Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2023)

Duchenne muscular dystrophy (DMD) is one of the most common inherited, lethal childhood diseases. This X-linked recessive disorder is often caused by mutations in the DMD gene that leads to loss of functional dystrophin protein and results in myofibers that are susceptible to membrane rupture. Sarcolemmal fragility leads to chronic cycles of muscle degeneration and regeneration and a subsequent reprogramming of the muscle niche that includes unresolved inflammation, defective muscle stem cell activity, aberrant pathological fibrosis, intramuscular adipose tissue (IMAT) accumulation and ultimately failed regeneration. Our lab has shown that osteopontin (SPP1) is a critical regulator of DMD disease progression that links many of these processes through its complex biology. SPP1 is multifunctional matricelluar protein, encoded by the Spp1 gene, that is post-translationally modified in many ways, expressed by a host of different cells in the muscle niche and can bind to a plethora of different receptors. This complexity can greatly impact how SPP1 acts on target cells and the signaling cascades that result in DMD disease progression. In this dissertation, we utilized single cell RNA sequencing to unbiasedly explore how two cell-specific sources of SPP1, macrophage-derived and muscle stem cell-derived, affect cell-cell interactions in dystrophic muscle.Here we show that macrophage-derived SPP1 is an autocrine regulator of macrophage TGFβ1. We identified two novel adipogenically primed stromal cell populations that are regulated by macrophage-derived TGFβ and contribute to IMAT. Our work established a link between macrophage-derived SPP1, reduced macrophage-derived TGFβ and ectopic fatty infiltration that is a hallmark of progressive DMD. Additionally, we showed that muscle stem cell (MuSC)-specific SPP1 has an autocrine inhibitory effect on MuSC stemness and positive effect on the fibrotic and inflammatory phenotype of MuSCs. Endothelial cells greatly expand in the MuSC Spp1 cKO showing a pro-angiogenic, anti-inflammatory state. We hypothesize that MuSC-derived SPP1 crosstalks with endothelial cells (ECs), leading to reduced EC expansion and an anti-angiogenic, pro-inflammatory, activated state. Furthermore, we provide evidence that this MuSC-EC regulatory axis affects macrophage phenotype. Altogether, this work advances knowledge of cell-specific SPP1 biology that drives DMD disease progression.

    Cover page: The Effects of Macrophage and Muscle Stem Cell-Specific Spp1 on Cell-Cell Interactions in Dystrophic Muscle
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2018)
    The cellular and mechanistic bases underlying endothelial regeneration of adult large vessels have proven challenging to study. Using a reproducible in vivo aortic endothelial injury model, we characterized cellular dynamics underlying the regenerative process through a combination of multi-color lineage tracing, parabiosis, and single-cell transcriptomics. We found that regeneration is a biphasic process driven by distinct populations arising from differentiated endothelial cells. The majority of cells immediately adjacent to the injury site re-enter the cell cycle during the initial damage response, with a second phase driven by a highly proliferative subpopulation. Endothelial regeneration requires activation of stress response genes including Atf3, and aged aortas compromised in their reparative capacity express less Atf3. Deletion of Atf3 reduced endothelial proliferation and compromised the regeneration. These findings provide important insights into cellular dynamics and mechanisms that drive responses to large vessel injury.
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2017)
      Endothelial cells transduce mechanical forces from blood flow into intracellular signals required for vascular homeostasis. Here we show that endothelial NOTCH1 is responsive to shear stress, and is necessary for the maintenance of junctional integrity, cell elongation, and suppression of proliferation, phenotypes induced by laminar shear stress. NOTCH1 receptor localizes downstream of flow and canonical NOTCH signaling scales with the magnitude of fluid shear stress. Reduction of NOTCH1 destabilizes cellular junctions and triggers endothelial proliferation. NOTCH1 suppression results in changes in expression of genes involved in the regulation of intracellular calcium and proliferation, and preventing the increase of calcium signaling rescues the cell-cell junctional defects. Furthermore, loss of Notch1 in adult endothelium increases hypercholesterolemia-induced atherosclerosis in the descending aorta. We propose that NOTCH1 is atheroprotective and acts as a mechanosensor in adult arteries, where it integrates responses to laminar shear stress and regulates junctional integrity through modulation of calcium signaling.
        Cover page: NOTCH1 is a mechanosensor in adult arteries.
        Top