Mechanisms of mitochondria-driven hepatocyte injury - PROJECT SUMMARY The prevalence of metabolic disease is growing rapidly, driven predominantly by increasing incidence of obesity and metabolic-associated steatohepatitis (MASH). However, there are very limited therapies for treating liver injury, placing these as a growing area of unmet clinical need. One therapeutic approach for metabolic diseases has been to seek human gene variants conferring susceptibility or protection. Unfortunately, several of the top genetic targets have phenotypes in model systems that do not replicate human pathology, have loss-of-function phenotypes associated with higher injury risk, or are associated with worsening cardiovascular risk, complicating the development of drugs. Here, we propose to study a gene, EF-hand domain family member D1 (EFHD1), whose decreased hepatic expression in genome-wide analyses has been associated with protection from liver injury in multiple, racially-diverse human populations. The EFHD1 protein is targeted to the mitochondrial outer membrane, including areas interacting with the endoplasmic reticulum, and possesses Ca2+-binding EF hands. We find that mice without EFHD1 (Efhd1-/-) have no obvious adverse phenotypes at baseline, but are protected against liver injury during a metabolic challenge, replicating the human phenotype. Therefore, inhibiting EFHD1 may be a promising therapy for liver injury. Moreover, a widespread phenomenon noted in many organs, including the liver, is that overnutrition causes excessive mitochondrial fission through the release of Ca2+ from the ER. However, the critical transducer coupling ER Ca2+ release to mitochondrial fission has not been identified, despite decades of study. Here, we hypothesize that EFHD1 is, in fact, that critical transducer, providing a mechanistic understanding for why inhibiting it may be potentially beneficial in MASH. Our proposal comprises three aims. First, we will define whether EFHD1 is the critical adaptor facilitating Ca2+-dependent mitochondrial remodeling. Second, we will determine if loss of EFHD1 leads to altered fatty acid oxidation. Finally, we will test whether loss of EFHD1 is protective against hepatocyte damage and subsequent inflammatory responses in mouse models of MASH and liver injury. Our collaborative team of investigators combines expertise in mitochondrial Ca2+ signaling, mouse and human studies of liver disease, and rigorous metabolic phenotyping, and is well-poised to tackle this project. In summary, the series of experiments detailed in this proposal will reveal the mechanism of EFHD1 action, and establish whether targeting this pathway may be protective against liver injury, as seen in human genetic analyses.
