Systematic profiling of spatiotemporal tissue and cellular stiffness in the developing brain

Abstract

Accumulating evidence implicates the significance of the physical properties of the niche in influencing the behavior, growth and differentiation of stem cells. Among the physical properties, extracellular stiffness has been shown to have direct effects on fate determination in several cell types in vitro. However, little evidence exists concerning whether shifts in stiffness occur in vivo during tissue development. To address this question, we present a systematic strategy to evaluate the shift in stiffness in a developing tissue using the mouse embryonic cerebral cortex as an experimental model. We combined atomic force microscopy measurements of tissue and cellular stiffness with immunostaining of specific markers of neural differentiation to correlate the value of stiffness with the characteristic features of tissues and cells in the developing brain. We found that the stiffness of the ventricular and subventricular zones increases gradually during development. Furthermore, a peak in tissue stiffness appeared in the intermediate zone at E16.5. The stiffness of the cortical plate showed an initial increase but decreased at E18.5, although the cellular stiffness of neurons monotonically increased in association with the maturation of the microtubule cytoskeleton. These results indicate that tissue stiffness cannot be solely determined by the stiffness of the cells that constitute the tissue. Taken together, our method profiles the stiffness of living tissue and cells with defined characteristics and can therefore be utilized to further understand the role of stiffness as a physical factor that determines cell fate during the formation of the cerebral cortex and other tissues.

Tissue mechanics regulate brain development, homeostasis and disease

“…The biophysical properties and innate stiffness of niches within the brain are also likely to play a role in cell fate. A recent report noted a pattern of stiffness gradients in the embryonic brain, as measured using in situ atomic force microscopy (AFM) (Koser et al, 2016), and the SVZ specifically is known to stiffen gradually over the course of embryonic development (Iwashita et al, 2014), although the bulk elastic modulus of the brain does not appreciably change during development or postnatally (Majkut et al, 2013). Directly altering brain stiffness or blocking mechanotransduction during development results in aberrant axonal growth and migration (Koser et al, 2016), also implicating mechanical signals as regulators of this process.…”

The role of cell body density in ruminant retina mechanics assessed by atomic force and Brillouin microscopy

“…Stiffness gradients have been found in brain (2, 6–9), spinal cord (10), and retinal tissue (11). CNS tissue is characterized by a complex, non-linear, viscoelastic response to applied strain (relative sample deformation) or stress (force per unit area) (6–15).…”

Nanoengineering neural stem cells on biomimetic substrates using magnetofection technology

“…36 In particular, NSCs have been shown to alter their proliferation, migration and fate in response to stiffness changes [12][13][14][15] and this has led to speculation properties may indeed influence the maintenance of the different cerebral cortex layers, including the ventricular zone (VZ) and SVZ NSC niches. 37 We observed that, over the range of collagen concentrations used here, hydrogel stiffness increased with collagen concentration from ca. 34 to 350 Pa.…”

“…30 -3000 Pa). [37][38][39] However, our stiffness measurement at 0.6 mg/mL (ca. 43 Crucially, collagen is transparent and therefore facilitates live cell monitoring of intraconstruct cells using both phase and fluorescence imaging technologies.…”