Targeting the Lcn2/Lcn2R-Grb2 cascade ameliorates mitochondrial bioenergetic failure and neuronal death in hepatic encephalopathy.

Hepatic encephalopathy (HE) is a severe neuropsychiatric complication of liver failure characterized by a spectrum of cognitive and motor impairments. Lipocalin-2 (Lcn2) is a multifunctional secretory protein and inflammatory mediator predominantly released by glial cells in response to brain insults, whereas its receptor, Lcn2R, is expressed in cells. Nevertheless, the precise role of this Lcn2/Lcn2R axis in HE pathogenesis remains poorly understood. This study investigated the cellular mechanisms by which the Lcn2/Lcn2R axis triggers neurotoxicity in an azoxymethane-induced mouse model of HE and primary neuronal cultures. RNA sequencing and immunofluorescence identified Lcn2 as the most significantly upregulated gene in the hippocampus, with its receptor, Lcn2R, expressed in neurons. Mechanistically, Lcn2 binding to Lcn2R recruits Grb2 to activate the downstream MEK/ERK signaling pathway. This pathway upregulates pyruvate dehydrogenase kinase 1 (PDK1) and PDK3, leading to the phosphorylation and inactivation of pyruvate dehydrogenase (PDH). Consequently, mitochondrial respiration experiments revealed that Lcn2 significantly impairs mitochondrial energy metabolism by reducing ATP-linked respiration and coupling efficiency. In vitro silencing of Lcn2R or inhibition of MEK (U0126) and PDK (dichloroacetate; DCA) reversed these metabolic deficits and prevented neuronal death. Furthermore, in vivo intracerebroventricular administration of an Lcn2-neutralizing antibody successfully restored cerebral ATP levels and reduced neuronal apoptosis in HE mice. In conclusion, our findings demonstrate that the Lcn2/Lcn2R axis contributes to HE pathogenesis by activating Grb2-mediated MEK/ERK/PDK signaling, which impairs mitochondrial ATP synthesis and ultimately induces neuronal apoptosis, highlighting this pathway as a potential therapeutic target for HE.