Substrate Stiffness Modulates Renal Progenitor Cell Properties via a ROCK-Mediated Mechanotransduction Mechanism

Role of biophysics and mechanobiology in podocyte physiology

Podocytes form the backbone of the glomerular filtration barrier and are exposed to various mechanical forces throughout the lifetime of an individual. The highly dynamic biomechanical environment of the glomerular capillaries greatly influences the cell biology of podocytes and their pathophysiology. Throughout the past two decades, a holistic picture of podocyte cell biology has emerged, highlighting mechanobiological signalling pathways, cytoskeletal dynamics and cellular adhesion as key determinants of biomechanical resilience in podocytes. This biomechanical resilience is essential for the physiological function of podocytes, including the formation and maintenance of the glomerular filtration barrier. Podocytes integrate diverse biomechanical stimuli from their environment and adapt their biophysical properties accordingly. However, perturbations in biomechanical cues or the underlying podocyte mechanobiology can lead to glomerular dysfunction with severe clinical consequences, including proteinuria and glomerulosclerosis. As our mechanistic understanding of podocyte mechanobiology and its role in the pathogenesis of glomerular disease increases, new targets for podocyte-specific therapeutics will emerge. Treating glomerular diseases by targeting podocyte mechanobiology might improve therapeutic precision and efficacy, with potential to reduce the burden of chronic kidney disease on individuals and health-care systems alike.

Decellularized kidney extracellular matrix-based hydrogels for renal tissue engineering

Kidney regeneration is hindered by the limited pool of intrinsic reparative cells. Advanced therapies targeting renal regeneration have the potential to alleviate the clinical and financial burdens associated with kidney disease. Delivery systems for cells, extracellular vesicles, or growth factors aimed at enhancing regeneration can benefit from vehicles enabling targeted delivery and controlled release. Hydrogels, optimized to carry biological cargo while promoting regeneration, have emerged as promising candidates for this purpose. This study aims to develop a hydrogel from decellularized kidney extracellular matrix (DKECM) and explore its biocompatibility as a biomaterial for renal regeneration. The resulting hydrogel crosslinks with temperature and exhibits a high concentration of extracellular matrix. The decellularization process efficiently removes detergent residues, yielding a pathogen-free biomaterial that is non-hemolytic and devoid of α-gal epitope. Upon interaction with macrophages, the hydrogel induces differentiation into both pro-inflammatory and anti-inflammatory phenotypes, suggesting an adequate balance to promote biomaterial functionality in vivo. Renal progenitor cells encapsulated in the DKECM hydrogel demonstrate higher viability and proliferation than in commercial collagen-I hydrogels, while also expressing tubular cells and podocyte markers in long-term culture. Overall, the injectable biomaterial derived from porcine DKECM is anticipated to elicit minimal host reaction while fostering progenitor cell bioactivity, offering a potential avenue for enhancing renal regeneration in clinical settings. STATEMENT OF SIGNIFICANCE: The quest to improve treatments for kidney disease is crucial, given the challenges faced by patients on dialysis or waiting for transplants. Exciting new therapies combining biomaterials with cells can revolutionize kidney repair. In this study, researchers created a hydrogel from pig kidney. This gel could be used to deliver cells and other substances that help in kidney regeneration. Despite coming from pigs, it's safe for use in humans, with no harmful substances and reduced risk of immune reactions. Importantly, it promotes a balanced healing response in the body. This research not only advances our knowledge of kidney repair but also offers hope for more effective treatments for kidney diseases.

Modeled microgravity unravels the roles of mechanical forces in renal progenitor cell physiology

BACKGROUND

The glomerulus is a highly complex system, composed of different interdependent cell types that are subjected to various mechanical stimuli. These stimuli regulate multiple cellular functions, and changes in these functions may contribute to tissue damage and disease progression. To date, our understanding of the mechanobiology of glomerular cells is limited, with most research focused on the adaptive response of podocytes. However, it is crucial to recognize the interdependence between podocytes and parietal epithelial cells, in particular with the progenitor subset, as it plays a critical role in various manifestations of glomerular diseases. This highlights the necessity to implement the analysis of the effects of mechanical stress on renal progenitor cells.

