Human Adipocyte Conditioned Medium Promotes In Vitro Fibroblast Conversion to Myofibroblasts

Development and analysis of scaffold-free adipose spheroids

Adipose tissue plays a crucial role in metabolic syndrome, autoimmune diseases, and many cancers. Because of adipose's role in so many aspects of human health, there is a critical need for in vitro models that replicate adipose architecture and function. Traditional monolayer models, despite their convenience, are limited, showing heterogeneity and functional differences compared to 3D models. While monolayer cultures struggle with detachment and inefficient differentiation, healthy adipocytes in 3D culture accumulate large lipid droplets, secrete adiponectin, and produce low levels of inflammatory cytokines. The shift from monolayer models to more complex 3D models aims to better replicate the physiology of healthy adipose tissue in culture. This study introduces a simple and accessible protocol for generating adipose organoids using a scaffold-free spheroid model. The method, utilizing either 96-well spheroid plates or agarose micromolds, demonstrates increased throughput, uniformity, and ease of handling compared to previous techniques. This protocol allows for diverse applications, including drug testing, toxin screening, tissue engineering, and co-culturing. The choice between the two methods depends on the experimental goals, with the 96-well plate providing individualized control and the micromold offering scale advantages. The outlined protocol covers isolation, expansion, and characterization of stromal vascular fraction cells, followed by detailed steps for spheroid formation and optional downstream analyses.

Fibroblast-Adipocyte Lineage Cell Interactions Result in Differential Production of Extracellular Matrix Proteins

Introduction

Scarring from traumatic injury, burns, and other complications remains a significant problem that diminishes quality of life for millions of people worldwide. A common target for the development of new therapies to promote healing and reduce scarring are myofibroblasts because of their central role in pathological scarring. Recent work indicates that adipocyte lineage cells also contribute to the wound healing process, including clinical reports that indicate that the placement of autologous adipose micrografts at the surgical site improves the appearance and pliability of existing scars.

Methods

To better understand how adipocyte lineage cells interact with fibroblasts to promote healing, we first utilized an in vitro model of wound healing to visualize fibroblast spheroid collagen deposition via time-lapse imaging. We then introduced pre-adipocyte and adipocyte spheroids to visualize pair-wise spheroid interactions and collagen deposition among all three cell types. Finally, we quantified differences in the extracellular matrix (ECM) proteins produced using liquid chromatography with tandem mass spectrometry (LC-MS/MS).

Results

We found that all three cell-types contribute to ECM deposition and that the composition of the ECM proteins, or matrisome, was significantly different depending on which cells were co-cultured together.

Conclusions

By better understanding the interactions among these cell types, novel adipose-tissue-based therapeutic approaches can be developed to improve wound healing and reduce scar tissue.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00829-8.

Mature adipocytes inhibit differentiation of myogenic cells but stimulate proliferation of fibro-adipogenic precursors derived from trout muscle in vitro

Interactions between tissues and cell types, mediated by cytokines or direct cell-cell exchanges, regulate growth. To determine whether mature adipocytes influence the in vitro growth of trout mononucleated muscle cells, we developed an indirect coculture system, and showed that adipocytes (5 × 106 cells/well) derived from perivisceral adipose tissue increased the proliferation (BrdU-positive cells) of the mononucleated muscle cells (26% vs. 39%; p < 0.001) while inhibiting myogenic differentiation (myosin+) (25% vs. 15%; p < 0.001). Similar effects were obtained with subcutaneous adipose tissue-derived adipocytes, although requiring more adipocytes (3 × 107 cells/well vs. 5 × 106 cells/well). Conditioned media recapitulated these effects, stimulating proliferation (31% vs. 39%; p < 0.001) and inhibiting myogenic differentiation (32 vs. 23%; p < 0.001). Adipocytes began to reduce differentiation after 24 h, whereas proliferation stimulation was observed after 48 h. While adipocytes did not change pax7+ and myoD1/2+ percentages, they reduced myogenin+ cells showing inhibition from early differentiation stage. Finally, adipocytes increased BrdU+ cells in the Pdgfrα+ population but not in the myoD+ one. Collectively, our results demonstrate that trout adipocytes promote fibro-adipocyte precursor proliferation while inhibiting myogenic cells differentiation in vitro, suggesting the key role of adipose tissue in regulating fish muscle growth.

Native adiponectin plays a role in the adipocyte-mediated conversion of fibroblasts to myofibroblasts

Adipocytes regulate tissues through production of adipokines that can act both locally and systemically. Adipocytes also have been found to play a critical role in regulating the healing process. To better understand this role, we developed a three-dimensional human adipocyte spheroid system that has an adipokine profile similar to in vivo adipose tissues. Previously, we found that conditioned medium from these spheroids induces human dermal fibroblast conversion into highly contractile, collagen-producing myofibroblasts through a transforming growth factor beta-1 (TGF-β1) independent pathway. Here, we sought to identify how mature adipocytes signal to dermal fibroblasts through adipokines to induce myofibroblast conversion. By using molecular weight fractionation, heat inactivation and lipid depletion, we determined mature adipocytes secrete a factor that is 30-100 kDa, heat labile and lipid associated that induces myofibroblast conversion. We also show that the depletion of the adipokine adiponectin, which fits those physico-chemical parameters, eliminates the ability of adipocyte-conditioned media to induce fibroblast to myofibroblast conversion. Interestingly, native adiponectin secreted by cultured adipocytes consistently elicited a stronger level of α-smooth muscle actin expression than exogenously added adiponectin. Thus, adiponectin secreted by mature adipocytes induces fibroblast to myofibroblast conversion and may lead to a phenotype of myofibroblasts distinct from TGF-β1-induced myofibroblasts.

