Description of Research Expertise

Key words
Mechanobiology, microenvironment, ECM, integrin, cadherin, signal transduction, cytoskeleton, focal adhesions, matrix remodeling, cell cycle, proliferation, cyclin-dependent kinases, mouse modeling, cardiovascular biology.


Description of research:

We are interested in understanding how physiological and pathological changes in the extracellular matrix (ECM) affect tissue stiffness, the actin cytoskeleton, the composition of adhesion receptor signaling complexes, intracellular forces, and ultimately, cell proliferation. Our goal is to combine mechanistic analysis in culture with functional testing in mouse models. We are interested in normal control mechanisms and how these are subverted in disease.

We are currently working in the following general areas.

i) Effects of extracellular stiffness and intracellular tension on the cell cycle.
Most mammalian cells live in an elastic microenvironment; stiffening of the microenvironment occurs in several diseases and perturbs normal cellular function. The effects of matrix elasticity on cellular function are difficult to examine when cells are cultured on traditional rigid plastic or glass substrata that are irrelevant to in vivo microenvironments. We are using bioengineered substrata (ECM-coated hydrogels), which can mimic the elasticity of tissues that cells inhabit in vivo to assess the effects of substratum stiffness on the cell cycle. With this approach, we study the effect of changes in matrix stiffness on the spatial distribution of intracellular forces, focal adhesion composition, and adhesion receptor (integrin and cadherin) signaling. These studies have lead to the identification of specific focal adhesion components controlling stiffness-dependent cyclin D1 expression and microRNAs controlling the cdk inhibitor, p27kip1.

ii) In vivo mechanobiology.
Ultimately, the importance of biomechanics to cellular function must be documented in vivo. We are approaching this issue by examining adhesion receptors and signaling pathways that regulate matrix remodeling, tissue stiffness, and vascular smooth muscle cell (VSMC) proliferation during the response to injury. We invoke the injury response by gently denuding the endothelium in the femoral artery of mice. By comparing the degree of VSMC proliferation in wild-type mice and mice with knock-outs/knock-ins of integrin regulated signaling and cell cycle genes, we can test, in vivo, the importance of the integrin- and stiffness-regulated signaling events we detect in primary VSMCs cultured on hydrogels. Similar studies are exploring the proliferative effects of N-cadherin and its potential interactions with integrins. This work has strong biomedical relevance since damage to the endothelial lining of blood vessels and smooth muscle cell proliferation play critical roles in cardiovascular disease.

iii) New cardiovascular protective effects of HDL and apolipoprotein E (apoE).
We have shown that apoE and apoE-containing HDL inhibit cell cycle progression in VSMCs in vitro and in vivo by regulating the levels of p27kip1. Our newest data indicate that apoE and apoE-containing HDL also suppress the synthesis of ECM genes, and thereby control arterial stiffness. These effects on the ECM and arterial stiffness protect against atherosclerosis, in part by reducing monocyte adhesion to subendothelial ECM and macrophage abundance in lesions. Overall, our work in this area is identifying new effects of rare HDL subspecies that have to potential to protect against cardiovascular disease independent of the established HDL effect on cholesterol.

Lab members:

Yongho Bae, PhD
Paola Castagnino, PhD
Alexandra Cretu, PhD
Shulin Liu, PhD
Ziba Razinia, PhD
Keeley Mui, graduate student
Bernadette Hsu, graduate student
Beth Hawthorne, M.S.
Tina Xu, B.S.