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Dynamic interaction of REEP5-MFN1/2 enables mitochondrial hitchhiking on tubular ER

Mitochondrial functions can be regulated by membrane contact sites with the endoplasmic reticulum (ER). These mitochondria-ER contact sites (MERCs) are functionally heterogeneous and maintained by various tethers. Here, we found that REEP5, an ER tubule-shaping protein, interacts with Mitofusins 1/2 to mediate mitochondrial distribution throughout the cytosol by a new transport mechanism, mitochondrial "hitchhiking" with tubular ER on microtubules. REEP5 depletion led to reduced tethering and increased perinuclear localization of mitochondria. Conversely, increasing REEP5 expression facilitated mitochondrial distribution throughout the cytoplasm. Rapamycin-induced irreversible REEP5-MFN1/2 interaction led to mitochondrial hyperfusion, implying that the dynamic release of mitochondria from tethering is necessary for normal mitochondrial distribution and dynamics. Functionally, disruption of MFN2-REEP5 interaction dynamics by forced dimerization or silencing REEP5 modulated the production of mitochondrial reactive oxygen species (ROS). Overall, our results indicate that dynamic REEP5-MFN1/2 interaction mediates cytosolic distribution and connectivity of the mitochondrial network by "hitchhiking" and this process regulates mitochondrial ROS, which is vital for multiple physiological functions.

The N-terminal signature motif on the transporter MCT1 is critical for CD147-mediated trafficking

The human Solute Carrier (SLC) family member, monocarboxylate transporter 1 (MCT1), transports lactic and pyruvic acid across biological membranes to regulate cellular pH and metabolism. Proper trafficking of MCT1 from the endoplasmic reticulum to the plasma membrane hinges on its interactions with the membrane-bound chaperone protein, CD147. Here, using AlphaFold2 modeling and copurification, we show how a conserved signature motif located in the flexible N-terminus of MCT1 is a crucial region of interaction between MCT1 and the C-terminus of CD147. Mutations to this motif-namely, the thymic cancer linked G19C and the highly conserved W20A-destabilize the MCT1-CD147 complex and lead to a loss of proper membrane localization and cellular substrate flux. Notably, the monomeric stability of MCT1 remains unaffected in mutants, thus supporting the role of CD147 in mediating the trafficking of the heterocomplex. Using the auxiliary chaperone, GP70, we demonstrated that W20A-MCT1 can be trafficked to the plasma membrane, while G19C-MCT1 remains internalized. Overall, our findings underscore the critical role of the MCT1 transmembrane one signature motif for engaging CD147 and identify altered chaperone binding mechanisms between the CD147 and GP70 glycoprotein chaperones.

In vivo inhibition of nuclear ACE2 translocation protects against SARS-CoV-2 replication and lung damage through epigenetic imprinting

In vitro, ACE2 translocates to the nucleus to induce SARS-CoV-2 replication. Here, using digital spatial profiling of lung tissues from SARS-CoV-2-infected golden Syrian hamsters, we show that a specific and selective peptide inhibitor of nuclear ACE2 (NACE2i) inhibits viral replication two days after SARS-CoV-2 infection. Moreover, the peptide also prevents inflammation and macrophage infiltration, and increases NK cell infiltration in bronchioles. NACE2i treatment increases the levels of the active histone mark, H3K27ac, restores host translation in infected hamster bronchiolar cells, and leads to an enrichment in methylated ACE2 in hamster bronchioles and lung macrophages, a signature associated with virus protection. In addition, ACE2 methylation is increased in myeloid cells from vaccinated patients and associated with reduced SARS-CoV-2 spike protein expression in monocytes from individuals who have recovered from infection. This protective epigenetic scarring of ACE2 is associated with a reduced latent viral reservoir in monocytes/macrophages and enhanced immune protection against SARS-CoV-2. Nuclear ACE2 may represent a therapeutic target independent of the variant and strain of viruses that use the ACE2 receptor for host cell entry.

Independent control over cell patterning and adhesion on hydrogel substrates for tissue interface mechanobiology

Tissue boundaries and interfaces are engines of morphogenesis in vivo. However, despite a wealth of micropatterning approaches available to control tissue size, shape, and mechanical environment in vitro, fine-scale spatial control of cell positioning within tissue constructs remains an engineering challenge. To address this, we augment DNA "velcro" technology for selective patterning of ssDNA-labeled cells on mechanically defined photoactive polyacrylamide hydrogels. Hydrogels bearing photopatterned single-stranded DNA (ssDNA) features for cell capture are then co-functionalized with extracellular matrix (ECM) proteins to support subsequent adhesion of patterned tissues. ECM protein co-functionalization does not alter ssDNA pattern fidelity, cell capture, or hydrogel elastic stiffness. This approach enables mechanobiology studies and measurements of signaling activity at dynamic cell interfaces with precise initial patterning. Combining DNA velcro patterning and ECM functionalization provides independent control of initial cell placement, adhesion, and mechanics, constituting a new tool for studying biological interfaces and for programming multicellular interactions in engineered tissues.

