# Mechanisms Regulating Vascular Homeostasis

> **NIH NIH R01** · DUKE UNIVERSITY · 2021 · $590,864

## Abstract

PROJECT SUMMARY
Regulation of normal endothelial cell (EC) function plays a critical role in vascular homeostasis and the
prevention of cardiovascular disease (CVD). Endothelial dysfunction in CVD is characterized by loss of
endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO). The Tie receptors and their ligands, the
angiopoietins (Ang), are important regulators of vascular homeostasis and the transition from EC quiescence
to "activation" and vascular remodeling. Whereas Ang-1/Tie2 signaling promotes EC survival and quiescence,
in part through activation of Akt and eNOS, the homologous Tie1 receptor has been shown to promote EC
activation, inflammation, and atherosclerosis. However, Tie1 is also required for Tie2-mediated angiogenesis,
and Tie1's overall functional effects appear to be context-dependent and linked, in part, to the presence of
inflammation. Unlike Tie2, Tie1 has no known activating ligands, therefore its signaling pathways and
mechanisms of action have been difficult to study and remain poorly understood. We identified a novel and
previously uncharacterized molecular scaffolding protein, Caskin2, as a Tie1-interacting protein. Although few
studies have specifically addressed Caskin2's function, it has been identified as a strong marker of ECs, and
numerous molecular studies have linked Caskin2 to phenotypes associated with defects in vascular
homeostasis. Importantly, our studies indicate that Caskin2 is a critical molecular link between Tie receptor
signaling, eNOS biology, and vascular homeostasis. Our preliminary studies in this proposal demonstrate that
Caskin2 is highly expressed in ECs in vitro and in vivo and that Caskin2 promotes EC quiescence and survival
in vitro. Caskin2 binding to Tie1 is disrupted by phosphorylation of T794 on Tie1, an event that is mediated by
PAK in a Rac-dependent manner and that is required for angiogenesis. Moreover, Caskin2 is required for Ang-
1/Tie2-mediated signaling through Akt, suggesting that Caskin2 integrates signals from both Tie1 and Tie2 to
regulate vascular homeostasis. Furthermore, Caskin2 binds eNOS and its activator calmodulin (CaM) and
increases eNOS expression and activity and is upregulated by fluid shear stress and by KLF2. Finally, we
show that Caskin2–/– mice have increased vascular permeability, atherosclerosis, pathological angiogenesis,
and are hypertensive, all disorders of vascular homeostasis characterized by abnormal eNOS signaling. Based
on these findings, we hypothesize that Caskin2 is a critical integrator of Tie receptor signaling that
regulates vascular homeostasis in part through eNOS activation. To test this hypothesis, the Specific
Aims of this proposal are to: 1) Determine the molecular mechanisms by which Caskin2 regulates Tie
receptor-mediated endothelial function and eNOS activity; 2) Determine the mechanisms by which Caskin2
responds to and senses changes in fluid shear stress to regulate EC phenotypes in vitro; and 3) Determine the
effects...

## Key facts

- **NIH application ID:** 10299286
- **Project number:** 1R01HL156009-01A1
- **Recipient organization:** DUKE UNIVERSITY
- **Principal Investigator:** Christopher D Kontos
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $590,864
- **Award type:** 1
- **Project period:** 2021-09-01 → 2025-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10299286

## Citation

> US National Institutes of Health, RePORTER application 10299286, Mechanisms Regulating Vascular Homeostasis (1R01HL156009-01A1). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10299286. Licensed CC0.

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