The effects of progenitor and differentiated cells on ectopic calcification of engineered vascular tissues.

Ectopic vascular calcification associated with aging, diabetes mellitus, atherosclerosis, and chronic kidney disease is a considerable risk factor for cardiovascular events and death. Although vascular smooth muscle cells are primarily implicated in calcification, the role of progenitor cells is less known. In this study, we engineered tubular vascular tissues from embryonic multipotent mesenchymal progenitor cells either without differentiating or after differentiating them into smooth muscle cells and studied ectopic calcification through targeted gene analysis. Tissues derived from both differentiated and undifferentiated cells calcified in response to hyperphosphatemic inorganic phosphate (Pi) treatment suggesting that a single cell-type (progenitor cells or differentiated cells) may not be the sole cause of the process. We also demonstrated that Vitamin K, which is the matrix gla protein activator, had a protective role against calcification in engineered vascular tissues. Addition of partially-soluble elastin upregulated osteogenic marker genes suggesting a calcification process. Furthermore, partially-soluble elastin downregulated smooth muscle myosin heavy chain (Myh11) gene which is a late-stage differentiation marker. This latter point, in turn, suggests that SMC may be switching into a synthetic phenotype which is one feature of vascular calcification. Taken together, our approach presents a valuable tool to study ectopic calcification and associated gene expressions relevant to clinical therapeutic targets.

Comparative Studies of Fibrin-Based Engineered Vascular Tissues and Notch Signaling from Progenitor Cells.

The main impetus of vascular tissue engineering is clinical translation, but an equally appealing and impactful use of engineered vascular tissues is as preclinical testing platforms for studying vascular disease and developing therapeutic drugs and understanding of physiologically relevant vascular biology. Developing model engineered tissues will aid in narrowing the significant knowledge gaps in functional tissue formation, which is regulated by intricate cell signaling in a three-dimensional space. In this study, we fabricated tubular engineered vascular tissues using cross-linked fibrinogen as a scaffold and nondifferentiated embryonic rat vascular smooth muscle cell line (A10 cells) and mouse embryonic multipotent mesenchymal progenitor cell line (10T1/2 cells) as model vascular cells. Fibrin gel dimensional contraction kinetics study showed that A10 cells embedded in the gel were unable to significantly contract the tissue compared to fibrin-only gels because of their undifferentiated state. In contrast, 10T1/2 cells differentiated with TGF-ß1 to a vascular lineage were able to contract the tubular gel significantly owing to the contractile cytoskeletal stress fibers. Because of its vital role in vascular morphogenesis, tissue specification, and maturation, Notch signaling studies in engineered vascular tissues from A10 cells demonstrated cis-inhibition, whereas 10T1/2 cells activated Notch and its downstream targets Hes-1 and the smooth muscle α-actin genes. Taken together, this study showed that (i) contrary to the previously accepted notion, cell-type is important to gel contractions, and (ii) in engineered vascular tissues, Notch signaling is highly context-dependent, where cis-inhibition muted signal activation in A10 vascular cells, whereas Notch was fully activated in 10T1/2 cells. These findings may provide insights to fabricate functional vascular tissues.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine.

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

Monensin inhibits epidermal growth factor receptor trafficking and activation: synergistic cytotoxicity in combination with EGFR inhibitors.

Targeting the EGFR, with inhibitors such as erlotinib, represents a promising therapeutic option in advanced head and neck squamous cell carcinomas (HNSCC). However, they lack significant efficacy as single agents. Recently, we identified the ability of statins to induce synergistic cytotoxicity in HNSCC cells through targeting the activation and trafficking of the EGFR. However, in a phase I trial of rosuvastatin and erlotinib, statin-induced muscle pathology limited the usefulness of this approach. To overcome these toxicity limitations, we sought to uncover other potential combinations using a 1,200 compound screen of FDA-approved drugs. We identified monensin, a coccidial antibiotic, as synergistically enhancing the cytotoxicity of erlotinib in two cell line models of HNSCC, SCC9 and SCC25. Monensin treatment mimicked the inhibitory effects of statins on EGFR activation and downstream signaling. RNA-seq analysis of monensin-treated SCC25 cells demonstrated a wide array of cholesterol and lipid synthesis genes upregulated by this treatment similar to statin treatment. However, this pattern was not recapitulated in SCC9 cells as monensin specifically induced the expression of activation of transcription factor (ATF) 3, a key regulator of statin-induced apoptosis. This differential response was also demonstrated in monensin-treated ex vivo surgical tissues in which HMG-CoA reductase expression and ATF3 were either not induced, induced singly, or both induced together in a cohort of 10 patient samples, including four HNSCC. These results suggest the potential clinical utility of combining monensin with erlotinib in patients with HNSCC.

Lovastatin induces multiple stress pathways including LKB1/AMPK activation that regulate its cytotoxic effects in squamous cell carcinoma cells.

BACKGROUND: Cellular stress responses trigger signaling cascades that inhibit proliferation and protein translation to help alleviate the stress or if the stress cannot be overcome induce apoptosis. In recent studies, we demonstrated the ability of lovastatin, an inhibitor of mevalonate synthesis, to induce the Integrated Stress Response as well as inhibiting epidermal growth factor receptor (EGFR) activation. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we evaluated the effects of lovastatin on the activity of the LKB1/AMPK pathway that is activated upon cellular energy shortage and can interact with the above pathways. In the squamous cell carcinoma (SCC) cell lines SCC9 and SCC25, lovastatin treatment (1-25 µM, 24 hrs) induced LKB1 and AMPK activation similar to metformin (1-10 mM, 24 hrs), a known inducer of this pathway. Lovastatin treatment impaired mitochondrial function and also decreased cellular ADP/ATP ratios, common triggers of LKB1/AMPK activation. The cytotoxic effects of lovastatin were attenuated in LKB1 null MEFs indicating a role for this pathway in regulating lovastatin-induced cytotoxicity. Of clinical relevance, lovastatin induces synergistic cytotoxicity in combination with the EGFR inhibitor gefitinib. In LKB1 deficient (A549, HeLa) and expressing (SCC9, SCC25) cell lines, metformin enhanced gefitinib cytotoxicity only in LKB1 expressing cell lines while both groups showed synergistic cytotoxic effects with lovastatin treatments. Furthermore, the combination of lovastatin with gefitinib induced a potent apoptotic response without significant induction of autophagy that is often induced during metabolic stress inhibiting cell death. CONCLUSION/SIGNIFICANCE: Thus, targeting multiple metabolic stress pathways including the LKB1/AMPK pathway enhances lovastatin's ability to synergize with gefitinib in SCC cells.