Background & Aims: Transporters of the SLC25 mitochondrial carrier superfamily bridge cytoplasmic and mitochondrial metabolism by channeling metabolites across mitochondrial membranes and are pivotal for metabolic homeostasis. Despite their physiological relevance as gatekeepers of cellular meta-bolism, most of the SLC25 family members remain uncharac-terized. We undertook a comprehensive tissue distribution analysis of all Slc25 family members across metabolic organs and identified SLC25A47 as a liver-specific mitochondrial carrier. Methods: We used a murine loss-of-function model to unravel the role of this transporter in mitochondrial and hepatic ho-meostasis. We performed extensive metabolic phenotyping and molecular characterization of newly generated Slc25a47hep-/-and Slc25a47-Fgf21(hep-)/-mice. Results: Slc25a47hep-/-mice displayed a wide variety of metabolic abnormalities, as a result of sustained energy deficiency in the liver originating from impaired mitochondrial respiration. This mitochondrial phenotype was associated with an activation of the mitochondrial stress response (MSR) in the liver, and the development of fibrosis, which was exacerbated upon feeding a high-fat high-sucrose diet. The MSR induced the secretion of several mitokines, amongst which FGF21 played a preponderant role on systemic physiology. To dissect the FGF21-dependent and-independent physiological changes induced in Slc25a47hep-/-mice, we generated a double Slc25a47-Fgf21(hep)-/-mouse model and demonstrated that several aspects of the hypermetabolic state were driven by hepatic secretion of FGF21. On the other hand, the metabolic fuel inflexibility observed in Slc25a47(hep)-/-mice could not be rescued with the genetic removal of Fgf21. Conclusion: Collectively, our data place the Slc25a47 locus at the center of mitochondrial homeostasis, which upon dysfunction triggers robust liver-specific and systemic adaptive stress responses. The prominent role of the Slc25a47 locus in hepatic fibrosis identifies this carrier, or its transported metabolite, as a potential target for therapeutic intervention.Lay summary: Herein, we report the importance of a locus containing a liver-specific gene coding for a mitochondrial transport protein called SLC25A47. Mitochondria are the powerhouses of cells. They are crucial for metabolism and energy generation. We show that mice with genetic disruption of the Slc25a47 locus cannot maintain mitochondrial homeostasis (balance), leading to wide-ranging problems in the liver that have far-reaching physiological consequences. (C) 2022 The Author(s). Published by Elsevier B.V.