Effect of free fatty acids on TGF-β1 mediated fibrogenesis in hepatic stellate cells

Cover Story

Brown adipose tissue (BAT) is a specialized fat tissue that is rich in mitochondria and promotes non-shivering thermogenesis by expressing the uncoupling protein 1 (UCP1). Unlike white adipose tissue, it burns calories to produce heat and therefore plays a key role in energy regulation and controlling metabolic health. Increasing energy expenditure by BAT activation is an intriguing therapeutic approach to combat the overwhelming obesity pandemic, either alone or to complement the current pharmacotherapy that mainly addresses energy intake based on the incretin-mimetic poly-agonist class of drugs. With this in mind it is not surprising that a lot of research was conducted to understand the molecular underpinnings of BAT regulation specifically addressing environmental cues. Cold exposure is the most powerful inducer of BAT activation leading to the upregulation of thermogenic gene program and adrenergic receptor-mediated activation of lipolysis and metabolism. BAT activation also occurs post-prandially, especially after acute overfeeding, to trigger diet-induced thermogenesis. However, this compensatory component of energy-expenditure is impaired during chronic overfeeding, a phenomenon that was termed adaptive thermogenesis, and is believed to further drive weight gain and obesity.

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William De Nardo, Jacqueline Bayliss, Sheik Nadeem Elahee Doomun, Olivia Lee, ... Matthew J. Watt

Effect of free fatty acids on TGF-β1 mediated fibrogenesis in hepatic stellate cells

Abstract/objective

Metabolic associated steatotic liver disease (MASLD) is the most prevalent liver disorder and a major risk factor for hepatic fibrosis. Activated hepatic stellate cells (HSCs) are the primary source of collagen production in the liver, contributing to fibrosis. However, the mechanisms by which HSCs reprogram their metabolism to support sustained collagen production, particularly in a lipid-rich environment such as MASLD, remain inadequately understood. In this study, we investigated the effect of extracellular fatty acids on HSC substrate metabolism, HSC activation, and collagen synthesis.

Methods

Immortalized human HSCs (LX-2 cells) were cultured with or without transforming growth factor-beta 1 (TGF-β1) and varying concentrations of palmitate or oleate. Cellular lipid composition was assessed by mass spectrometry lipidomics. Fatty acid metabolism was assessed using radiometric techniques and isotopic labelling experiments using ¹³C-glucose or ¹³C-palmitate. HSC activation was assessed by measuring ACTA2, TGFB1, and COL1A1 mRNA levels and collagen secretion by ELISA.

Results

TGF-β1 reduced the abundance of many lipid types in LX-2 cells. Exogenous palmitate did not increase HSC activation, as determined by ACTA2, TGFB1, COL1A1 mRNA levels. Palmitate potentiated TGF-β1 induced collagen secretion but not in the presence of oleate. Palmitate reduced glucose incorporation into glycine in activated HSCs and induced a reciprocal increase in palmitate incorporation into glycine, most likely via carbons derived from TCA cycle intermediates. Pharmacological inhibition of fatty acid uptake reduced TGF-β1-mediated collagen secretion.

Conclusions

These results suggest that in activated HSCs, palmitate oxidation is reduced and that TCA cycle intermediates derived from palmitate are used as carbon sources for amino acid production that supports collagen synthesis and secretion.