Age-related MICOS Complex Dysregulation Impairs Mitochondrial 3D Architecture and Metabolic Homeostasis in the Liver

Background & AimsAging is associated with a significant decline in mitochondrial function in the liver, leading to an increased risk of liver disease. This study examines age-related changes in the mitochondrial structure of human and murine livers using a combination of Serial Block-Face Scanning Electron Microscopy (SBF-SEM) and mass spectrometry approaches. MethodsThis study integrates mitochondrial structure analysis in a murine model with an analysis of liver architecture, lipogenesis, and genetically regulated gene expression in human cohorts. We explored the Mitochondrial Contact Site and Cristae Organizing System (MICOS) complex using SBF-SEM, three-dimensional reconstruction with Amira software, and mass spectrometry techniques. ResultsAging leads to a reduction in mitochondrial size and complexity, resulting in changes in the metabolomic and lipidomic profiles of murine liver cells that are comparable to those observed in aged human samples. We find that genetically modeled expression of MICOS complex genes OPA1 and CHCHD3 is associated with chronic liver disease phenotypes within a large biobank population. Furthermore, we observed dysregulated mitochondrial calcium handling and increased oxidative stress due to the disruption of the MICOS complex. ConclusionOur study highlights the age-associated decline in mitochondrial complexity and metabolic regulation within the aging murine liver and the human population. We have identified that these changes are partially attributable to the age-related loss of the MICOS complex. Impact and implicationsThis study offers new insights into the changes to mitochondrial ultrastructure that occur during aging. Using SBF-SEM, the quantification of young and aged murine mitochondrial structure was performed, which had previously been an underexplored avenue for measuring mitochondrial changes. The discovery of mitochondrial ultrastructural changes, in conjunction with measurements of age-associated metabolic alterations and gene association data, provides a model for how changes in MICOS expression may modulate age-related impairment of hepatic mitochondria. These results provide a new model by which changes in MICOS protein expression may both cause and be a potential therapeutic target for age-related impairment in hepatic function. HighlightsDecreased modeled expression of CHCHD3 in individuals of European genetic ancestry is linked to liver transplant and cirrhosis, while decreased modeled expression of OPA1 in individuals of African genetic ancestry is associated with chronic liver disease and cirrhosis. Aging alters liver lipid accumulation, MICOS mRNA levels, and disease markers. Aging reduces the volume and complexity of murine liver ultrastructure. Aging and diet significantly alter the MICOS complex in mice. Knockdown of Mic60 and Chchd6 lowers Ca2+ uptake, retention, and induces oxidative stress in HepG2 cells. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=139 SRC="FIGDIR/small/599846v3_ufig1.gif" ALT="Figure 1000"> View larger version (47K): org.highwire.dtl.DTLVardef@1cdd61corg.highwire.dtl.DTLVardef@a3fb74org.highwire.dtl.DTLVardef@1d1ad36org.highwire.dtl.DTLVardef@c2e55f_HPS_FORMAT_FIGEXP M_FIG C_FIG Liver aging causes metabolic, lipidomic, and mitochondrial structural alterations, reflecting age-dependent losses in the MICOS complex. Key components of the MICOS complex (MIC60, CHCHD3 and CHCHD6) are illustrated.