Mechanisms underlying pathological scarring by fibroblasts during wound healing

Pathological scarring is an abnormal outcome of wound healing, which often manifests as excessive proliferation and transdifferentiation of fibroblasts (FBs), and excessive deposition of the extracellular matrix. FBs are the most important effector cells involved in wound healing and scar formation. The factors that promote pathological scar formation often act on the proliferation and function of FB. In this study, we describe the factors that lead to abnormal FB formation in pathological scarring in terms of the microenvironment, signalling pathways, epigenetics, and autophagy. These findings suggest that understanding the causes of abnormal FB formation may aid in the development of precise and effective preventive and treatment strategies for pathological scarring that are associated with improved quality of life of patients.

Novel prospects for scarless wound healing: The roles of myofibroblasts and adipocytes

Disturbances or defects in the process of wound repair can disrupt the delicate balance of cells and molecules necessary for complete wound healing, thus leading to chronic wounds or fibrotic scars. Myofibroblasts are one of the most important cells involved in fibrotic scars, and reprogramming provides a potential avenue to increase myofibroblast clearance. Although myofibroblasts have long been recognized as terminally differentiated cells, recent studies have shown that myofibroblasts have the capacity to be reprogrammed into adipocytes. This review intends to summarize the potential of reprogramming myofibroblasts into adipocytes. We will discuss myofibroblast lineage tracing, as well as the known mechanisms underlying adipocyte regeneration from myofibroblasts. In addition, we investigated different changes in myofibroblast gene expression, transcriptional regulators, signalling pathways and epigenetic regulators during skin wound healing. In the future, myofibroblast reprogramming in wound healing will be better understood and appreciated, which may provide new ideas for the treatment of scarless wound healing.

Force-Bioreactor for Assessing Pharmacological Therapies for Mechanobiological Targets

Tissue fibrosis is a major health issue that impacts millions of people and is costly to treat. However, few effective anti-fibrotic treatments are available. Due to their central role in fibrotic tissue deposition, fibroblasts and myofibroblasts are the target of many therapeutic strategies centered primarily on either inducing apoptosis or blocking mechanical or biochemical stimulation that leads to excessive collagen production. Part of the development of these drugs for clinical use involves in vitro prescreening. 2D screens, however, are not ideal for discovering mechanobiologically significant compounds that impact functions like force generation and other cell activities related to tissue remodeling that are highly dependent on the conditions of the microenvironment. Thus, higher fidelity models are needed to better simulate in vivo conditions and relate drug activity to quantifiable functional outcomes. To provide guidance on effective drug dosing strategies for mechanoresponsive drugs, we describe a custom force-bioreactor that uses a fibroblast-seeded fibrin gels as a relatively simple mimic of the provisional matrix of a healing wound. As cells generate traction forces, the volume of the gel reduces, and a calibrated and embedded Nitinol wire deflects in proportion to the generated forces over the course of 6 days while overhead images of the gel are acquired hourly. This system is a useful in vitro tool for quantifying myofibroblast dose-dependent responses to candidate biomolecules, such as blebbistatin. Administration of 50 μM blebbistatin reliably reduced fibroblast force generation approximately 40% and lasted at least 40 h, which in turn resulted in qualitatively less collagen production as determined via fluorescent labeling of collagen.

Bio-engineering a prevascularized human tri-layered skin substitute containing a hypodermis

Severe injuries to skin including hypodermis require full-thickness skin replacement. Here, we bioengineered a tri-layered human skin substitute (TLSS) containing the epidermis, dermis, and hypodermis. The hypodermal layer was generated by differentiation of human adipose stem cells (ASC) in a collagen type I hydrogel and combined with a prevascularized dermis consisting of human dermal microvascular endothelial cells and fibroblasts, which arranged into a dense vascular network. Subsequently, keratinocytes were seeded on top to generate the epidermal layer of the TLSS. The differentiation of ASC into adipocytes was confirmed in vitro on the mRNA level by the presence of adiponectin, as well as by the expression of perilipin and FABP-4 proteins. Moreover, functional characteristics of the hypodermis in vitro and in vivo were evaluated by Oil Red O, BODIPY, and AdipoRed stainings visualizing intracellular lipid droplets. Further, we demonstrated that both undifferentiated ASC and mature adipocytes present in the hypodermis influenced the keratinocyte maturation and homeostasis in the skin substitutes after transplantation. In particular, an enhanced secretion of TGF-β1 by these cells affected the epidermal morphogenesis as assessed by the expression of key proteins involved in the epidermal differentiation including cytokeratin 1, 10, 19 and cornified envelope formation such as involucrin. Here, we propose a novel functional hypodermal-dermo-epidermal tri-layered skin substitute containing blood capillaries that efficiently promote regeneration of skin defects. STATEMENT OF SIGNIFICANCE: The main objective of this study was to develop and assess the usefulness of a tri-layered human prevascularized skin substitute (TLSS) containing an epidermis, dermis, and hypodermis. The bioengineered hypodermis was generated from human adipose mesenchymal stem cells (ASC) and combined with a prevascularized dermis and epidermis. The TLSS represents an exceptional model for studying the role of cell-cell and cell-matrix interactions in vitro and in vivo. In particular, we observed that enhanced secretion of TGF-β1 in the hypodermis exerted a profound impact on fibroblast and keratinocyte differentiation, as well as epidermal barrier formation and homeostasis. Therefore, improved understanding of the cell-cell interactions in such a physiological skin model is essential to gain insights into different aspects of wound healing.

