A game of two halves: inconsistent renal allograft function in two recipients of a split horseshoe kidney

International Urology and Nephrology -     

Substrate topography and size determine the fate of human embryonic stem cells to neuronal or glial lineage

Efficient derivation of neural cells from human embryonic stem cells (hESCs) remains an unmet need for the treatment of neurological disorders. The limiting factors for current methods include being labor-intensive, time-consuming and expensive. In this study, we hypothesize that the substrate topography, with optimal geometry and dimension, can modulate the neural fate of hESCs and enhance the efficiency of differentiation. A multi-architectural chip (MARC) containing fields of topographies varying in geometry and dimension was developed to facilitate high-throughput analysis of topography-induced neural differentiation in vitro. The hESCs were subjected to “direct differentiation”, in which small clumps of undifferentiated hESCs were cultured directly without going through the stage of embryoid body formation, on the MARC with N2 and B27 supplements for 7 days. The gene and protein expression analysis indicated that the anisotropic patterns like gratings promoted neuronal differentiation of hESCs while the isotropic patterns like pillars and wells promoted the glial differentiation of hESCs. This study showed that optimal combination of topography and biochemical cues could shorten the differentiation period and allowed derivation of neurons bearing longer neurites that were aligned along the grating axis. The MARC platform would enable high-throughput screening of topographical substrates that could maximize the efficiency of neuronal differentiation from pluripotent stem cells.     

Extending neurites sense the depth of the underlying topography during neuronal differentiation and contact guidance

The topography of the extracellular microenvironment influences cell morphology, provides conduct guidance and directs cell differentiation. Aspect ratio and dimension of topography have been shown to affect cell behaviours, but the ability and mechanism of depth-sensing is not clearly understood. We showed that murine neural progenitor cells (mNPCs) can sense the depth of the micro-gratings. Neurite elongation, alignment and neuronal differentiation were observed to increase with grating depth. We proposed a mechanism for depth-sensing by growing neurites: filopodial adhesion in the growth cones favour elongation but the bending rigidity of the neurite cytoskeleton resists it. Thus, perpendicular extension on deeper grooves is unfavourable as neurites need to bend over a larger angle. A quantitative model was developed and its prediction of neurite growth on gratings fit well with the experimental data. The results indicated that mNPC fate can be directed by appropriately designed patterned surfaces.