METHODS

Microgravity, modeled by Rotary Cell Culture System, has been employed as a system to investigate how renal progenitor cells respond to alterations in the mechanical cues within their microenvironment. Changes in cell phenotype, cytoskeleton organization, cell proliferation, cell adhesion and cell capacity for differentiation into podocytes were analyzed.

RESULTS

In modeled microgravity conditions, renal progenitor cells showed altered cytoskeleton and focal adhesion organization associated with a reduction in cell proliferation, cell adhesion and spreading capacity. Moreover, mechanical forces appeared to be essential for renal progenitor differentiation into podocytes. Indeed, when renal progenitors were exposed to a differentiative agent in modeled microgravity conditions, it impaired the acquisition of a complex podocyte-like F-actin cytoskeleton and the expression of specific podocyte markers, such as nephrin and nestin. Importantly, the stabilization of the cytoskeleton with a calcineurin inhibitor, cyclosporine A, rescued the differentiation of renal progenitor cells into podocytes in modeled microgravity conditions.

CONCLUSIONS

Alterations in the organization of the renal progenitor cytoskeleton due to unloading conditions negatively affect the regenerative capacity of these cells. These findings strengthen the concept that changes in mechanical cues can initiate a pathophysiological process in the glomerulus, not only altering podocyte actin cytoskeleton, but also extending the detrimental effect to the renal progenitor population. This underscores the significance of the cytoskeleton as a druggable target for kidney diseases.

Electroconductive Collagen-Carbon Nanodots Nanocomposite Elicits Neurite Outgrowth, Supports Neurogenic Differentiation and Accelerates Electrophysiological Maturation of Neural Progenitor Spheroids

Neuronal disorders are characterized by the loss of functional neurons and disrupted neuroanatomical connectivity, severely impacting the quality of life of patients. This study investigates a novel electroconductive nanocomposite consisting of glycine-derived carbon nanodots (GlyCNDs) incorporated into a collagen matrix and validates its beneficial physicochemical and electro-active cueing to relevant cells. To this end, this work employs mouse induced pluripotent stem cell (iPSC)-derived neural progenitor (NP) spheroids. The findings reveal that the nanocomposite markedly augmented neuronal differentiation in NP spheroids and stimulate neuritogenesis. In addition, this work demonstrates that the biomaterial-driven enhancements of the cellular response ultimately contribute to the development of highly integrated and functional neural networks. Lastly, acute dizocilpine (MK-801) treatment provides new evidence for a direct interaction between collagen-bound GlyCNDs and postsynaptic N-methyl-D-aspartate (NMDA) receptors, thereby suggesting a potential mechanism underlying the observed cellular events. In summary, the findings establish a foundation for the development of a new nanocomposite resulting from the integration of carbon nanomaterials within a clinically approved hydrogel, toward an effective biomaterial-based strategy for addressing neuronal disorders by restoring damaged/lost neurons and supporting the reestablishment of neuroanatomical connectivity.

Breast Cancer Cell Type and Biomechanical Properties of Decellularized Mouse Organs Drives Tumor Cell Colonization

Tissue engineering has emerged as an indispensable tool for the reconstruction of organ-specific environments. Organ-derived extracellular matrices (ECM) and, especially, decellularized tissues (DCL) are recognized as the most successful biomaterials in regenerative medicine, as DCL preserves the most essential organ-specific ECM properties such as composition alongside biomechanics characterized by stiffness and porosity. Expansion of the DCL technology to cancer biology research, drug development, and nanomedicine is pending refinement of the existing DCL protocols whose reproducibility remains sub-optimal varying from organ to organ. We introduce a facile decellularization protocol universally applicable to murine organs, including liver, lungs, spleen, kidneys, and ovaries, with demonstrated robustness, reproducibility, high purification from cell debris, and architecture preservation, as confirmed by the histological and SEM analysis. The biomechanical properties of as-produced DCL organs expressed in terms of the local and total stiffness were measured using our facile methodology and were found well preserved in comparison with the intact organs. To demonstrate the utility of the developed DCL model to cancer research, we engineered three-dimensional tissue constructs by recellularization representative decellularized organs and collagenous hydrogel with human breast cancer cells of pronounced mesenchymal (MDA-MB-231) or epithelial (SKBR-3) phenotypes. The biomechanical properties of the DCL organs were found pivotal to determining the cancer cell fate and progression. Our histological and scanning electron microscopy (SEM) study revealed that the larger the ECM mean pore size and the smaller the total stiffness (as in lung and ovary), the more proliferative and invasive the mesenchymal cells became. At the same time, the low local stiffness ECMs (ranged 2.8-3.6 kPa) did support the epithelial-like SKBR-3 cells' viability (as in lung and spleen), while stiff ECMs did not. The total and local stiffness of the collagenous hydrogel was measured too low to sustain the proliferative potential of both cell lines. The observed cell proliferation patterns were easily interpretable in terms of the ECM biomechanical properties, such as binding sites, embedment facilities, and migration space. As such, our three-dimensional tissue engineering model is scalable and adaptable for pharmacological testing and cancer biology research of metastatic and primary tumors, including early metastatic colonization in native organ-specific ECM.