Mechanical interactions of invasive cancer cells through their substrate evolve from additive to synergistic

Non-contacting, adjacent cancer cells can mechanically interact through their substrate to increase their invasive and migratory capacities that underly metastases-formation. Such mechanical interactions may induce additive or synergistic enhancement of invasiveness, potentially indicating different underlying force-mechanisms. To identify cell-cell-gel interactions, we monitor the time-evolution of three-dimensional traction strains induced by MDA-MB-231 breast cancer cells adhering on physiological-stiffness (1.8 kPa) collagen gels and compare to simulations. Single metastatic cells apply strain energies of 0.2-2 pJ (average 0.51 ± 0.06 pJ) at all observation times (30-174 min) inducing a mechanical volume-of-effect in the collagen gel that is initially (<60 min from seeding) on the cell-volume scale (∼3000 µm³) and on average increases with time from cell seeding. When cells adhere closely adjacent, at short times (<60 min) we distinguish the additive contributions of neighboring cells to the strains, while at longer times strain fields are synergistically amplified and may facilitate increased cooperative/collective cancer-cell-invasiveness. The results of well-spaced and closely adjacent cells at short times match our simulations of additive deformations induced by radially applied strains with experimentally based inverse-distance decay. We thus reveal a time-dependent evolution from additive to synergistic interactions of adjacently adhering cells that may facilitate metastatic invasion.

The Prognosis of Arthrofibroses: Prevalence, Clinical Shortcomings, and Future Prospects

Fibrosis is the dysregulated biosynthesis of connective tissue that results from persistent infection, high serum cholesterol, surgery, trauma, or prolonged joint immobilization. As a disease that impacts connective tissue, it is prevalent across the body and disrupts normal extracellular and tissue organization. Ultimately, fibrosis impairs the tissue structural, mechanical, or biochemical function. This review describes the clinical landscape of joint fibrosis, that is, arthrofibrosis, including the risk factors and causes, as well as current clinical treatments and their shortcomings. Because treating arthrofibrosis remains an unmet clinical challenge, we present several animal models used for exploration of the physiopathology of arthrofibrosis and summarize their use for testing novel treatments. We then discuss therapeutics for the prevention or treatment of arthrofibrosis that are in preclinical development and in ongoing clinical trials. We conclude with recent findings from molecular biological studies of arthrofibroses that shed insight on future areas of research for improved treatments.

Dermal Drivers of Injury-Induced Inflammation: Contribution of Adipocytes and Fibroblasts

Irregular inflammatory responses are a major contributor to tissue dysfunction and inefficient repair. Skin has proven to be a powerful model to study mechanisms that regulate inflammation. In particular, skin wound healing is dependent on a rapid, robust immune response and subsequent dampening of inflammatory signaling. While injury-induced inflammation has historically been attributed to keratinocytes and immune cells, a vast body of evidence supports the ability of non-immune cells to coordinate inflammation in numerous tissues and diseases. In this review, we concentrate on the active participation of tissue-resident adipocytes and fibroblasts in pro-inflammatory signaling after injury, and how altered cellular communication from these cells can contribute to irregular inflammation associated with aberrant wound healing. Furthering our understanding of how tissue-resident mesenchymal cells contribute to inflammation will likely reveal new targets that can be manipulated to regulate inflammation and repair.

Adipose Tissue: A Source of Stem Cells with Potential for Regenerative Therapies for Wound Healing

Interest in adipose tissue is fast becoming a focus of research after many years of being considered as a simple connective tissue. It is becoming increasingly apparent that adipose tissue contains a number of diverse cell types, including adipose-derived stem cells (ASCs) with the potential to differentiate into a number of cell lineages, and thus has significant potential for developing therapies for regenerative medicine. Currently, there is no gold standard treatment for scars and impaired wound healing continues to be a challenge faced by clinicians worldwide. This review describes the current understanding of the origin, different types, anatomical location, and genetics of adipose tissue before discussing the properties of ASCs and their promising applications for tissue engineering, scarring, and wound healing.