MT1-MMP Regulates Mesenchymal Stem Cell Fate Decisions

描述（由申请人提供）：从发育到出生后，骨髓腔室中发现的间充质基质/干细胞（MSCs）亚群显示出分化成成骨细胞或脂肪细胞的能力。虽然改变间充质干细胞形状、细胞外基质（ECM）刚性或体外ECM维度都被证明可以调节分化，但能够调节三种环境信号的间充质干细胞内在效应物的存在或身份仍不清楚。最近，我们发现膜锚定基质金属蛋白酶，MT1-MMP，作为干细胞谱系承诺和分化的内在调节因子-在体外和体内（Dev cell, 25:402-416, 2013）。这些研究表明，mt1 - mmp依赖性的ECM重塑启动了一个？1整合素- rho /ROCK信号级联控制关键MSC转录激活因子YAP和TAZ的活性。然而，MSC转录程序变化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。我们进一步确定，mt1 - mmp依赖的ecm定向信号转导到细胞核需要细胞骨架、肌动球蛋白产生的机械张力和含有Klarsicht、ac -1、Syne同源（KASH）结构域的细胞质蛋白之间的功能相互作用，这些蛋白通过SUN蛋白家族成员（即所谓的核骨架和细胞骨架连接物；LINC复合物）将信号传递到富含层粘连蛋白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与核室联系起来，并控制MSC谱系的承诺和分化。因此，我们提出i)表征MT1-MMP依赖性谱系承诺和分化过程中细胞骨架和核结构重组对MSC转录活性的动态影响；ii)通过nesprinn - sun信号轴确定mt1 - mmp依赖性3-D细胞周围ECM重构作为MSC核结构和功能的上游调节剂的作用；iii)确定LINC复合物/层粘连蛋白A-YAP/TAZ轴是在MSC谱系承诺和分化过程中负责将ECM衍生线索连接到核室的主要机械转导系统。由于几乎所有的干细胞都存在于动态重塑的ECM中，我们假设本提案中概述的分子机制将对理解干细胞功能和谱系在生长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.