Negative pressure induces dedifferentiation of hepatocytes via RhoA/ROCK pathway

Biomechanical forces are known to regulate the biological behaviors of cells. Although negative pressure has been used for wound healing, it is still unknown about its role in regulating cell plasticity. We investigated whether negative pressure could induce the dedifferentiation of hepatocytes. Using a commercial device, we found that the exposure of primary human hepatocytes to -50 mmHg quickly induced the formation of stress fibers and obviously changed cell morphology in 72 h. Moreover, the exposure of hepatocytes to -50 mmHg significantly upregulated RhoA, ROCK1, and ROCK2 in 1-6 h, and dramatically enhanced the expression of marker molecules on "stemness", such as OCT4, SOX2, KLF4, MYC, NANOG, and CD133 in 6-72 h. However, all these changes in hepatocytes induced by -50 mmHg stimulation were almost abrogated by ROCK inhibitor Y27623. Our data suggest that an appropriate force of negative pressure stimulation can effectively induce the dedifferentiation of hepatocytes via RhoA/ROCK pathway activation.

Growth and differentiation of human induced pluripotent stem cell (hiPSC)-derived kidney organoids using fully synthetic peptide hydrogels

Human induced pluripotent stem cell (hiPSC)-derived kidney organoids have prospective applications ranging from basic disease modelling to personalised medicine. However, there remains a necessity to refine the biophysical and biochemical parameters that govern kidney organoid formation. Differentiation within fully-controllable and physiologically relevant 3D growth environments will be critical to improving organoid reproducibility and maturation. Here, we matured hiPSC-derived kidney organoids within fully synthetic self-assembling peptide hydrogels (SAPHs) of variable stiffness (storage modulus, G'). The resulting organoids contained complex structures comparable to those differentiated within the animal-derived matrix, Matrigel. Single-cell RNA sequencing (scRNA-seq) was then used to compare organoids matured within SAPHs to those grown within Matrigel or at the air-liquid interface. A total of 13,179 cells were analysed, revealing 14 distinct clusters. Organoid compositional analysis revealed a larger proportion of nephron cell types within Transwell-derived organoids, while SAPH-derived organoids were enriched for stromal-associated cell populations. Notably, differentiation within a higher G' SAPH generated podocytes with more mature gene expression profiles. Additionally, maturation within a 3D microenvironment significantly reduced the derivation of off-target cell types, which are a known limitation of current kidney organoid protocols. This work demonstrates the utility of synthetic peptide-based hydrogels with a defined stiffness, as a minimally complex microenvironment for the selected differentiation of kidney organoids.

Role of extracellular matrix components and structure in new renal models in vitro

The extracellular matrix (ECM), a complex set of fibrillar proteins and proteoglycans, supports the renal parenchyma and provides biomechanical and biochemical cues critical for spatial-temporal patterning of cell development and acquisition of specialized functions. As in vitro models progress towards biomimicry, more attention is paid to reproducing ECM-mediated stimuli. ECM's role in in vitro models of renal function and disease used to investigate kidney injury and regeneration is discussed. Availability, affordability, and lot-to-lot consistency are the main factors determining the selection of materials to recreate ECM in vitro. While simpler components can be synthesized in vitro, others must be isolated from animal or human tissues, either as single isolated components or as complex mixtures, such as Matrigel or decellularized formulations. Synthetic polymeric materials with dynamic and instructive capacities are also being explored for cell mechanical support to overcome the issues with natural products. ECM components can be used as simple 2D coatings or complex 3D scaffolds combining natural and synthetic materials. The goal is to recreate the biochemical signals provided by glycosaminoglycans and other signaling molecules, together with the stiffness, elasticity, segmentation, and dimensionality of the original kidney tissue, to support the specialized functions of glomerular, tubular, and vascular compartments. ECM mimicking also plays a central role in recent developments aiming to reproduce renal tissue in vitro or even in therapeutical strategies to regenerate renal function. Bioprinting of renal tubules, recellularization of kidney ECM scaffolds, and development of kidney organoids are examples. Future solutions will probably combine these technologies.

