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Adhesion molecule signaling is critical to human pluripotent stem cell (hPSC) survival, self-renewal, and differentiation. Thus, hPSCs are grown as clumps of cells on feeder cell layers or poorly defined extracellular matrices such as Matrigel. We sought to define a small molecule that would initiate adhesion-based signaling to serve as a basis for a defined substrate for hPSC culture. Soluble angiopoeitin-1 (Ang-1)-derived peptide QHREDGS added to defined serum-free media increased hPSC colony cell number and size during long- and short-term culture when grown on feeder cell layers or Matrigel, i.e. on standard substrates, without affecting hPSC morphology, growth rate or the ability to differentiate into multiple lineages both in vitro and in vivo. Importantly, QHREDGS treatment decreased hPSC apoptosis during routine passaging and single-cell dissociation. Mechanistically, the interaction of QHREDGS with β1-integrins increased expression of integrin-linked kinase (ILK), increased expression and activation of extracellular signal-regulated kinases 1/2 (ERK1/2), and decreased caspase-3/7 activity. QHREDGS immobilization to polyethylene glycol hydrogels significantly increased cell adhesion in a dose-dependent manner. We propose QHREDGS as a small molecule inhibitor of hPSC apoptosis and the basis of an affordable defined substrate for hPSC maintenance., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Induction of apoptosis by tensile forces is an important determinant of connective tissue destruction in osteoarthritis and periodontal diseases. We examined the role of molecular components of the unfolded protein response in force-induced apoptosis. Magnetic fields were used to apply tensile force through integrins to cultured fibroblasts bound with collagen-coated magnetite beads. Tensile force induced caspase 3 cleavage, DNA fragmentation, depolarization of mitochondria, and induction of CHOP10, all indicative of activation of apoptosis. Immunoblotting, immunocytochemistry, and release of Ca(2+) from the endoplasmic reticulum showed evidence for both physical and functional associations between bound beads and the endoplasmic reticulum. Force-induced apoptosis was not detected in PERK null cells, but reconstitution of wild-type PERK in PERK null cells restored the apoptotic response. Force-induced apoptosis did not require PKR, GCN2, eIF2alpha, or CHOP10. Furthermore, force more than 24 h did not activate other initiators of the unfolded protein response including IRE-1 and ATF6. However, force-induced activation of caspase 3 was dependent on caspase 9 but was independent of mitochondria. We conclude that force-induced apoptosis depends on a novel function of PERK that occurs in addition to its canonical role in the unfolded protein response.