics in neuronal models of Alzheimer's disease.
RESULT: C99 accumulation at MAM caused an increase in cholesterol uptake, cholesterol esterification, phospholipid synthesis and sphingomyelinase activity accompanied by a sub cellular redistribution of cholesterol to endolysosomes and ER, while C99-defective in cholesterol binding showed no changes in these activities. Moreover, when the cholesterol-interacting proteome of both conditions was compared, C99 caused a huge change/recruitment at MAM, especially of enzymes involved in lipid metabolism. ACSL4 (Acyl-CoA Synthetase Long Chain Family Member 4) activation was detected as an important player in the lipidome changes associated with C99 accumulation that led to membrane permeability alterations CONCLUSION: We report that the lipid alterations caused by pathogenic C99 accumulation are a consequence of an exacerbated uptake of extracellular cholesterol and mobilization towards MAM. The increase content of cholesterol at MAM driven by C99 might be responsible of the persistent activation of MAM and a subsequent alteration of the lipid metabolism since a cholesterol-binding deficient C99 fails to increase MAM activities and cholesterol trafficking. We also point to ACSL4 activation as a possible molecular switch for the permeability changes found in cellular models of AD.

DOI: https://doi.org/10.1002/alz.051164

Front Cardiovasc Med. 2021 ;8 790612

IL-6/STAT3 Signaling Promotes Cardiac Dysfunction by Upregulating FUNDC1-Dependent Mitochondria-Associated Endoplasmic Reticulum Membranes Formation in Sepsis Mice.

Tao Jiang, Dewei Peng, Wei Shi, Junyi Guo, Shengqi Huo, Lintong Men, Cuntai Zhang, Sheng Li, Jiagao Lv, Li Lin.

Aims: Cytokine storm is closely related to the initiation and progression of sepsis, and the level of IL-6 is positively correlated with mortality and organ dysfunction. Sepsis-induced myocardial dysfunction (SIMD) is one of the major complications. However, the role of the IL-6/STAT3 signaling in the SIMD remains unclear.
Methods and Results: Septic mice were induced by intraperitoneal injection of LPS (10 mg/kg). Echocardiography, cytokines detection, and histologic examination showed that sepsis mice developed cardiac systolic and diastolic dysfunction, increase of inflammatory cytokines in serum, activated STAT3 and TLR4/NFκB pathway in heart, and raised myocardial apoptosis, which were attenuated by IL-6/STAT3 inhibitor, Bazedoxifene. In vitro, we found that LPS decreased cell viability in a concentration-dependent manner and activated STAT3. Western blot and immunofluorescence results indicated that STAT3 phosphorylation induced by LPS was inhibited by Bazedoxifene. Bazedoxifene also suppressed LPS-induced IL-6 transcription. sIL-6R caused LPS-induced p-STAT3 firstly decreased and then significantly increased. More importantly, we found STAT3-knockdown suppressed LPS-induced expression of FUNDC1, a protein located in mitochondria-associated endoplasmic reticulum membranes (MAMs). Overexpression of STAT3 led to an increase in FUNDC1 expression. Dual-luciferase reporter assay was used to confirm that STAT3 was a potential transcription factor for FUNDC1. Moreover, we showed that LPS increased MAMs formation and intracellular Ca2+ levels, enhanced the expression of Cav1.2 and RyR2, decreased mitochondrial membrane potential and intracellular ATP levels, and promoted mitochondrial fragmentation, the expression of mitophagy proteins and ROS production in H9c2 cells, which were reversed by knockdown of FUNDC1 and IL-6/STAT3 inhibitor including Bazedoxifene and Stattic.
Conclusions: IL-6/STAT3 pathway plays a key role in LPS-induced myocardial dysfunction, through regulating the FUNDC1-associated MAMs formation and interfering the function of ER and mitochondria. IL-6/STAT3/FUNDC1 signaling could be a new therapeutic target for SIMD.

Keywords: FUNDC1; MAMs; calcium signaling; mitophagy; sepsis-induced myocardial dysfunction

DOI: https://doi.org/10.3389/fcvm.2021.790612