MT1-MMP Regulates Mesenchymal Stem Cell Fate Decisions

描述（由申请人提供）：从发育到出生后，在骨髓室中发现的间充质基质/干细胞（MSC）亚群显示出分化为成骨细胞或脂肪细胞的能力。虽然体外改变MSC形状、细胞外基质（ECM）刚性或ECM维度都已显示出调节分化，但能够调节这些环境线索的MSC内在效应物的存在或身份仍不清楚。最近，我们鉴定了膜锚定的基质金属蛋白酶MT 1-MMP作为干细胞谱系定型和分化的MSC-内在调节剂-在体外以及体内（Dev Cell，25：402-416，2013）。这些研究表明，MT 1-MMP依赖的ECM重塑启动了一个？1整合素-Rho/ROCK信号级联，其控制关键MSC转录激活因子雅普和TAZ的活性。然而，MSC转录程序变化的分子机制尚未探索。在新的研究中，我们发现MT 1-MMP在调节MSC核结构、染色质组织和转录能力方面起着迄今为止意想不到的作用。我们进一步确定，ECM导向的信号向细胞核的MT 1-MMP依赖性转导需要细胞骨架、肌动球蛋白产生的机械张力和含有Klarsicht、ANC-1、Syne同源（KASH）结构域的细胞质蛋白之间的功能性相互作用，所述细胞质蛋白通过SUN蛋白家族的成员（即，所谓的核骨架和细胞骨架的接头; LINC复合物）。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与核区室联系起来，并控制MSC谱系定型和分化。因此，我们建议i）表征在MT 1-MMP依赖性谱系定型和分化期间细胞骨架和核结构重组对MSC转录活性的动力学，ii）定义3-D细胞周ECM的MT 1-MMP依赖性重塑作为MSC核结构和功能的上游调节剂经由nesprin-SUN信号传导轴的作用，和TAZ轴作为主要的机械转导系统，负责在MSC谱系定型和分化期间将ECM衍生的线索连接到核区室。由于几乎所有的干细胞都存在于动态重塑的ECM中，因此我们认为，本提案中概述的分子机制将对理解干细胞功能的调节以及生长和发育中以及衰老期间和影响核支架的遗传疾病中的谱系承诺产生广泛影响。

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.