Optogenetic Tools for Control of Public Goods in Saccharomyces cerevisiae

Microorganisms live in dense and diverse communities, with interactions between cells guiding community development and phenotype. The ability to perturb specific intercellular interactions in space and time provides a powerful route to determining the critical interactions and design rules for microbial communities. Approaches using optogenetic tools to modulate these interactions offer promise, as light can be exquisitely controlled in space and time. We report new plasmids for rapid integration of an optogenetic system into Saccharomyces cerevisiae to engineer light control of expression of a gene of interest. In a proof-of-principle study, we demonstrate the ability to control a model cooperative interaction, namely, the expression of the enzyme invertase (SUC2) which allows S. cerevisiae to hydrolyze sucrose and utilize it as a carbon source. We demonstrate that the strength of this cooperative interaction can be tuned in space and time by modulating light intensity and through spatial control of illumination. Spatial control of light allows cooperators and cheaters to be spatially segregated, and we show that the interplay between cooperative and inhibitory interactions in space can lead to pattern formation. Our strategy can be applied to achieve spatiotemporal control of expression of a gene of interest in S. cerevisiae to perturb both intercellular and interspecies interactions.

IMPORTANCE Recent advances in microbial ecology have highlighted the importance of intercellular interactions in controlling the development, composition, and resilience of microbial communities. In order to better understand the role of these interactions in governing community development, it is critical to be able to alter them in a controlled manner. Optogenetically controlled interactions offer advantages over static perturbations or chemically controlled interactions, as light can be manipulated in space and time and does not require the addition of nutrients or antibiotics. Here, we report a system for rapidly achieving light control of a gene of interest in the important model organism Saccharomyces cerevisiae and demonstrate that by controlling expression of the enzyme invertase, we can control cooperative interactions. This approach will be useful for understanding intercellular and interspecies interactions in natural and synthetic microbial consortia containing S. cerevisiae and serves as a proof of principle for implementing this approach in other consortia.

Ecm29-Dependent Proteasome Localization Regulates Cytoskeleton Remodeling at the Immune Synapse

The formation of an immune synapse (IS) enables B cells to capture membrane-tethered antigens, where cortical actin cytoskeleton remodeling regulates cell spreading and depletion of F-actin at the centrosome promotes the recruitment of lysosomes to facilitate antigen extraction. How B cells regulate both pools of actin, remains poorly understood. We report here that decreased F-actin at the centrosome and IS relies on the distribution of the proteasome, regulated by Ecm29. Silencing Ecm29 decreases the proteasome pool associated to the centrosome of B cells and shifts its accumulation to the cell cortex and IS. Accordingly, Ecm29-silenced B cells display increased F-actin at the centrosome, impaired centrosome and lysosome repositioning to the IS and defective antigen extraction and presentation. Ecm29-silenced B cells, which accumulate higher levels of proteasome at the cell cortex, display decreased actin retrograde flow in lamellipodia and enhanced spreading responses. Our findings support a model where B the asymmetric distribution of the proteasome, mediated by Ecm29, coordinates actin dynamics at the centrosome and the IS, promoting lysosome recruitment and cell spreading.

Autophagy impairment as a key feature for acetaminophen-induced ototoxicity

Macroautophagy/autophagy is a highly conserved self-digestion pathway that plays an important role in cytoprotection under stress conditions. Autophagy is involved in hepatotoxicity induced by acetaminophen (APAP) in experimental animals and in humans. APAP also causes ototoxicity. However, the role of autophagy in APAP-induced auditory hair cell damage is unclear. In the present study, we investigated autophagy mechanisms during APAP-induced cell death in a mouse auditory cell line (HEI-OC1) and mouse cochlear explant culture. We found that the expression of LC3-II protein and autophagic structures was increased in APAP-treated HEI-OC1 cells; however, the degradation of SQSTM1/p62 protein, the yellow puncta of mRFP-GFP-LC3 fluorescence, and the activity of lysosomal enzymes decreased in APAP-treated HEI-OC1 cells. The degradation of p62 protein and the expression of lysosomal enzymes also decreased in APAP-treated mouse cochlear explants. These data indicate that APAP treatment compromises autophagic degradation and causes lysosomal dysfunction. We suggest that lysosomal dysfunction may be directly responsible for APAP-induced autophagy impairment. Treatment with antioxidant N-acetylcysteine (NAC) partially alleviated APAP-induced autophagy impairment and apoptotic cell death, suggesting the involvement of oxidative stress in APAP-induced autophagy impairment. Inhibition of autophagy by knocking down of Atg5 and Atg7 aggravated APAP-induced ER and oxidative stress and increased apoptotic cell death. This study provides a better understanding of the mechanism responsible for APAP ototoxicity, which is important for future exploration of treatment strategies for the prevention of hearing loss caused by ototoxic medications.