AKAP350C targets to mitochondria via a novel amphipathic alpha helical domain

Mid51/Fis1 mitochondrial oligomerization complex drives lysosomal untethering and network dynamics

Lysosomes are highly dynamic organelles implicated in multiple diseases. Using live super-resolution microscopy, we found that lysosomal tethering events rarely undergo lysosomal fusion, but rather untether over time to reorganize the lysosomal network. Inter-lysosomal untethering events are driven by a mitochondrial Mid51/Fis1 complex that undergoes coupled oligomerization on the outer mitochondrial membrane. Importantly, Fis1 oligomerization mediates TBC1D15 (Rab7-GAP) mitochondrial recruitment to drive inter-lysosomal untethering via Rab7 GTP hydrolysis. Moreover, inhibiting Fis1 oligomerization by either mutant Fis1 or a Mid51 oligomerization mutant potentially associated with Parkinson’s disease prevents lysosomal untethering events, resulting in misregulated lysosomal network dynamics. In contrast, dominant optic atrophy–linked mutant Mid51, which does not inhibit Mid51/Fis1 coupled oligomerization, does not disrupt downstream lysosomal dynamics. As Fis1 conversely also regulates Mid51 oligomerization, our work further highlights an oligomeric Mid51/Fis1 mitochondrial complex that mechanistically couples together both Drp1 and Rab7 GTP hydrolysis machinery at mitochondria–lysosome contact sites. These findings have significant implications for organelle networks in cellular homeostasis and human disease.

Lysosomal Regulation of Inter-mitochondrial Contact Fate and Motility in Charcot-Marie-Tooth Type 2

Properly regulated mitochondrial networks are essential for cellular function and implicated in multiple diseases. Mitochondria undergo fission and fusion events, but the dynamics and regulation of a third event of inter-mitochondrial contact formation remain unclear. Using super-resolution imaging, we demonstrate that inter-mitochondrial contacts frequently form and play a fundamental role in mitochondrial networks by restricting mitochondrial motility. Inter-mitochondrial contact untethering events are marked and regulated by mitochondria-lysosome contacts, which are modulated by RAB7 GTP hydrolysis. Moreover, inter-mitochondrial contact formation and untethering are further regulated by Mfn1/2 and Drp1 GTP hydrolysis, respectively. Surprisingly, endoplasmic reticulum tubules are also present at inter-mitochondrial contact untethering events, in addition to mitochondrial fission and fusion events. Importantly, we find that multiple Charcot-Marie-Tooth type 2 disease-linked mutations in Mfn2 (CMT2A), RAB7 (CMT2B), and TRPV4 (CMT2C) converge on prolonged inter-mitochondrial contacts and defective mitochondrial motility, highlighting a role for inter-mitochondrial contacts in mitochondrial network regulation and disease.

Mitochondrial cAMP signaling

Cyclic adenosine 3, 5'-monophosphate (cAMP) is a ubiquitous second messenger regulating many biological processes, such as cell migration, differentiation, proliferation and apoptosis. cAMP signaling functions not only on the plasma membrane, but also in the nucleus and in organelles such as mitochondria. Mitochondrial cAMP signaling is an indispensable part of the cytoplasm-mitochondrion crosstalk that maintains mitochondrial homeostasis, regulates mitochondrial dynamics, and modulates cellular stress responses and other signaling pathways. Recently, the compartmentalization of mitochondrial cAMP signaling has attracted great attentions. This new input should be carefully taken into account when we interpret the findings of mitochondrial cAMP signaling. In this review, we summarize previous and recent progress in our understanding of mitochondrial cAMP signaling, including the components of the signaling cascade, and the function and regulation of this signaling pathway in different mitochondrial compartments.