The Mitofusin 2 protein (MFN2), encoded by the MFN2 gene, was first described for its role in mediating mitochondrial fusion. However, MFN2 is now recognized to play additional roles in mitochondrial autophagy (mitophagy), mitochondrial motility, lipid transfer, and as a tether to other organelles including the endoplasmic reticulum (ER) and lipid droplets. The tethering role of MFN2 is an important mediator of mitochondrial-ER contact sites (MERCs), which themselves have many important functions that regulate mitochondria, including calcium homeostasis and lipid metabolism. Exemplifying the importance of MFN2, pathogenic variants in MFN2 are established to cause the peripheral neuropathy Charcot-Marie-Tooth Disease Subtype 2A (CMT2A). However, the mechanistic basis for disease is not clear. Moreover, additional pathogenic phenotypes such as lipomatosis, distal myopathy, optic atrophy, and hearing loss, can also sometimes be present in patients with CMT2A. Given these variable patient phenotypes, and the many cellular roles played by MFN2, the mechanistic underpinnings of the cellular impairments by which MFN2 dysfunction leads to disease are likely to be complex. Here, we will review what is known about the various functions of MFN2 that are impaired by pathogenic variants causing CMT2A, with a specific emphasis on the ties between MFN2 variants and MERCs.

The crystal structure of gliclazide, N-[(perhydrocyclopenta [c]pyrrol-2-yl)aminocarbonyl]-p-toluenesulfonamide, C15H21B3O3S, a second-generation oral hypoglycemic agent, contains discrete molecules with normal molecular dimensions. Both of the five-membered fused rings adopt envelope conformations. The molecules are linked into chains by intermolecular hydrogen bonds involving amino-H atoms, with N...O separations of 2.967 (3) and 2.949 (3) A.

Background: Pathogenic variants in MFN2 cause Charcot-Marie-Tooth disease (CMT) type 2A (CMT2A) and are the leading cause of the axonal subtypes of CMT. CMT2A is characterized by predominantly distal motor weakness and muscle atrophy, with highly variable severity and onset age. Notably, some MFN2 variants can also lead to other phenotypes such as optic atrophy, hearing loss and lipodystrophy. Despite the clear link between MFN2 and CMT2A, our mechanistic understanding of how dysfunction of the MFN2 protein causes human disease pathologies remains incomplete. This lack of understanding is due in part to the multiple cellular roles of MFN2. Though initially characterized for its role in mediating mitochondrial fusion, MFN2 also plays important roles in mediating interactions between mitochondria and other organelles, such as the endoplasmic reticulum and lipid droplets. Additionally, MFN2 is also important for mitochondrial transport, mitochondrial autophagy, and has even been implicated in lipid transfer. Though over 100 pathogenic MFN2 variants have been described to date, only a few have been characterized functionally, and even then, often only for one or two functions. Method: Several MFN2-mediated functions were characterized in fibroblast cells from a patient presenting with cerebellar ataxia, deafness, blindness, and diffuse cerebral and cerebellar atrophy, who harbours a novel homozygous MFN2 variant, D414V, which is found in a region of the HR1 domain of MFN2 where few pathogenic variants occur. Results: We found evidence for impairment of several MFN2-mediated functions. Consistent with reduced mitochondrial fusion, patient fibroblasts exhibited more fragmented mitochondrial networks and had reduced mtDNA copy number. Additionally, patient fibroblasts had reduced oxygen consumption, fewer mitochondrial-ER contacts, and altered lipid droplets that displayed an unusual perinuclear distribution. Conclusion: Overall, this work characterizes D414V as a novel variant in MFN2 and expands the phenotypic presentation of MFN2 variants to include cerebellar ataxia.

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The ketogenic diet (KD) is clinically beneficial and has therapeutic potential access a growing list of neurological disorders, including autism spectrum disorder (ASD). However, the underlying mechanisms mediating the benefits of the KD, which can also have undesirable side effects, remain undefined. To this end, improvements in mitochondrial morphology and function correlate with improved ASD behaviours in response to the KD, though how the KD influences mitochondrial morphology, and whether this is sufficient to improve behaviour remains unknown. Here, we investigate how beta-hydroxybutyrate (βHB), a key metabolite produced by the KD regulates mitochondrial morphology, and whether this pathway could be exploited to improve ASD behaviours. We found that β-oxidation of ΒHB promotes mitochondrial elongation by increasing NAD+ levels, which in turn activates SIRT deacetylases that act on key regulators of both mitochondrial fusion and fission. Our data suggest that increasing NAD+ levels with its precursor, nicotinamide nucleotide (NMN), is sufficient to promote mitochondrial hyperfusion. Finally, both ΒHB and NMN improve locomotor behaviour in the shank3+/- zebrafish model of ASD. Together, our findings elucidate a mechanism by which the ketogenic diet promotes mitochondrial elongation. Moreover, manipulation of this pathway may provide a novel avenue for the treatment of neurological disorders such as ASD, one which may obviate potential complications of the KD in clinical practice.