Changes in spinal cord mitochondria with high fat diet consumption: Implications for the trajectory of recovery after spinal cord injury
Langley M, Yoon H, Kim H, Lanza I, Matveyenko A, LeBrasseur N, Scarisbrick I
Mayo Clinic, Rochester, MN, United states
Objective: Obesity and metabolic syndrome cause detrimental effects on mitochondria in various tissues including liver and muscle, but the specific effects on the intact spinal cord or in the context of injury is largely unexplored. Importantly, it was recently shown that changes in mitochondrial morphology and function occur following acute spinal cord injury (SCI) (Jia et al, 2016). Here, we seek to illuminate metabolic and mitochondrial changes occurring in the spinal cord of adult mice with diet induced obesity and signs of metabolic syndrome.
Design/Methods: Adult male C57BL6 mice were fed a regular diet or a diet high in saturated fat for 4 or 12 wks. At 4 and 12 wks, SCs were collected for mitochondria isolation and high resolution respirometry. SCs were also collected at 12 weeks for RNA sequencing, protein quantification, and metabolomics approaches using LC-LC-MS. Immunohistochemical methods were also used to determine coordinate changes in mitochondrial health and oxidative stress related markers. Cell culture studies were used to address the impact of saturated fatty acids on neurons and glia, to dissect mechanisms involved, and to provide a platform to screen pharmacologic candidates capable of improving mitochondrial function.
Results: The spinal cords of mice consuming high fat for 4 wks had significantly higher state 3 and state 4 respiration as determined by high resolution respirometry in isolated spinal cord mitochondria. However, by 12 wks, state 4 mitochondrial respiration was significantly less and state 3 respiration was not changed compared to regular chow-fed mice. Moreover, citric acid cycle intermediates, isocitrate, alpha-ketoglutarate, and oxaloacetate were each depleted in the SC of mice consuming high fat for 12 wks compared to controls as shown by targeted metabolomics. RNA sequencing of the SCs of regular and high fat fed mice revealed changes in genes related to mitochondrial morphology, quality control processes, and oxidative stress response genes. Western blotting and qPCR analyses confirm that high fat induced mitochondrial changes in the adult SC. We also identified increased 4-HNE, a marker of oxidative stress, in the SCs of mice consuming high fat.
Finally, we characterized mitochondria functional and structural changes in response to palmitic acid, a saturated fatty acid, in murine neuron and glia cell cultures. Supporting in vivo findings that myelinating oligodendrocytes are reduced in the SC of mice consuming high fat (Yoon et al., 2016), we saw increased mitochondrial fragmentation and a reduced oxygen consumption rate (OCR) in oligodendrocytes cultured with palmitic acid. Astrocytes however, significantly increased OCR following exposure to the same fatty acids.
Conclusion: Our data suggest that changes in the adult SC in response to high fat consumption creates an environment that fosters secondary injury and is less conducive to neural repair by impacting mitochondria function and morphology. Understanding the cellular environment in response to dietary factors such as high fat consumption can help to guide care for individuals with SCI and identify new targets for intervention to create a more suitable cellular and molecular environment for tissue regeneration.
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