Drp1 Mitochondrial Fission in D1 Neurons Mediates Behavioral and Cellular Plasticity during Early Cocaine Abstinence.

Altered brain energy homeostasis is a key adaptation occurring in the cocaine-addicted brain, but the effect of cocaine on the fundamental source of energy, mitochondria, is unknown. We demonstrate an increase of dynamin-related protein-1 (Drp1), the mitochondrial fission mediator, in nucleus accumbens (NAc) after repeated cocaine exposure and in cocaine-dependent individuals. Mdivi-1, a demonstrated fission inhibitor, blunts cocaine seeking and locomotor sensitization, while blocking c-Fos induction and excitatory input onto dopamine receptor-1 (D1) containing NAc medium spiny neurons (MSNs). Drp1 and fission promoting Drp1 are increased in D1-MSNs, consistent with increased smaller mitochondria in D1-MSN dendrites after repeated cocaine. Knockdown of Drp1 in D1-MSNs blocks drug seeking after cocaine self-administration, while enhancing the fission promoting Drp1 enhances seeking after long-term abstinence from cocaine. We demonstrate a role for altered mitochondrial fission in the NAc, during early cocaine abstinence, suggesting potential therapeutic treatment of disrupting mitochondrial fission in cocaine addiction.

Novel regulatory roles of Mff and Drp1 in E3 ubiquitin ligase MARCH5-dependent degradation of MiD49 and Mcl1 and control of mitochondrial dynamics.

MARCH5, an OMM-associated E3 ubiquitin ligase, controls mitochondrial function. Despite its importance, the mechanism and factors controlling MARCH5 activity are largely unknown. Here we report that the MARCH5 C-terminal domain plays a critical role in degradation of MARCH5 substrates, likely by facilitating release of ubiquitinated proteins from the OMM. We also found that the mitochondrial fission proteins Drp1 and Mff negatively regulate MARCH5's activity toward MiD49 and Mcl1. Knockouts of either Drp1 or Mff led to reduced expression, shorter half-lives, and increased ubiquitination of MiD49 and Mcl1. Effects of Mff and Drp1 depletion on degradation rates and ubiquitination of Mcl1 and MiD49 were eliminated in Drp1-/-/MARCH5-/- and Mff-/-/MARCH5-/- cells. Our data show that it is not mitochondrial morphology per se but rather Mff and Drp1 that directly control MARCH5. Consistently, we find that Mff is an integral component of the MARCH5/p97/Npl4 complex, which is also controlled by MARCH5's C-terminal domain. Furthermore, not only mitochondrial fission but also fusion is regulated through Mff and Drp1 protein activities. Thus, in addition to their canonical roles in mitochondrial fission, Mff and Drp1 also act as regulatory factors that control mitochondrial fission and fusion.

Mitochondrial E3 ubiquitin ligase MARCH5 controls mitochondrial fission and cell sensitivity to stress-induced apoptosis through regulation of MiD49 protein.

Ubiquitin- and proteasome-dependent outer mitochondrial membrane (OMM)-associated degradation (OMMAD) is critical for mitochondrial and cellular homeostasis. However, the scope and molecular mechanisms of the OMMAD pathways are still not well understood. We report that the OMM-associated E3 ubiquitin ligase MARCH5 controls dynamin-related protein 1 (Drp1)-dependent mitochondrial fission and cell sensitivity to stress-induced apoptosis. MARCH5 knockout selectively inhibited ubiquitination and proteasomal degradation of MiD49, a mitochondrial receptor of Drp1, and consequently led to mitochondrial fragmentation. Mitochondrial fragmentation in MARCH5(-/-) cells was not associated with inhibition of mitochondrial fusion or bioenergetic defects, supporting the possibility that MARCH5 is a negative regulator of mitochondrial fission. Both MARCH5 re-expression and MiD49 knockout in MARCH5(-/-) cells reversed mitochondrial fragmentation and reduced sensitivity to stress-induced apoptosis. These findings and data showing MARCH5-dependent degradation of MiD49 upon stress support the possibility that MARCH5 regulation of MiD49 is a novel mechanism controlling mitochondrial fission and, consequently, the cellular response to stress.

Two smalls in one: Coincident small cell carcinoma and small lymphocytic lymphoma in a lymph node diagnosed by fine-needle aspiration biopsy.

BACKGROUND: B-cell chronic lymphocytic leukemia / small lymphocytic lymphoma (CLL / SLL) is one of the most common lymphoproliferative disorders in western countries. Patients with SLL / CLL are at increased risk of site-specific secondary cancers. We present a unique case of a 71-year-old male, with a history of SLL / CLL, who presented with pulmonary symptoms and a mediastinal mass. Fine needle aspiration (FNA) of the mediastinal lymph node revealed synchronous SLL / CLL and small cell carcinoma (SCC). MATERIALS AND METHODS: The patient underwent a computed tomography (CT) scan of the chest and endobronchial ultrasound-guided transbronchial fine needle aspiration of the mediastinal lymph node (4R). The sample was submitted for cytopathology, immunohistochemical stains, and flow cytometry evaluation. RESULTS: Fine needle aspiration of the mediastinal lymph node revealed neoplastic cells, in clusters and singly, with cytological features suggestive of small cell carcinoma. The immunohistochemistry results confirmed this diagnosis. Small-to-medium, mature-appearing lymphocytes were also present in the background. Flow cytometry analysis revealed that these lymphocytes possessed an immunophenotype consistent with CLL / SLL. CONCLUSIONS: This case illustrates the importance of a pathologist's awareness of the possibility of concurrent lymphoma and metastatic carcinoma in a lymph node. When evaluating lymph nodes, pathologists must strive to identify both foreign cells and subtle lymphoid changes. As demonstrated by our case, ancillary techniques (such as immunohistochemistry and flow cytometry) can be critical to making a complete and accurate diagnosis. The diagnosis of small cell carcinoma in the enlarged lymph node, primarily harboring CLL / SLL, is of critical importance for decision-making and treatment purposes, in addition to having a significant adverse impact on the overall survival.