Lipocalin 2 induces neuroinflammation and blood-brain barrier dysfunction through liver-brain axis in murine model of nonalcoholic steatohepatitis

Ayan Mondal,Dipro Bose,Punnag Saha,Prakash Nagarkatti,Saurabh Chatterjee,Ratanesh Seth,Muayad Albadrani,Mitzi Nagarkatti,Diana Kimono,Sutapa Sarkar

doi:10.1186/s12974-020-01876-4

Abstract

BackgroundRecent clinical and basic research implicated a strong correlation between NAFLD/NASH phenotypes with ectopic manifestations including neuroinflammation and neurodegeneration, but the mediators and critical pathways involved are not well understood. Lipocalin 2 (Lcn2) is one of the important mediators exclusively produced in the liver and circulation during NASH pathology.MethodsUsing murine model of NASH, we studied the role of Lcn2 as a potent mediator of neuroinflammation and neurodegeneration in NASH pathology via the liver-brain axis.ResultsResults showed that high circulatory Lcn2 activated 24p3R (Lipocalin2 receptor) in the brain and induced the release of high mobility group box 1 (HMGB1) preferably from brain cells. Released HMGB1 acted as a preferential ligand to toll-like receptor 4 (TLR4) and induced oxidative stress by activation of NOX-2 signaling involving activated p65 protein of the NF-κB complex. Further, the HMGB1-derived downstream signaling cascade activated NLRP3 inflammasome and release of proinflammatory cytokines IL-6 and IL-1β from brain cells. In addition, to advance our present understanding, in vitro studies were performed in primary brain endothelial cells where results showed high circulatory Lcn2 influenced HMGB1 secretion. Mechanistically, we also showed that elevated Lcn2 level in underlying NASH might be a likely cause for induction of blood-brain barrier dysfunction since the adipokine decreased the expression of tight junction protein Claudin 5 and caused subsequent elevation of pro-inflammatory cytokines IL-6 and IL-1β.ConclusionIn conclusion, the NASH-induced brain pathology might be because of increased Lcn2-induced release of HMGB1 and accompanying neuroinflammation.

Highlights

Recent clinical and basic research implicated a strong correlation between Nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) phenotypes with ectopic manifestations including neuroinflammation and neurodegeneration, but the mediators and critical pathways involved are not well understood
Using a murine model of NASH, we show that increased circulatory Lipocalin 2 (Lcn2) upregulates expression of Lcn2 receptor (24p3R) on brain cells and secretion of a damage associated molecular pattern protein (DAMP), a high mobility group box 1 (HMGB1) that subsequently induces oxidative stress and nod-like receptor protein 3 (NLRP3) inflammasome activation on brain cells
Immunohistochemistry with Lcn2 in frontal cortex showed significantly increased immunoreactivity in methionine and choline deficient diet (MCD) fed mouse group compared to CHOW diet, representing an upregulation of Lcn2 in brain in metabolic associated fatty liver disease (MAFLD) to NASH pathology (Fig. 1a, b)

Summary

Introduction

Recent clinical and basic research implicated a strong correlation between NAFLD/NASH phenotypes with ectopic manifestations including neuroinflammation and neurodegeneration, but the mediators and critical pathways involved are not well understood. Nonalcoholic fatty liver disease (NAFLD) or more recently reclassified as metabolic associated fatty liver disease (MAFLD) is a chronic liver disease that affects approximately 10–15% of US population and a significant number of the global population [1, 2]. According to the recent Centers for Disease Control and Prevention (CDC) reports, 90% of the obese population and 40–70% of the patients with T2DM in the USA are perceived to be suffering from MAFLD. Previous studies have described that MAFLD/NASH contributes to disease pathology in several ectopic disorders like type 2 diabetes (T2DM), cardiovascular disease (CVD), and chronic kidney disease (CKD) [4]. Researchers found evidence of neuroinflammatory disorders like Alzheimer’s disease (AD) with MAFLD/ NASH phenotypes. A recent study by Seo et al reported association of MAFLD with cognitive dysfunctions [6]. Despite the existence of data showing the association of neuroinflammatory pathology in MAFLD or NASH, identifying factors and mechanisms of the underlying neuronal inflammation in MAFLD or NASH has remained elusive

Results

Discussion

Conclusion