Towards standardization of human adipose-derived stromal cells secretomes.

The secretome of adipose-derived stromal cells (ASC) is a heterogeneous mixture of components with a beneficial influence on cellular microenvironments. As such, it represents a cell-free alternative in regenerative medicine therapies. Pathophysiological conditions increase the therapeutic capacity of ASC and, with this, the benefits of the secretome. Such conditions can be partially mimicked in vitro by adjusting culturing conditions. Secretomics, the unbiased analysis of a cell secretome by mass spectrometry, is a powerful tool to describe the composition of ASC secretomes. In this proteomics databases review, we compared ASC secretomic studies to retrieve persistently reported proteins resulting from the most explored types of culturing conditions used in research, i.e., exposure to normoxia, hypoxia, or cytokines. Our comparisons identified only eight common proteins within ASC normoxic secretomes, no commonalities within hypoxic ASC secretomes, and only nine within secretomes of ASC exposed to proinflammatory cytokines. Within these, and regardless of the culturing condition that stimulated secretion, a consistent presence of extracellular matrix-related pathways associated with such proteins was identified. Confounders such as donors' age, sex, body mass index, the anatomical area where ASC were harvested, secretome collection method, data description, and how the data is shared with the scientific community are discussed as factors that might explain our outcomes. We conclude that standardization is imperative as the currently available ASC secretomic studies do not facilitate solid conclusions on the therapeutic value of different ASC secretomes.

From Macro to Micro: Comparison of Imaging Techniques to Detect Vascular Network Formation in Left Ventricle Decellularized Extracellular Matrix Hydrogels.

Background: Angiogenesis is a crucial process in physiological maintenance and tissue regeneration. To understand the contribution of angiogenesis, it is essential to replicate this process in an environment that reproduces the biochemical and physical properties which are largely governed by the extracellular matrix (ECM). We investigated vascularization in cardiac left ventricular ECM hydrogels to mimic post-myocardial repair. We set out to assess and compare different destructive and non-destructive methods, optical as well as non-optical, to visualize angiogenesis and associated matrix remodeling in myocardial ECM hydrogels. Methods: A total of 100,000, 300,000, and 600,000 Human Pulmonary Microvascular Endothelial Cells (HPMEC) were seeded in left ventricular cardiac ECM hydrogel in 48-well plates. After 1, 7, and 14 days of culture, the HPMEC were imaged by inverted fluorescence microscopy and 3D confocal laser scanning microscopy (Zeiss Cell Discoverer 7). In addition, cell-seeded ECM hydrogels were scanned by optical coherence tomography (OCT). Fixed and paraffin-embedded gels were thin-sectioned and assessed for ECM components via H&E, picrosirius red histochemical staining, and immunostaining for collagen type I. ImageJ-based densitometry was used to quantify vascular-like networks and GraphPad was used for statistical analyses. Results: Qualitative analyses were realized through fluoromicrographs obtained by the confocal laser scanning microscope which allowed us to visualize the extensive vascular-like networks that readily appeared at all seeding densities. Quantification of networks was only possible using fluoromicrographs from inverted microscopy. These showed that, after three days, the number of master junctions was seeding density-dependent. The resolution of optical coherence tomography was too low to distinguish between signals caused by the ECM and cells or networks, yet it did show that gels, irrespective of cells, were heterogeneous. Interestingly, (immuno)histochemistry could clearly distinguish between the cast cardiac-derived matrix and newly deposited ECM in the hydrogels. The H&E staining corroborated the presence of vascular-like network structures, albeit that sectioning inevitably led to the loss of 3D structure. Conclusions: Except for OCT, all methods had complementary merit and generated qualitative and quantitative data that allowed us to understand vascular network formation in organ-derived ECM hydrogels.

Adipose tissue-derived ECM hydrogels and their use as 3D culture scaffold.

Adipose tissue has the therapeutic capacity in the form of a fat graft, for example, for treatment of irradiation-induced scars and difficult to heal dermal wounds. For large-scale clinical application, an off-the-shelf product is warranted. In recent years, ECM-derived hydrogels are postulated to harbour therapeutic capacity and might even replicate the beneficial effects of adipose tissue. In normal homeostasis, the natural ECM acts as a deposit of growth factors, that releases them over time. In the healing of lesions, this might promote cell accumulation and proliferation which in turn stimulates angiogenesis and repair. The decellularization of tissue and the generation of hydrogels may leave cytotoxic traces. Therefore, our research assessed the cytotoxic effect of human adipose tissue-derived ECM hydrogels on connective tissue cells i.e. fibroblasts. The results showed no cytotoxicity, meaning the hydrogels caused no cell death. Cell migration and survival were observed when cultured in ECM hydrogels and followed for 7 days. Cell survival in the hydrogel was confirmed with CFDA staining and also cells showed the ability to penetrate and migrate throughout the gel. We conclude that ECM hydrogels are promising to use as innovative therapy for wound healing.

Adipose tissue-derived extracellular matrix hydrogels as a release platform for secreted paracrine factors.

Fat grafting is an established clinical intervention to promote tissue repair. The role of the fat's extracellular matrix (ECM) in regeneration is largely neglected. We investigated in vitro the use of human adipose tissue-derived ECM hydrogels as release platform for factors secreted by adipose-derived stromal cells (ASCs). Lipoaspirates from nondiabetic and diabetic donors were decellularized. Finely powdered acellular ECM was evaluated for cell remainders and DNA content. Acellular ECM was digested, and hydrogels were formed at 37°C and their viscoelastic relaxation properties investigated. Release of ASC-released factors from hydrogels was immune assessed, and bio-activity was determined by fibroblast proliferation and migration and endothelial angiogenesis. Acellular ECM contained no detectable cell remainders and negligible DNA contents. Viscoelastic relaxation measurements yielded no data for diabetic-derived hydrogels due to gel instability. Hydrogels released several ASC-released factors concurrently in a sustained fashion. Functionally, released factors stimulated fibroblast proliferation and migration as well as angiogenesis. No difference between nondiabetic and diabetic hydrogels in release of factors was measured. Adipose ECM hydrogels incubated with released factors by ASC are a promising new therapeutic modality to promote several important wound healing-related processes by releasing factors in a controlled way.