Mevalonate metabolites contribute to granulocyte chemotaxis and mortality in murine endotoxemia

Abstract

Statins appear to dramatically increase sepsis survival but only when treatment is initiated prior to hospitalization. This implies that statins exhibit a delayed-onset pro-survival benefit in septic patients that results in clinical futility of statin-therapy for patients already diagnosed with sepsis. Identification of mechanisms that contribute to increased sepsis-survival following statin-pretreatment may reveal novel therapeutic targets that do not suffer similar delayed onset benefits. Statins are used to treat hypercholesterolemia and function by inhibiting the production of the rate-limiting metabolite mevalonate. This indirectly inhibits the de novo synthesis of not only cholesterol but also isoprenoids that are involved in prenylation, the post-translational lipid modification of proteins. Mirroring clinical observations, chronic but not acute treatment with simvastatin significantly increased survival in a murine endotoxemia model. This was associated with reduced systemic granulocyte chemotaxis that occurred in a cell-intrinsic manner. In vitro modeling showed that simvastatin abolished chemoattractant responses and that this could be reversed by restoring geranylgeranyl pyrophosphate (GGPP) but not farnesyl pyrophosphate (FPP) nor cholesterol. Treatment with prenyltransferase inhibitors showed that chemoattractant responses were dependent on geranylgeranylation. Proteomic analysis of C15AlkOPP-prenylated proteins identified geranylgeranylated proteins involved in chemoattractant responses, including RHOA, RAC1, CDC42, and GNG2. Given the kinetic problems with initiating statin treatment after sepsis onset, prenyltransferases and geranylgeranylated proteins, such as RAC1 and GNG2, are promising interventional candidates for sepsis and critical inflammatory illness.