Contribution of mechanical homeostasis to epithelial-mesenchymal transition

BACKGROUND

Metastasis refers to the spread of cancer cells from a primary tumor to other parts of the body via the lymphatic system and bloodstream. With tremendous effort over the past decades, remarkable progress has been made in understanding the molecular and cellular basis of metastatic processes. Metastasis occurs through five steps, including infiltration and migration, intravasation, survival, extravasation, and colonization. Various molecular and cellular factors involved in the metastatic process have been identified, such as epigenetic factors of the extracellular matrix (ECM), cell-cell interactions, soluble signaling, adhesion molecules, and mechanical stimuli. However, the underlying cause of cancer metastasis has not been elucidated.

CONCLUSION

In this review, we have focused on changes in the mechanical properties of cancer cells and their surrounding environment to understand the causes of cancer metastasis. Cancer cells have unique mechanical properties that distinguish them from healthy cells. ECM stiffness is involved in cancer cell growth, particularly in promoting the epithelial-mesenchymal transition (EMT). During tumorigenesis, the mechanical properties of cancer cells change in the direction opposite to their environment, resulting in a mechanical stress imbalance between the intracellular and extracellular domains. Disruption of mechanical homeostasis may be one of the causes of EMT that triggers the metastasis of cancer cells.

Biological role of matrix stiffness in tumor growth and treatment

In recent years, the biological role of changes in physical factors in carcinogenesis and progression has attracted increasing attention. Matrix stiffness, also known as ECM stress, is a critical physical factor of tumor microenvironment and remains alternating during carcinogenesis as a result of ECM remodeling through activation of cancer-associated fibroblasts and extracellular collagen accumulation, crosslinking and fibrosis. Different content and density of extracellular collagen in ECM endows matrix with varying stiffness. Physical signals induced by matrix stiffness are transmitted to tumor cells primarily by the integrins receptor family and trigger a series of mechanotransduction that result in changes in tumor cell morphology, proliferative capacity, and invasive ability. Importantly, accumulating evidence revealed that changes in matrix stiffness in tumor tissues greatly control the sensitivity of tumor cells in response to chemotherapy, radiotherapy, and immunotherapy through integrin signaling, YAP signaling, and related signaling pathways. Here, the present review analyzes the current research advances on matrix stiffness and tumor cell behavior with a view to contributing to tumor cell growth and treatment, with the hope of improving the understanding of the biological role of matrix stiffness in tumors.

Biomechanical Forces Determine Fibroid Stem Cell Transformation and the Receptivity Status of the Endometrium: A Critical Appraisal

Myometrium cells are an important reproductive niche in which cyclic mechanical forces of a pico-newton range are produced continuously at millisecond and second intervals. Overproduction and/or underproduction of micro-forces, due to point or epigenetic mutation, aberrant methylation, and abnormal response to hypoxia, may lead to the transformation of fibroid stem cells into fibroid-initiating stem cells. Fibroids are tumors with a high modulus of stiffness disturbing the critical homeostasis of the myometrium and they may cause unfavorable and strong mechanical forces. Micro-mechanical forces and soluble-chemical signals play a critical role in transcriptional and translational processes' maintenance, by regulating communication between the cell nucleus and its organelles. Signals coming from the external environment can stimulate cells in the format of both soluble biochemical signals and mechanical ones. The shape of the cell and the plasma membrane have a significant character in sensing electro-chemical signals, through specialized receptors and generating responses, accordingly. In order for mechanical signals to be perceived by the cell, they must be converted into biological stimuli, through a process called mechanotransduction. Transmission of fibroid-derived mechanical signals to the endometrium and their effects on receptivity modulators are mediated through a pathway known as solid-state signaling. It is not sufficiently clear which type of receptors and mechanical signals impair endometrial receptivity. However, it is known that biomechanical signals reaching the endometrium affect epithelial sodium channels, lysophosphatidic acid receptors or Rho GTPases, leading to conformational changes in endometrial proteins. Translational changes in receptivity modulators may disrupt the selectivity and receptivity functions of the endometrium, resulting in failed implantation or early pregnancy loss. By hypermethylation of the receptivity genes, micro-forces can also negatively affect decidualization and implantation. The purpose of this narrative review is to summarize the state of the art of the biomechanical forces which can determine fibroid stem cell transformation and, thus, affect the receptivity status of the endometrium with regard to fertilization and pregnancy.

