PDK4 and chronic kidney disease: Interestingly, elevated mRNA expression of pyruvate dehydrogenase kinase 4 (Pdk4), a negative regulator of pyruvate metabolism, was upregulated in male AHRfl/fl mice with CKD + probenecid but not AHRmKO mice (Supplemental Figure 3A), and this could explain the protection of OXPHOS observed in AHRmKO mice when pyruvate is the primary carbon source.