Sabrina Jedlicka. Interactions of Neurons and Materials

Transcription

1 Sabrina Jedlicka Interactions of Neurons and Materials

2 Developmental Cell Biology

3 Some Perspective Stem cells: Undifferentiated cells that are capable of proliferation, self-maintenance and differentiation towards specific cell phenotypes These cells can be further classified as: ú ú ú ú Totipotent (all cells arise from small cluster of cells that a fertilized egg turns into) Pluripotent (all 3 germ layers) Multipotent (can differentiate into a small number of cells suitable to their existing location) And others (such as IPSCs)

4 How does this happen? Via a process known as signal transduction. Cells respond to a variety of signals ú ECM ú Morphogens ú Cytokines/Chemokines ú Hormones ú Growth Factors ú Mechanical Factors ú Etc.

5 In vivo vs. In vitro In vivo, cells respond to a number of stimuli at any given time. The process is coordinated and quite elegant In vitro, we are often unable to simulate this environment effectively

6 Traditional Approaches to Cell Differentiation Chemical Addition Cells Differentiate, but functionality is limited Petri Dish Pluripotent Cells Cell Differentiation Limited Commitment In Vivo Chemical, Mechanical, Material Cues Depending on Location Full Commitment Functional Maturation

7 How to grow neuronal cells in culture From proliferation to differentiation There is a subset of bioengineering that focuses on developing biomaterials for integration with neural systems, either in vivo orin vitro Used in development of cell models to understand disease Used in development of cell models for drug testing Used in developing therapies for damaged tissues

8 Cell-Material Interactions Neural Stem Cells Cellular Mechanotransduction Cellular Biomechanics Surface-Induced Chemotransduction

9 Definitions Cellular Mechanotransduction ú The mechanism by which cells convert mechanical signals in biochemical responses Cellular Mechanobiology ú Characterization of cell mechanics Cellular Surface Induced Chemotransduction ú The mechanism by which cells respond to surface-bound signals (such as ECM proteins)

10 Why does chemomechanotransduction matter? Cell Proliferation ú Disease States ú Propagation of sufficient cell numbers for therapeutics Cell Communication ú Force translation via cell-cell contacts ú Downstream biochemical signaling Cell Differentiation ú Development of useful cell-based models for research ú Differentiation of cells into more mature phenotypes for transplantation

11 Research History Mesenchymal stem cells differentiate based on substrate elasticity (Engler et al., 2006) Engler, A. J., Sen, S., Sweeney, H. L., & Discher, D. E. (2006). Matrix elasticity directs stem cell lineage specification. Cell, 126(4),

12 Our Interest: Neural Stem Cells Most research in NSC development is focused on soluble growth signals or ECM molecules However, NSCs are responsive to mechanical stimuli as well

13 C17.2 Neural Stem Cells Neuronal differentiation is controlled via serum withdrawal (starvation), which usually results in a homogeneous population of neurons But

14 Controlling Differentiation In vivo processes are highly coordinated and elegant. Some of the proteins involved in asymmetric division are known (Example: Numb), but some of their roles are not clearly defined However, in a lab setting, when you are trying to regrow neurons for therapeutic purposes you often start with stem cells in a petri dish, which does not have the elegant coordination of signals to trigger cell changes at the right time and place.

15 Goals: Enhancing Differentiation Controlling the chemomechanical environment may allow us to provide the right signals to stimulate NSCs to become postmitotic neurons of phenotype X for treatment of a certain disease. Alternatively, it will provide a means to produce new model system to study novel drugs And lots of other applications!

16 NSCs and Chemo-Mechanosensing How do material cues impact differentiation of NSCs?

17 Materials Design Mimic the extracellular environment during early corticogenesis Diverse Neuronal Population ECM Is Critical for Appropriate Cell Differentiation and Migration Laminin Fibronectin Collagen Lamellipodia formation and lamellipodia/filopodia extension Src FAK Cas Shc GRB2/mSos Cadherin containing cadherins junctions Cdc42 Cell polarity Rac PAK Jnk Rho Ras P1-3K Erk C-Fos/c -Jun FGF pathways Gene Transcription SCG10 Axonal guidance Neuronal cytoarchitecture

18 Material composition affects cell type diversity RGD/YIG/NID RGD/YIG/IKV/VSW More Neurons More Astrocytes *

19 Mechanical Influences Extent of C17.2 stem cell differentiation depends on the stiffness of the substrate Softer substrates promote differentiation into neurons and the formation of longer neurite extensions, as shown by analysis of the expression of neuron-specific β- tubulin III 140 Pa Pa

20 Some Surfaces lead to 100% neuronal populations

21 Proliferation and Neurogenesis The degree of cell proliferation is controlled in part by the degree of asymmetric cell division When a progenitor cell divides it can make any variety of cell combinations: ú ú ú ú Two progenitors One progenitor and one neuron One progenitor and one astrocyte Etc.

22 Differences in Division Type?

23 Results Asymmetric Division during Differentiation on Various Substrates A 0.8! During differentiation, number of asymmetric divisions is greater on glass over the soft surfaces. Fraction Asymmetric Division! 0.7! 0.6! 0.5! 0.4! 0.3! 0.2! 0.1! 0! B 140 Pa! 73 GPa (glass)! Collagen on glass! 100! % of Final Population that is Tuj1+! 90! 80! 70! 60! 50! 40! 30! 20! 10! 0! 140 Pa!! 73 GPa (glass)!!collagen on glass! on glass!

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25 Results Cells grown on softer surfaces form functional synapses (red: synaptophysin, green: Homer) Softer surfaces yield a more homogeneous, more mature population of neurons

26 Working Hypothesis Substrates are forcing cytoskeletal changes, altering the division dynamics, force transduction, and subsequent gene expression Day 10 Asymmetric Division Peaks Day 23 NSC Day 5 Cell Division Peaks Day 10 Nestin expression falls Day Most prominent morphological changes Tuj1 expression peaks CNTs are interacting with cytoskeleton, altering the division dynamics ** early redistribution of actin (i.e. mechanical remodeling!) CNTs are altering gene expression, but how?

27 Can we manipulate these processes from the inside-out? Nanomaterials

28 Nanomaterials Concentration Dependent Effect Useful for Imaging, Sensing, Etc. Long-term Impacts?

29 Single CNTs in cells

30 Nanomaterials Data Low conc High conc The presence of CNT increases the % of cells expressing β- tubulin III. Internal destabilization or oompliance changes? Fraction Neuronal Low Concentration Regular DNAc DNA RNAc RNA

31 Implications? Establishing an understanding of how mechanical influences (both macro and nano) change cell fate => new therapies and models

32 Much more work to be done

33 Questions?