Hydrogels for Salivary Gland Tissue Engineering

Mimicking the complex architecture of salivary glands (SGs) outside their native niche is challenging due their multicellular and highly branched organization. However, significant progress has been made to recapitulate the gland structure and function using several in vitro and ex vivo models. Hydrogels are polymers with the potential to retain a large volume of water inside their three-dimensional structure, thus simulating extracellular matrix properties that are essential for the cell and tissue integrity. Hydrogel-based culture of SG cells has seen a tremendous success in terms of developing platforms for cell expansion, building an artificial gland, and for use in transplantation to rescue loss of SG function. Both natural and synthetic hydrogels have been used widely in SG tissue engineering applications owing to their properties that support the proliferation, reorganization, and polarization of SG epithelial cells. While recent improvements in hydrogel properties are essential to establish more sophisticated models, the emphasis should still be made towards supporting factors such as mechanotransduction and associated signaling cues. In this concise review, we discuss considerations of an ideal hydrogel-based biomaterial for SG engineering and their associated signaling pathways. We also discuss the current advances made in natural and synthetic hydrogels for SG tissue engineering applications.

Development of a polyacrylamide/chitosan composite hydrogel conduit containing synergistic cues of elasticity and topographies for promoting peripheral nerve regeneration

Substrate elasticity and topographical guidance are crucial factors for regulating tissue regeneration, but the synergistic effects of both cues on peripheral nerve regeneration are still unclear. In this paper, polyacrylamide/chitosan (PAM/CS) composite hydrogels with synergistic characteristics of elasticity and morphology were prepared using in situ free-radical polymerization and micro-molding. The physicochemical properties of hydrogels were characterized, and the effect on peripheral nerve regeneration was systematically evaluated via in vitro and in vivo experiments, respectively. The in vitro experiments showed that on a PAM/CS composite hydrogel with an elastic modulus of 5.822 kPa/8.41 kPa and a surface groove width of 30 μm, the dorsal root ganglion (DRG) neurite had a strong growth ability and better-oriented status. The samples were taken from each group at 2 and 12 weeks after bridging rabbit sciatic nerve defects with a PAM/CS composite hydrogel conduit. General observation of the rabbit body and transplanted nerve, nerve electro-physiological examination, muscle wet weight recovery rate detection and comparison, observation of sciatic nerve frozen section immunofluorescence staining and myelinated nerve fiber recovery rate comparison were used to evaluate the effect of nerve transplantation. The elastic modulus of 8.41 kPa and groove width of 30 μm were similar to those of the autograft group. At the same time, the signaling pathways, including the focal adhesion markers vinculin, p-FAK, and Rho A protein, referring to axon adhesion and extension, were initially revealed. In summary, our developed hydrogel implants containing synergistic cues of elasticity and topographies may provide a new and effective strategy for the treatment of peripheral nerve injury in the future.

The Pathology Lesion Patterns of Podocytopathies: How and why?

Podocytopathies are a group of proteinuric glomerular disorders driven by primary podocyte injury that are associated with a set of lesion patterns observed on kidney biopsy, i.e., minimal changes, focal segmental glomerulosclerosis, diffuse mesangial sclerosis and collapsing glomerulopathy. These unspecific lesion patterns have long been considered as independent disease entities. By contrast, recent evidence from genetics and experimental studies demonstrated that they represent signs of repeated injury and repair attempts. These ongoing processes depend on the type, length, and severity of podocyte injury, as well as on the ability of parietal epithelial cells to drive repair. In this review, we discuss the main pathology patterns of podocytopathies with a focus on the cellular and molecular response of podocytes and parietal epithelial cells.

