Figure Legends
Fig. 1. Molecular mechanisms of mechanotransduction in stem
cells. Mechanotransduction describes the ability of cells to sense
mechanical forces and translate them into biochemical reactions for
signal transduction and biological responses. When external forces, such
as fluid shear stress, are applied to cells, these forces are
transferred from the ECM to the cell, propagating from the outside into
the cell. Integrins are a family of transmembrane receptors connecting
the cytoskeleton to the ECM. They are also known to initiate cytosolic
signaling upon binding to extracellular ligands (outside-in signaling)
as well have their binding affinity regulated intracellularly
(inside-out signaling). Several mechanosensor proteins, including
mechanosensing ion channels, cell-substrate and cell-cell junctional
complexes, and cytoskeleton-associated complexes, have been identified
in stem cells. Arrows and bars represent the net result of a signaling
pathway. Abbreviations used: ECM, extracellular matrix; RhoA, Rho
kinase; ROCK, Rho-associated protein kinase; LINC, linker of
nucleoskeleton and cytoskeleton.
Fig. 2. Understanding the internal and external
variability-generated intrinsic disorder in stem cell bioprocess based
on mechanobiological considerations. The cell responses to internal and
external forces are represented by the time-related phenomena in
biological processes; time-dependency, time-delay, tardive, and
uncertainty. These may lead to cellular bioprocess variability, the
so-called intrinsic disorder that affects bioprocess efficiency.
Fig. 3. A simplified view of mechanosensing and
mechanotransduction signaling pathways for regulating stem cell
homeostasis. Cellular behavior is affected by mechanical forces through
the process of mechanotransduction, in which mechanical stimuli from
their extracellular environment or cell-generated forces are converted
into a set of biochemical reactions and a cellular response. We
categorized the “intrinsic cellular processes” as “trigger,”
“effector,” and “memorizer” key factors involved in
mechanotransduction. The actin-myosin cytoskeleton is defined as the
“integrator” and “organizer” of mechanical and biochemical signaling
inputs in these processes. Arrows and bars represent the net result of a
signaling pathway. Arrows and bars represent the net result of a
signaling pathway. Abbreviations used: RhoA, Rho kinase; MLC-P,
phosphorylated myosin II regulatory light chain; MLC-P, myosin light
chain phosphatase; MLCK, myosin light chain kinase.
Fig. 4. Development of criteria and indicators applicable to
the study of stem cell bioprocess effectiveness based on
mechanobiological mechanisms. We propose new indicators to assess the
cell status associated with cell behavior-driven epigenetic memory
formation in human induced pluripotent stem cell (hiPSC) culture, as a
case study. The acquired memories are transformed from a short-term
memory into a long-term memory in transition between exponential and
long-term stationary phases. The relationship between the indicators in
the same category was used to determine the cell state and
differentiation potential. The combination and integration of
qualitative and quantitative methods can be used to enhance stem cell
bioprocess optimization without compromising the product quality.
Fig. 5. Potential strategies and practical considerations to
stem cell bioprocess optimization with the conceptual framework based on
mechanobiological mechanisms. We propose a new conceptual framework that
systematically links three dimensions: inputs, outputs, and the
associated system level outcomes of bioprocess effectiveness. Based on
the dynamic relationship between the key factors (trigger, effector, and
memorizer) affecting the formation of epigenetic memory (sensory,
short-term, and long-term), the determination of the boundary conditions
of applied mechanical forces is important to enhance cell quality and
process robustness. The application of the conceptual frameworks can
apply an important approach that facilitate movement to understand,
predict, and control the intrinsic disorder in stem cell
bioprocessing. Finally, this allows that the output of the design
process, including a quality control plan, a bioprocessing plane, and a
strategy for facilities, validation, and other requirements.