Mitofusin 2 but not mitofusin 1 mediates Bcl-XL-induced mitochondrial aggregation

Controllable mitochondrial regulation based on photo-triggered DNA circuitry

DNA circuits have been widely used in the regulation of biomolecules and biochemical reactions due to their excellent controllability and responsiveness, but their regulation of intracellular organelles is still limited. Herein, we develop a photo-triggered mitochondrial regulation strategy based on a hybridization chain reaction (HCR) in living cells. In the design, the initial DNA hairpin is locked by a photocleavable group, and the assembling DNA hairpin pairs are tagged with triphenylphosphine for mitochondrial binding. Upon irradiation with UV light, the initiator hairpin is cleaved to trigger the HCR between triphenylphosphine-labeled hairpin pairs, followed by forming a long double-stranded DNA polymer for several of the mitochondria regulations in living cells. Our results demonstrate that mitochondrial regulation based on the HCR can successfully repair ROS stressed cells. Together, this work provides a new strategy for the spatiotemporally controlled regulation of intracellular mitochondria, exhibiting great potential in precision therapy.

Balancing life and death: BCL-2 family members at diverse ER-mitochondrial contact sites

The outer mitochondrial membrane is a busy place. One essential activity for cellular survival is the regulation of membrane integrity by the BCL-2 family of proteins. Another critical facet of the outer mitochondrial membrane is its close approximation with the endoplasmic reticulum. These mitochondrial-associated membranes (MAMs) occupy a significant fraction of the mitochondrial surface and serve as key signaling hubs for multiple cellular processes. Each of these pathways may be considered as forming their own specialized MAM subtype. Interestingly, like membrane permeabilization, most of these pathways play critical roles in regulating cellular survival and death. Recently, the pro-apoptotic BCL-2 family member BOK has been found within MAMs where it plays important roles in their structure and function. This has led to a greater appreciation that multiple BCL-2 family proteins, which are known to participate in numerous functions throughout the cell, also have roles within MAMs. In this review, we evaluate several MAM subsets, their role in cellular homeostasis, and the contribution of BCL-2 family members to their functions.

High spatio-temporal resolution measurement of A1 R and A2A R interactions combined with Iem-spFRET and E-FRET methods

A₁ R-A_2A R heterodimers regulate striatal glutamatergic neurotransmission. However, few researches about kinetics have been reported. Here, we combined Iem-spFRET and E-FRET to investigate the kinetics of A₁ R and A_2A R interaction. Iem-spFRET obtains the energy transfer efficiency of the whole cell. E-FRET gets energy transfer efficiency with high spatial resolution, whereas, it was prone to biases because background was easily selected due to manual operation. To study the interaction with high spatio-temporal resolution, Iem-spFRET was used to correct the deviation of E-FRET. In this paper, A₁ R and A_2A R interaction was monitored, and the changes of FRET efficiency of the whole or/and partial cell membrane were described. The results showed that activation of A₁ R or A_2A R leads to rapid aggregation, inhibition of A₁ R or A_2A R leads to slow segregation, and the interaction is reversible. These results demonstrated that combination of Iem-spFRET and E-FRET could measure A₁ R and A_2A R interaction with high spatio-temporal resolution.

Optical section structured illumination-based Förster resonance energy transfer imaging

Förster resonance energy transfer (FRET) microscopy is an important tool suitable for studying molecular interactions in living cells. Optical section structured illumination microscopy (OS-SIM), like confocal microscopy, has about 200 nm spatial resolution. In this report, we performed quantitative 3-cube FRET imaging in OS-SIM mode and widefield microscopy (WF) mode, respectively, for living cells expressing FRET constructs consisting of Cerulean (C, donor) and Venus (V, acceptor). OS-SIM images exhibited higher resolution than WF images. Four spectral crosstalk coefficients measured under OS-SIM mode are consistent with those measured under WF mode. Similarly, the system calibration factors G and k measured under OS-SIM mode were consistent with those measured under WF mode. The measured FRET efficiency (E) values of C32V and C17V as well as C5V constructs, standard FRET plasmids, in living Hela cells were E C 32 V OSF = 0.32 ± 0.02 , E C 17 V OSF = 0.38 ± 0.02 , and E C 5 V OSF = 0.45 ± 0.03 , and the measured acceptor-to-donor concentration ratios ( R c ) were R C 32 V OSF = 1.07 ± 0.03 , R C 17 V OSF = 1.09 ± 0.03 , and R C 5 V OSF = 1.02 ± 0.04 , consistent with the reported values. Collectively, our data demonstrates that OS-SIM can be integrated into FRET microscopy to build an OS-SIM-FRET with confocal microscopy-like resolution.

Mitochondrial Fusion Protein Mfn2 and Its Role in Heart Failure

Mitofusin 2 (Mfn2) is a transmembrane GTPase located on the mitochondrial outer membrane that contributes to mitochondrial network regulation. It is an essential multifunctional protein that participates in various biological processes under physical and pathological conditions, including mitochondrial fusion, reticulum-mitochondria contacts, mitochondrial quality control, and apoptosis. Mfn2 dysfunctions have been found to contribute to cardiovascular diseases, such as ischemia-reperfusion injury, heart failure, and dilated cardiomyopathy. Here, this review mainly focuses on what is known about the structure and function of Mfn2 and its crucial role in heart failure.