UC Irvine

Macrophages are innate immune cells that respond to pathogens in our body with inflammatory activation that brings about their destruction and removal. Additionally, macrophages can also play critical roles in tissue healing that follows inflammation. While many studies describe the effects of biochemical cues on macrophage inflammatory activation, the effects of biomechanical cues have not been well explained mechanistically. This dissertation aims to describe epigenetic mechanisms that empower macrophage mechanomodulation to guide inflammatory activation. Chapter 1 describes the mechanomodulatory effects of biomaterials used as negative pressure wound therapy wound dressings. We find that wound dressings that are non-adhesive suppress macrophage inflammatory activation. Chapter 2 describes the effects of biophysical cues that enable macrophage elongation. Using microcontact printing to facilitate macrophage elongation, we observe inflammatory downregulation, and concomitant reduction in histone 3 acetylation. Gene correlation analysis of high throughput gene expression data suggested the influence of the adhesome protein Src in mediating the cell elongation induced suppression of histone acetylation. This observation was verified by Src genetic knockdown and pharmacological inhibition, which both resulted in reduced histone 3 acetylation. In addition, Src activation phosphorylates and suppresses PKCδ, in turn a suppressor of the prominent histone acetyltransferase p300. Probing the mechanism further, we find that Src activation that happens in macrophages exposed to lipopolysaccharide (LPS)/interferon gamma (IFNγ), is curtailed in micropatterned macrophages, leading to inflammatory downregulation through deficient p300 HAT activity and subsequent histone 3 hypoacetylation. Chapter 3 describes the inflammatory effects of the mechanosensitive transcriptional coactivators Yes associated protein (YAP), and Transcriptional Coactivator With PDZ-Binding Motif (TAZ/WWTR1) that is caused by their interplay with the histone acetylation reader BRD4. We find all three proteins colocalize in the same immunocomplexes, and the shRNA-mediated knockdown of these three genes results in a significantly overlapping subset of differentially expressed genes. Upregulation of YAP/TAZ activity by overexpressing their respective constitutively active forms (YAP-5SA and TAZ-S89A) results in increased inflammation that can be offset by addition of BRD4 inhibitors (BETi). We also find that constitutive activity of YAP/TAZ results in increased oxLDL uptake, an event that is closely linked to atherogenesis. oxLDL uptake in macrophages was offset by either YAP, TAZ or BRD4 knockdown using shRNA, or using BETi treatment. Finally, we find that BETi drug treatment is atheroprotective in AAV9-D377Y-mPCSK9 mice that were fed with high fat diet (HFD) and functions by suppressing YAP/TAZ targets like CD36 and OLR1, both of which are oxLDL uptake receptors in macrophages.