Abstract Body (Do not enter title and authors here): Background
Atherosclerosis is the chronic build-up of plaque in the intima of arteries. Fortilin is a ubiquitously expressed, multifunctional protein. Fortilin protects macrophages (MΦ) from apoptosis; is abundant in atherosclerotic intima and promotes atherogenesis, though the mechanism remains unclear.
Hypothesis
Fortilin in MΦ increases atherosclerotic lesions, enhances foam cell (FCs) formation, and polarizes MΦ to pro-inflammatory phenotype.
Methods
For whole animal experiments, mice with MΦ-specific fortilin knockout, overexpressing Cre transgene, under LysM enhancer/promoter control (fortilin^KO-MΦ), and in hypercholesterolemic (HC) background (Ldlr^-/-Apobec1^-/-) were generated (KO) and fed normal chow diet for 10 months. The extent of atherosclerosis in the aortae was ascertained by cross-sectional assays and imaging mass cytometry (IMC). For cellular studies, MΦ lacking fortilin from mice (fortilin^KO-MΦ) or THP1 MΦ(THP1^KO-fortilin) were incubated with oxidized LDL (oxLDL), and flow cytometry-based FC formation assay and cytokine profiling were performed.
Results
The median survival of fortilin^KO-MΦ and fortilin^WT-MΦ mice were 104.0 and 96.0 weeks, respectively (P=0.24). In the aortae, KO mice exhibited significantly lesser atherosclerotic lesion compared to wild-type (WT) mice (WT vs. KO=0.162 ± 0.056 vs. 0.109 ± 0.031, P=0.026) and lesser FCs (WT vs. KO=12.6 ± 2.2 vs. 2.7 ± 2.7 A.U., P=0.0013). IMC revealed that intima of KO mice contained fewer MΦ (WT vs. KO = 300 vs. 3439 cells/mm², P<0.0001) than WT mice. Compared to WT, infiltration of MΦ and other immune cells (T cells, B cells, dendritic cells) into atherosclerotic intima was reduced in KO mice. THP1^KO-fortilin displayed 95% (P<0.0001) decrease in FCs as compared to THP1^WT-fortilin, while fortilin’s presence increased secretion of pro-inflammatory cytokines, in whole animal and in cellular studies. Fortilin deficiencies in macrophage did not impact efferocytosis, migration, or phagocytosis.
Conclusion
MΦ lacking fortilin led to significantly (a) lesser atherosclerosis, (b) decreased MΦ cells, (c) decreased FC formation, and (d) reduced pro-inflammatory cytokine production in the atherosclerotic intima. Fortilin in MΦ is directionally pro-atherosclerotic and targeting fortilin may offer therapeutic strategies to mitigate plaque progression and instability. These findings underscore fortilin’s dual role in metabolic and immune pathways, positioning it as a critical node in atherosclerotic pathogenesis.