MT1-MMP Regulates Mesenchymal Stem Cell Fate Decisions

描述(申请人提供)：从发育到出生后，在骨髓室中发现的间充质基质/干细胞(MSCs)亚群显示出分化为成骨细胞或脂肪细胞的能力。虽然在体外改变MSC的形状、细胞外基质(ECM)的硬度或ECM的维度都被证明可以调节分化，但MSC内在效应器的存在-或身份-能够调节这些环境信号仍不清楚。最近，我们在体外和体内都发现了膜锚定的基质金属蛋白酶MT1-MMPs，它是干细胞定向和分化的MSC内源性调节因子(Dev Cell，25：402-416,2013)。这些研究表明，依赖于MT1-MMPs的ECM重塑启动了1整合素-Rho/ROCK信号级联反应，从而控制了关键的MSC转录激活因子YAP和TAZ的活性。然而，MSC转录程序变化背后的分子机制仍未被探索。在新的研究中，我们发现MT1-MMP在调节MSC的核结构、染色质组织和转录能力方面发挥了迄今为止意想不到的作用。我们进一步证实，依赖于MT1-MMPs的ECM定向信号到细胞核的转导需要细胞骨架、由肌球蛋白产生的机械张力与含有Klarsicht、ANC-1、Syne Homology(KASH)结构域的细胞质蛋白之间的功能相互作用，这些细胞质蛋白通过SUN蛋白家族(即所谓的核骨架和细胞骨架的连接物；LINC复合体)将信号传递到富含lamin A的核支架。这些初步发现概述了一种新的MSC机械转导程序，该程序将3-D ECM连接到核间室，并控制MSC的谱系承诺和分化。因此，我们建议：1)研究MT1-基质金属蛋白酶依赖的细胞骨架和核结构重组对MSC转录活性的影响；2)确定MT1-基质金属基质依赖的3-D细胞周ECM重塑是通过Nesprin-SUN信号轴上游调节MSC核结构和功能的作用；3)确定LINC复合体/lamin A-YAP/TAZ轴是主要的机械转导系统，负责在MSC谱系承诺和分化过程中将ECM来源的信号连接到核室。由于几乎所有干细胞都驻留在动态重塑的ECM中，我们假设这一提议中概述的分子机制将对理解干细胞功能和谱系承诺在生长和发育以及衰老和影响核支架的遗传疾病中的调节具有广泛的意义。

DESCRIPTION (provided by applicant): From development through postnatal life, a subset of mesenchymal stromal/stem cells (MSCs) found in the bone marrow compartment, display an ability to differentiate into osteoblasts or adipocytes. While altering MSC shape, extracellular matrix (ECM) rigidity or ECM dimensionality in vitro have all been shown to modulate differentiation, the existence - or identity - of MSC-intrinsic effectors capable of regulating thee environmental cues has remained unclear. Recently, we identified the membrane- anchored matrix metalloproteinase, MT1-MMP, as an MSC-intrinsic regulator of stem cell lineage commitment and differentiation - in vitro as well as in vivo (Dev Cell, 25:402-416, 2013). These studies demonstrated that MT1-MMP-dependent remodeling of the ECM initiated a ?1 integrin-Rho/ROCK signaling cascade that controlled the activity of the key MSC transcriptional activators, YAP and TAZ. However, the molecular mechanisms underlying the changes in MSC transcriptional programs remained unexplored. In new studies, we find that MT1-MMP plays a heretofore unexpected role in modulating MSC nuclear architecture, chromatin organization and transcriptional competence. We further establish that the MT1-MMP-dependent transduction of ECM-directed signals to the nucleus requires functional interactions between the cytoskeleton, actomyosin-generated mechanical tension and Klarsicht, ANC-1, Syne homology (KASH) domain-containing cytoplasmic proteins that transmit signals to the lamin A-rich nuclear scaffold via members of the SUN protein family (i.e., the so-called linker of nucleoskeleton and cytoskeleton; LINC complex). These preliminary findings outline a novel MSC mechanotransduction program that links the 3-D ECM to the nuclear compartment and governs MSC lineage commitment and differentiation. Thus, we propose to i) characterize the dynamics of cytoskeletal and nuclear architecture reorganization on MSC transcriptional activity during MT1-MMP- dependent lineage commitment and differentiation, ii) define the role of MT1-MMP-dependent remodeling of the 3-D pericellular ECM as the upstream regulator of MSC nuclear architecture and function via the nesprin-SUN signaling axis and iii) identify the LINC complex/lamin A-YAP/TAZ axis as the dominant mechanotransduction system responsible for linking ECM-derived cues to the nuclear compartment during MSC lineage commitment and differentiation. As virtually all stem cells reside within a dynamically remodeled ECM, we posit that the molecular mechanisms outlined in this proposal will have broad implications for understanding the regulation of stem cell function and lineage commitment in growth and development as well as during aging and in genetic disorders affecting the nuclear scaffolding.