Electrospinning Fabrication Methods to Incorporate Laminin in Polycaprolactone for Kidney Tissue Engineering

BACKGROUND

Today's treatment options for renal diseases fall behind the need, as the number of patients has increased considerably over the last few decades. Tissue engineering (TE) is one avenue which may provide a new approach for renal disease treatment. This involves creating a niche where seeded cells can function in an intended way. One approach to TE is combining natural extracellular matrix proteins with synthetic polymers, which has been shown to have many positives, yet a little is understood in kidney. Herein, we investigate the incorporation of laminin into polycaprolactone electrospun scaffolds.

METHOD

The scaffolds were enriched with laminin via either direct blending with polymer solution or in a form of emulsion with a surfactant. Renal epithelial cells (RC-124) were cultured on scaffolds up to 21 days.

RESULTS

Mechanical characterization demonstrated that the addition of the protein changed Young's modulus of polymeric fibres. Cell viability and DNA quantification tests revealed the capability of the scaffolds to maintain cell survival up to 3 weeks in culture. Gene expression analysis indicated healthy cells via three key markers.

CONCLUSION

Our results show the importance of hybrid scaffolds for kidney tissue engineering.

Cellular modulation by the mechanical cues from biomaterials for tissue engineering

Mechanical cues from the extracellular matrix (ECM) microenvironment are known to be significant in modulating the fate of stem cells to guide developmental processes and maintain bodily homeostasis. Tissue engineering has provided a promising approach to the repair or regeneration of damaged tissues. Scaffolds are fundamental in cell-based regenerative therapies. Developing artificial ECM that mimics the mechanical properties of native ECM would greatly help to guide cell functions and thus promote tissue regeneration. In this review, we introduce various mechanical cues provided by the ECM including elasticity, viscoelasticity, topography, and external stimuli, and their effects on cell behaviours. Meanwhile, we discuss the underlying principles and strategies to develop natural or synthetic biomaterials with different mechanical properties for cellular modulation, and explore the mechanism by which the mechanical cues from biomaterials regulate cell function toward tissue regeneration. We also discuss the challenges in multimodal mechanical modulation of cell behaviours and the interplay between mechanical cues and other microenvironmental factors.

Mechanotransduction as a major driver of cell behaviour: mechanisms, and relevance to cell organization and future research

How do cells process environmental cues to make decisions? This simple question is still generating much experimental and theoretical work, at the border of physics, chemistry and biology, with strong implications in medicine. The purpose of mechanobiology is to understand how biochemical and physical cues are turned into signals through mechanotransduction. Here, we review recent evidence showing that (i) mechanotransduction plays a major role in triggering signalling cascades following cell-neighbourhood interaction; (ii) the cell capacity to continually generate forces, and biomolecule properties to undergo conformational changes in response to piconewton forces, provide a molecular basis for understanding mechanotransduction; and (iii) mechanotransduction shapes the guidance cues retrieved by living cells and the information flow they generate. This includes the temporal and spatial properties of intracellular signalling cascades. In conclusion, it is suggested that the described concepts may provide guidelines to define experimentally accessible parameters to describe cell structure and dynamics, as a prerequisite to take advantage of recent progress in high-throughput data gathering, computer simulation and artificial intelligence, in order to build a workable, hopefully predictive, account of cell signalling networks.

Advanced mechanotherapy: Biotensegrity for governing metastatic tumor cell fate via modulating the extracellular matrix

Mechano-transduction is the procedure of mechanical stimulus translation via cells, among substrate shear flow, topography, and stiffness into a biochemical answer. TAZ and YAP are transcriptional coactivators which are recognized as relay proteins that promote mechano-transduction within the Hippo pathway. With regard to healthy cells in homeostasis, mechano-transduction regularly restricts proliferation, and TAZ and YAP are totally inactive. During cancer development a YAP/TAZ - stimulating positive response loop is formed between the growing tumor and the stiffening ECM. As tumor developments, local stromal and cancerous cells take advantage of mechanotransduction to enhance proliferation, induce their migratory into remote tissues, and promote chemotherapeutic resistance. As a newly progresses paradigm, nanoparticle-conjunctions (such as magnetic nanoparticles, and graphene derivatives nanoparticles) hold significant promises for remote regulation of cells and their relevant events at molecular scale. Despite outstanding developments in employing nanoparticles for drug targeting studies, the role of nanoparticles on cellular behaviors (proliferation, migration, and differentiation) has still required more evaluations in the field of mechanotherapy. In this paper, the in-depth contribution of mechano-transduction is discussed during tumor progression, and how these consequences can be evaluated in vitro.

