# Fatty Acid Composition, at Equivalent Lipid Exposure, Dictates Human Macrophage Polarization via PPARγ Signaling

## TL;DR

The type of fatty acids in a mixture, not the total fat amount, influences how human macrophages become pro- or anti-inflammatory, with PPARγ playing a key role.

## Contribution

The study reveals that fatty acid composition, not total fat content, determines macrophage polarization via PPARγ signaling in humans.

## Key findings

- Palmitate-enriched lipid mixtures induce pro-inflammatory M1-like macrophage polarization through PPARγ and ER-stress signaling.
- Unsaturated fat-dominant mixtures promote anti-inflammatory M2-like macrophage profiles via PPARα and IRF4 upregulation.
- PPARγ acts as a context-dependent lipid sensor linking fatty acid composition to macrophage inflammatory programming.

## Abstract

What are the main findings?
Fatty acid composition, rather than total fat content, directs inflammatory polarization in primary human macrophages, with distinct effects on M1-like and M2-like phenotypes.Palmitate-enriched lipid ratios are associated with PPARγ induction and ER-stress signaling, coinciding with pro-inflammatory polarization, whereas unsaturated fat-dominant ratios preferentially enhance PPARα and IRF4 expression and favor anti-inflammatory macrophage profiles.

Fatty acid composition, rather than total fat content, directs inflammatory polarization in primary human macrophages, with distinct effects on M1-like and M2-like phenotypes.

Palmitate-enriched lipid ratios are associated with PPARγ induction and ER-stress signaling, coinciding with pro-inflammatory polarization, whereas unsaturated fat-dominant ratios preferentially enhance PPARα and IRF4 expression and favor anti-inflammatory macrophage profiles.

What are the implications of the main findings?
PPARγ functions as a context-dependent lipid sensor that links fatty acid composition to macrophage inflammatory programming in human systems.These findings highlight the nutritional and therapeutic relevance of fatty acid composition, particularly unsaturated fat-enriched lipid formulations, in shaping innate immune responses and inflammatory tone.

PPARγ functions as a context-dependent lipid sensor that links fatty acid composition to macrophage inflammatory programming in human systems.

These findings highlight the nutritional and therapeutic relevance of fatty acid composition, particularly unsaturated fat-enriched lipid formulations, in shaping innate immune responses and inflammatory tone.

Dietary fats are consumed as mixtures, yet it remains unclear whether fatty acid composition, independent of fat content, dictates human macrophage polarization. We compared two defined mixtures containing identical fatty acids (palmitic, oleic, and linoleic acids) in different ratios: a palmitate-enriched mixture (4:3:3) and an unsaturated fat-dominant mixture (2:4:4). In primary human monocyte-derived macrophages, palmitate enrichment increased CD14+CD11b+HLA-DR+ pro-inflammatory polarization, whereas the unsaturated fat-dominant mixture increased CD14+CD11b+CD163+ anti-inflammatory polarization. Mechanistic studies in THP-1-derived macrophages recapitulated these phenotype shifts and identified a reciprocal nuclear-receptor program: palmitate enrichment induced peroxisome proliferator-activated receptor gamma (PPARγ), together with ER-stress mediators EIF2AK3 and DDIT3, while the unsaturated fat-dominant mixture preferentially induced PPARα and IRF4. Pharmacologic modulation demonstrated functional dependence on PPARγ: GW9662 attenuated palmitate-driven M1-like polarization, whereas rosiglitazone disrupted the protective program under unsaturated fat-dominant conditions. These findings show that fatty acid composition, at equivalent total lipid concentration, is a dominant determinant of human macrophage inflammatory fate and highlight PPARγ as a context-dependent lipid sensor.