Harnessing conserved signaling and metabolic pathways to enhance the maturation of functional engineered tissues

Abstract

The development of induced-pluripotent stem cell (iPSC)-derived cell types offers promise for basic science, drug testing, disease modeling, personalized medicine, and translatable cell therapies across many tissue types. However, in practice many iPSC-derived cells have presented as immature in physiological function, and despite efforts to recapitulate adult maturity, most have yet to meet the necessary benchmarks for the intended tissues. Here, we summarize the available state of knowledge surrounding the physiological mechanisms underlying cell maturation in several key tissues. Common signaling consolidators, as well as potential synergies between critical signaling pathways are explored. Finally, current practices in physiologically relevant tissue engineering and experimental design are critically examined, with the goal of integrating greater decision paradigms and frameworks towards achieving efficient maturation strategies, which in turn may produce higher-valued iPSC-derived tissues.

Fig. 1. Common physiological trends in cell and tissue maturation.

As metabolically provided energy is diverted from proliferative activity to physiological function, cell complexity, and functional parameters are improved. This increasing specialization necessitates an investment of energy to manage cell size, structure, and specialized structures or organelles. The energetic outlay and continued flux for this expenditure is generally maintained by high-yield and efficient oxidative phosphorylation from lipids, short-chain fatty acids, carbohydrates, amino acids, lactate, and/or ketones, depending on the specific tissue and stage of maturation in question. Metabolic supply is provided by increased perfusion and spatial zonation, at which point the tissue can then exert its hallmark function. Image created using BioRender.com.

Fig. 2. Simplified visualization of common convergences between ubiquitous signaling pathways influencing tissue maturation.

Black arrows represent activation while red hashes represent inhibition; solid lines represent putatively direct interactions while dashed lines represent indirect effects (intermediates not shown or unknown). Image created using BioRender.com.

Fig. 3. Convergences between physical signaling and common consolidated pathways.

Black arrows represent activation while red hashes represent inhibition; solid lines represent putatively direct interactions while dashed lines represent indirect effects (intermediates not shown or unknown). Image created using BioRender.com.

Fig. 4. Interdependency of consolidating signal transduction pathways, and oscillatory signaling processes and second messengers coordinating tissue function, in introducing complexity when setting optimization metrics, prescribed signaling targets, or scoring paradigms.

a Opposing and aligned roles of Akt and AMPK in cell processes. b Oscillatory inputs (e.g., [Ca²⁺] or [cAMP]; top) can be decoded on an amplitude-dependent (left) or frequency-dependent (right) basis based on receiver process kinetics being slow or fast, respectively, lending further mutability to the physiological manifestation of a set of interdependent and multi-step signaling pathways. Reproduced with the express permission of the publisher and authors. c Simulated interactions between calcium and cAMP levels in a model of mutual enzymatic activation, based on active phospholipase Cβ (PLCβ) concentration and a set adenylate cyclase concentration of 0.17 µM; demonstrating interdependency of second messenger kinetics on their ultimate manifestation as an output response. Reproduced under a CC-BY license with express permission of the authors. d Sample visualization of an iterative High Dimensional, Differential Evolutionary (HD-DE) algorithm with successive generations outperforming each other on a normalized objective metric, with biological variability represented by temporary differences in performance between independent iterative runs that ultimately converge at highly-performing solution scores; this algorithm was used to optimize hematopoietic stem cell expansion medium efficacy. Reproduced under a CC-BY license with express permission of the authors.