Biomaterials for protein delivery for complex tissue healing responses

Tissue repair requires a complex cascade of events mediated by a variety of cells, proteins, and matrix molecules; however, the healing cascade can be easily disrupted by numerous factors, resulting in impaired tissue regeneration. Recent advances in biomaterials for tissue regeneration have increased the ability to tailor the delivery of proteins and other biomolecules to injury sites to restore normal healing cascades and stimulate robust tissue repair. In this review, we discuss the evolution of the field toward creating biomaterials that precisely control protein delivery to stimulate tissue regeneration, with a focus on addressing complex and dynamic injury environments. We highlight biomaterials that leverage different mechanisms to deliver and present proteins involved in healing cascades, tissue targeting and mimicking strategies, materials that can be triggered by environmental cues, and integrated strategies that combine multiple biomaterial properties to improve protein delivery. Improvements in biomaterial design to address complex injury environments will expand our understanding of both normal and aberrant tissue repair processes and ultimately provide a better standard of patient care.

Molecular Mechanisms of Renal Progenitor Regulation: How Many Pieces in the Puzzle?

Kidneys of mice, rats and humans possess progenitors that maintain daily homeostasis and take part in endogenous regenerative processes following injury, owing to their capacity to proliferate and differentiate. In the glomerular and tubular compartments of the nephron, consistent studies demonstrated that well-characterized, distinct populations of progenitor cells, localized in the parietal epithelium of Bowman capsule and scattered in the proximal and distal tubules, could generate segment-specific cells in physiological conditions and following tissue injury. However, defective or abnormal regenerative responses of these progenitors can contribute to pathologic conditions. The molecular characteristics of renal progenitors have been extensively studied, revealing that numerous classical and evolutionarily conserved pathways, such as Notch or Wnt/β-catenin, play a major role in cell regulation. Others, such as retinoic acid, renin-angiotensin-aldosterone system, TLR2 (Toll-like receptor 2) and leptin, are also important in this process. In this review, we summarize the plethora of molecular mechanisms directing renal progenitor responses during homeostasis and following kidney injury. Finally, we will explore how single-cell RNA sequencing could bring the characterization of renal progenitors to the next level, while knowing their molecular signature is gaining relevance in the clinic.

Podocytopathies

Podocytopathies are kidney diseases in which direct or indirect podocyte injury drives proteinuria or nephrotic syndrome. In children and young adults, genetic variants in >50 podocyte-expressed genes, syndromal non-podocyte-specific genes and phenocopies with other underlying genetic abnormalities cause podocytopathies associated with steroid-resistant nephrotic syndrome or severe proteinuria. A variety of genetic variants likely contribute to disease development. Among genes with non-Mendelian inheritance, variants in APOL1 have the largest effect size. In addition to genetic variants, environmental triggers such as immune-related, infection-related, toxic and haemodynamic factors and obesity are also important causes of podocyte injury and frequently combine to cause various degrees of proteinuria in children and adults. Typical manifestations on kidney biopsy are minimal change lesions and focal segmental glomerulosclerosis lesions. Standard treatment for primary podocytopathies manifesting with focal segmental glomerulosclerosis lesions includes glucocorticoids and other immunosuppressive drugs; individuals not responding with a resolution of proteinuria have a poor renal prognosis. Renin-angiotensin system antagonists help to control proteinuria and slow the progression of fibrosis. Symptomatic management may include the use of diuretics, statins, infection prophylaxis and anticoagulation. This Primer discusses a shift in paradigm from patient stratification based on kidney biopsy findings towards personalized management based on clinical, morphological and genetic data as well as pathophysiological understanding.