Differential Intrahepatic Phospholipid Zonation in Simple Steatosis and Nonalcoholic Steatohepatitis

Abstract

Nonalcoholic fatty liver disease (NAFLD) occurs frequently in a setting of obesity, dyslipidemia and insulin resistance, but the etiology of the disease, particularly the events favoring progression to nonalcoholic steatohepatitis (NASH) as opposed to simple steatosis (SS), are not fully understood. Based on known zonation patterns in protein, glucose and lipid metabolism, coupled with evidence that phosphatidylcholine may play a role in NASH pathogenesis, we hypothesized that phospholipid zonation exists in liver and that specific phospholipid abundance and distribution may be associated with histologic disease. A survey of normal hepatic protein expression profiles in the Human Protein Atlas revealed pronounced zonation of enzymes involved in lipid utilization and storage, particularly those facilitating phosphatidylcholine (PC) metabolism. Immunohistochemistry of obese normal, SS and NASH liver specimens with anti-phosphatidylethanomine N-methyltransferase (PEMT) antibodies showed a progressive decrease in the zonal distribution of this PC biosynthetic enzyme. Phospholipid quantitation by liquid chromatography mass spectrometry (LC-MS) in hepatic extracts of Class III obese patients with increasing NAFLD severity revealed that most PC species with 32, 34 and 36 carbons as well as total PC abundance was decreased with SS and NASH. Matrix assisted laser desorption ionization - imaging mass spectrometry (MALDI-IMS) imaging revealed strong zonal distributions for 32, 34 and 36 carbon PCs in controls (minimal histologic findings) and SS that was lost in NASH specimens. Specific lipid species such as PC 34∶1 and PC 36∶2 best illustrated this phenomenon. These findings suggest that phospholipid zonation may be associated with the presence of an intrahepatic proinflammatory phenotype and thus have broad implications in the etiopathogenesis of NASH.

Alcohol produces distinct hepatic lipidome and eicosanoid signature in lean and obese

“…PC depletion has been implicated in the pathogenesis of NAFLD (17,18,43,44). The current studies demonstrate that alcohol consumption in the background of obesity can lead to depletion of PC.…”

Pre-clinical and clinical investigations of metabolic zonation in liver diseases: The potential of microphysiology systems

“…Phosphatidylcholine metabolism through PMET is diminished and pan-zonal. 19 Although NASH patients have elevated serum bile acids and decreased lysophosphatidylcholine, the relationship between NASH and zone-specific functions remains largely unknown. 20 Mantena et al 21 found dysregulated oxygen gradient and mitochondrial effects in a high-fat diet NAFLD disease model in the mouse from which he postulates NASH and NAFLD alters the sinusoidal oxygen gradient so that zone 1 hepatocytes consume more oxygen but puts zone 2 and zone 3 hepatocytes into severe hypoxia ....................................................................................................................... in KO mice.…”

Differential Lipid Profiles in Experimental Steatohepatitis: Role for Imaging Mass Spectrometry as a Diagnostic Aid

“…For example, MALDI-IMS has been used to visualize the heterogeneous distribution of PC species in mouse brains [34], and effects of traumatic brain injury on the differential localization of PCs in rat brains [35]. Furthermore, MALDI-IMS detected alterations in phospholipid zonation in human livers with steatosis or nonalcoholic steatohepatitis (NASH) [36], and MALDI-TOF was used to measure serum lipidomic profiles in patients with NASH [37]. The present study examines the utility of MALDI-IMS for distinguishing glycerophospholipid profiles in experimental steatohepatitis produced in Long Evans rats by chronic ethanol, NNK or ethanol+NNK exposures.…”