Preclinical evaluation of candidate “kill or cure” strategies to treat MFN2-related lipodystrophy

Background: The mitofusin 2 (MFN2) R707W mutation causes debilitating human lipodystrophy featuring lower body adipose loss, upper body adipose hyperplasia, and dyslipidaemic insulin resistance. Mechanical complications include airway compromise due to head and neck adipose overgrowth. This condition, sometimes called Multiple Symmetrical Lipomatosis (MSL), is also seen in sporadic form strongly associated with excess ethanol consumption. Mitigating the cellular pathology, or, conversely, exacerbating it, inducing selective death of affected adipocytes, are potential therapeutic strategies. Methods: Candidate exacerbating and mitigating approaches to MFN2-MSL were tested in human MFN2R707W/R707W fibroblasts, and in Mfn2R707W/R707W mice and derived preadipocytes. Cell survival, mitochondrial network morphology and integrated stress response markers were assessed in cells, and body composition and metabolic indices in mice. Results: Forcing galactose metabolism in human MFN2R707W/R707W dermal fibroblasts did not replicate the overt adipose mitochondrial phenotype. 50mmol ethanol had little effect on Mfn2R707W/R707W white preadipocytes, but increased mitochondrial content and blunted mitolysosome formation in Mfn2R707W/R707W brown preadipocytes. 20% EtOH consumption increased brown adipose tissue in female Mfn2R707W/R707Wmice, and serum lactate in males. Rapamycin – a candidate mitigating treatment - increased size and mitolysosome content of WT preadipocytes, and to a lesser degree of Mfn2R707W/R707W preadipocytes. In male Mfn2R707W/R707W mice, rapamycin reduced weight gain, brown adipose mass, and increased serum Fgf21. Finally, a panel of mitochondrial stressors solicited no selective death or ISR in Mfn2R707W/R707W preadipocytes. Conclusions: Ethanol mildly exacerbates murine MFN2-related MSL, while rapamycin is tolerated. MFN2-related MSL may not be solely attributable to compromised oxidative phosphorylation.