Mitofusin 2 (MFN2), an outer mitochondrial membrane protein expressed in virtually all human tissues, is a multi-faceted protein known to affect mitochondrial morphology, metabolism, tethering, and movement as well as overall cell cycle progression. Most intriguing among its characteristics is its ability to bind to Ras and Raf, upstream effectors in the MAPK/ERK pathway. Conditional knockout (cKO) of renal proximal tubule MFN2 in vivo showed a post-ischemic protective effect. While the two day survival of control mice was only 28%, an unexpected 86% of the MFN2 cKO mice were alive at two days post-ischemia. This is likely explained by MFN2's ability to bind and sequester Ras at baseline. Because the MFN2 deficient mice did not sequester as much Ras, renal proximal tubule cells were able to proliferate at a greater rate and restore organ function more quickly. Immunoprecipitation studies confirm a strong interaction between Ras and MFN2 in resting cells but a weaker one immediately following ischemic insult, even in cells replete with MFN2. These results suggest that blocking the MFN2-Ras interaction may be a novel method to treat acute kidney injury. A small peptide mimicking Ras to block MFN2 could be feasible. This should grant ischemic tissue an increased propensity to regenerate healthy cells while leaving non-ischemic tissue completely unaffected. Such a therapeutic agent would be novel in the treatment of acute kidney injury and may have uses in other tissues as well due to MFN2's widespread expression profile.

<p>  </p> <p>Zebrafish (<em>Danio rerio</em>) is a well-established model to study neutrophil biology. However, a lack of standard tissue-specific knockdown or knockout technique in the zebrafish field has limited the power of this model organism when studying developmental essential genes, such as those related to mitochondrial function. We have developed a robust and flexible neutrophil-restricted knockout in zebrafish based on CRISPR/Cas9 system, with which we gained insights into the role of Rac2 in regulating the actin cytoskeleton and the subcellular location of Rac activation in zebrafish neutrophils.</p> <p>Previous study in our lab using another neutrophil-specific knockout system addressed multiple mitochondrial proteins regulate neutrophil motility in zebrafish. Interestingly, we observed <em>Mfn2</em>-deficient neutrophils trapped in the vasculature in zebrafish embryos. Here we further characterized the function of MFN2 in regulating cell migration with neutrophil-like HL-60 cells and mice embryonic fibroblasts (MEFs). We found significant changes in actin organization in both <em>MFN2</em>-deficient neutrophil-like cells and MEFs and mechanistically, disrupted mitochondria-ER interaction, increased intracellular Ca2+ levels. We also investigated the cytoskeleton proteins and observed hyperactivation of RhoA and Myosin light chain kinase, along with accumulation of phosphorylated myosin light chain at the cell boundary in <em>MFN2</em>-deficient MEFs. These altered MFN2-Ca2+-RhoA/MLCK-myosin signaling finally affects the peripheral actin bundle architecture and forms the “Peripheral Actin Myosin Belt (PAMB)” structure. The formation of PAMB hampered cell adhesive migration in <em>Mfn2</em>-null MEFs. </p> <p>Altogether, our research gained new insights into the essential role of MFN2 in cytoskeleton regulation and the underlying molecular mechanisms, which may provide a new direction to understand the relevance of this gene in immune cell dysfunction and other MFN2-associated diseases.</p>