Extracellular Matrix Remodeling and the Control of Branching Morphogenetic Programs.

Epithelial cells and endothelial cells initiate distinct branching morphogenetic programs during their coordinated invasion and proliferation into the interstitial compartment, a tissue comprised of mesenchymal stromal cells and extracellular matrix (ECM). While mammary gland development occurs in a specialized stromal environment dominated by adipocytes and fibroblasts, endothelial cell branching proceeds throughout all tissues in the absence of a specific stromal cell population. Nevertheless, both epithelial cells and endothelial cells engaged in morphogenetic responses have been posited to mobilize proteolytic enzymes to penetrate ECM barriers. However, transgenic mouse models have failed to identify required proteolytic effectors or uncover the mechanisms whereby proteolytic changes in tissue microenvironments regulate cell behavior. Herein, we characterize functional roles performed by the two dominant transmembrane proteinases expressed during epithelial and endothelial cell branching processes, the membrane-anchored matrix metalloproteinases, MT1-MMP and MT2-MMP. Using a series of transgenic mouse models, we identify new and unanticipated roles for MT1-MMP and MT2-MMP in mammary gland morphogenesis as well as angiogenesis. Tissue-specific targeting of MT1-MMP and MT2-MMP demonstrate that early mammary gland branching, which takes place within an immature ECM, proceeds independently of either proteinase. Instead, both proteinases play important, but diametrically opposed, roles in mammary gland adipocytes, where MT1-MMP stimulates adipogenesis and lipid metabolism, while MT2-MMP represses the development of thermogenic beige/brown adipocytes. In marked contrast, during the major phases of postnatal mammary gland development where a mature ECM is actively deposited, branching requires stromal cell-, rather than epithelial cell-, derived MT1-MMP, where the proteinase regulates branching by remodeling a periductal network of ECM macromolecules dominated by type I collagen. Endothelial cells also rely on MT1-MMP to direct branching, but unexpectedly, the proteinase also controls proliferative responses via a novel regulatory axis wherein pericellular proteolysis of the ECM governs the cytoskeletal-nuclear membrane interactions responsible for regulating transcriptional activity. Together, these data create new paradigms relevant to morphogenesis and tissue remodeling, as well as identify novel roles for membrane-anchored metalloproteinases in governing ECM proteolysis and associated transcriptional programs.PHDCellular and Molecular BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120758/1/tyfei_1.pd

Developmental ECM Sculpting: Laying It Down and Cutting It Up

In mammals, proteolytic remodeling of the embryonic extracellular matrix (ECM) controls morphogenesis, but the key players remain elusive. Two recent reports identify new roles for metalloproteinases belonging to the MT-MMP and ADAMTS families in branching morphogenesis and interdigital web regression

Classifying Medulloblastoma Subgroups Based on Small, Clinically Achievable Gene Sets

As treatment protocols for medulloblastoma (MB) are becoming subgroup-specific, means for reliably distinguishing between its subgroups are a timely need. Currently available methods include immunohistochemical stains, which are subjective and often inconclusive, and molecular techniques—e.g., NanoString, microarrays, or DNA methylation assays—which are time-consuming, expensive and not widely available. Quantitative PCR (qPCR) provides a good alternative for these methods, but the current NanoString panel which includes 22 genes is impractical for qPCR. Here, we applied machine-learning–based classifiers to extract reliable, concise gene sets for distinguishing between the four MB subgroups, and we compared the accuracy of these gene sets to that of the known NanoString 22-gene set. We validated our results using an independent microarray-based dataset of 92 samples of all four subgroups. In addition, we performed a qPCR validation on a cohort of 18 patients diagnosed with SHH, Group 3 and Group 4 MB. We found that the 22-gene set can be reduced to only six genes (IMPG2, NPR3, KHDRBS2, RBM24, WIF1, and EMX2) without compromising accuracy. The identified gene set is sufficiently small to make a qPCR-based MB subgroup classification easily accessible to clinicians, even in developing, poorly equipped countries

Modulation of cardiac macrophages by phosphatidylserine-presenting liposomes improves infarct repair

Herein we investigated a new strategy for the modulation of cardiac macrophages to a reparative state, at a predetermined time after myocardial infarction (MI), in aim to promote resolution of inflammation and elicit infarct repair. The strategy employed intravenous injections of phosphatidylserine (PS)-presenting liposomes, mimicking the anti-inflammatory effects of apoptotic cells. Following PS-liposome uptake by macrophages in vitro and in vivo, the cells secreted high levels of anti-inflammatory cytokines [transforming growth factor β (TGFβ) and interleukin 10 (IL-10)] and upregulated the expression of the mannose receptor—CD206, concomitant with downregulation of proinflammatory markers, such as tumor necrosis factor α (TNFα) and the surface marker CD86. In a rat model of acute MI, targeting of PS-presenting liposomes to infarct macrophages after injection via the femoral vein was demonstrated by magnetic resonance imaging (MRI). The treatment promoted angiogenesis, the preservation of small scars, and prevented ventricular dilatation and remodeling. This strategy represents a unique and accessible approach for myocardial infarct repair

E-cadherin cleavage by MT2-MMP regulates apical junctional signaling and epithelial homeostasis in the intestine

Cadherin-based intercellular adhesions are essential players in epithelial homeostasis, but their dynamic regulation during tissue morphogenesis and remodeling remain largely undefined. Herein, we characterize an unexpected role for the membrane-anchored metalloproteinase MT2-MMP in regulating epithelial cell quiescence. Following coimmunoprecipitation and mass spectrometry, the MT2-MMP cytosolic tail was found to interact with the zonula occludens protein-1 (ZO-1) at the apical junctions of polarized epithelial cells. Functionally, MT2-MMP localizes in the apical domain of epithelial cells where it cleaves E-cadherin and promotes epithelial cell accumulation, a phenotype observed in 2D polarized cells as well as 3D cysts. MT2-MMP-mediated cleavage subsequently disrupts apical E-cadherin-mediated cell quiescence resulting in; i) relaxed apical cortical tension favoring cell extrusion and ii) re-sorting of Src kinase activity to junctional complexes, thereby promoting proliferation. Physiologically, MT2-MMP lossof- function alters E-cadherin distribution leading to impaired 3D organoid formation by mouse colonic epithelial cells ex vivo and reduction of cell proliferation within intestinal crypts in vivo. Taken together, these studies identify an MT2-MMP/E-cadherin axis that functions as a novel regulator of epithelial cell homeostasis in vivo