Operating at multiple levels of control, mesenchymal stem cells from adipose tissue (ADSCs) communicate with organ systems to adjust immune response, provide signals for differentiation, migration, enzymatic reactions, and to equilibrate the regenerative demands of balanced tissue homeostasis. The identification of the mechanisms by which ADSCs accomplish these functions for dermatological rejuvenation and wound healing has great potential to identify novel targets for the treatment of disorders and combat aging. Herein, we review new insights into the role of adipose-derived stem cells in the maintenance of dermal and epidermal homeostasis, and recent advances in clinical applications of ADSCs related to dermatology.

Summary. Background: The platelet fibrinogen receptor, a heterodimer consisting of integrin subunits a IIb and b 3 , is required for platelet aggregation, spreading, and hemostasis. Platelet agonists such as thrombin and adenosine diphosphate (ADP) lead to the activation of a IIb b 3 , thereby enhancing its affinity and avidity for binding fibrinogen (inside-out signaling). Furthermore, fibrinogen binding to a IIb b 3 triggers cytoskeletal changes and granule release (outside-in signaling). Aim: Genetic approaches to characterize the molecular pathways involved in a IIb b 3 signaling are not possible with anucleate blood platelets. Therefore, we have established an OP9 stromal cell co-culture system to generate megakaryocytes from human embryonic stem cells (hESCs). Results: a IIb b 3 activation, measured by soluble fibrinogen binding to hESC-derived megakaryocytes, a þ IIb /GPIba + cells, is readily detectable following stimulation with known platelet agonists. Doseresponse curves for peptide agonists specific for the two platelet thrombin receptors, protease-activated receptor 1 (PAR1) and PAR4, show a relative responsiveness that mirrors that of human platelets, and sub-maximal ADP responses are augmented by epinephrine. Moreover, hESC-derived megakaryocytes undergo lamellipodia formation, actin filament assembly, and vinculin localization at focal adhesions when plated on a fibrinogen-coated surface, characteristic of a IIb b 3 outside-in signaling. Undifferentiated hESCs genetically modified by lentiviral infection can be cloned and maintained in an undifferentiated state and then differentiated into megakaryocytes capable of a IIb b 3 activation. Conclusion: Using hESCs, we have developed a renewable source of human megakaryocytes, and a genetically tractable system for studying megakaryocytopoiesis and a IIb b 3 signaling in the native cellular environment.

Mesenchymal stem/stromal cells (MSC) have been tested in a significant number of clinical trials, where they exhibit regenerative and repair properties directly through their differentiation into the cells of the mesenchymal origin or by modulation of the tissue/organ microenvironment. Despite various clinical effects upon transplantation, the functional properties of these cells in natural settings and their role in tissue regeneration in vivo is not yet fully understood. The omnipresence of MSC throughout vascularized organs equates to a reservoir of potentially therapeutic regenerative depots throughout the body. However, these reservoirs could be subjected to cellular senescence. In this review, we will discuss current progress and challenges in the understanding of different biological pathways leading to senescence. We set out to highlight the seemingly paradoxical property of cellular senescence: its beneficial role in the development and tissue repair and detrimental impact of this process on tissue homeostasis in aging and disease. Taking into account the lessons from the different cell systems, this review elucidates how autocrine and paracrine properties of senescent MSC might impose an additional layer of complexity on the regulation of the immune system in development and disease. New findings that have emerged in the last few years could shed light on sometimes seemingly controversial results obtained from MSC therapeutic applications.

Background aims Heart failure therapy with human embryonic stem cell (hESC)-derived cardiomyocytes (hCM) has been limited by the low rate of spontaneous hCM differentiation. As others have shown that p38 mitogen-activated protein kinase (p38MAPK) directs neurogenesis from mouse embryonic stem cells, we investigated whether the p38MAPK inhibitor, SB203580, might influence hCM differentiation. Methods We treated differentiating hESC with SB203580 at specific time-points, and used flow cytometry, immunocytochemistry, quantitative real-time (RT)–polymerase chain reaction (PCR), teratoma formation and transmission electron microscopy to evaluate cardiomyocyte formation. Results We observed that the addition of inhibitor resulted in 2.1-fold enrichment of spontaneously beating human embryoid bodies (hEB) at 21 days of differentiation, and that 25% of treated cells expressed cardiac-specific α-myosin heavy chain. This effect was dependent on the stage of differentiation at which the inhibitor was introduced. Immunostaining and teratoma formation assays demonstrated that the inhibitor did not affect hESC pluripotency; however, treated hESC gave rise to hCM exhibiting increased expression of sarcomeric proteins, including cardiac troponin T, myosin light chain and α-myosin heavy chain. This was consistent with significantly increased numbers of myofibrillar bundles and the appearance of nascent Z-bodies at earlier time-points in treated hCM. Treated hEB also demonstrated a normal karyotype by array comparative genomic hybridization and viability in vivo following injection into mouse myocardium. Conclusions These studies demonstrate that p38MAPK inhibition accelerates directed hCM differentiation from hESC, and that this effect is developmental stage-specific. The use of this inhibitor should improve our ability to generate hESC-derived hCM for cell-based therapy.

Background aims We have shown previously that inhibition of the p38 mitogen-activated protein kinase (p38MAPK) directs the differentiation of human embryonic stem cell (hESC)-derived cardiomyocytes (hCM). We investigated the therapeutic benefits of intramyocardial injection of hCM differentiated from hESC by p38MAPK inhibition using closed-chest ultrasound-guided injection at a clinically relevant time post-myocardial infarction (MI) in a mouse model. Methods MI was induced in mice and the animals treated at day 3 with: (a) hCM, (b) human fetal fibroblasts (hFF) as cell control, or (c) medium control (n = 10 animals/group). Left ventricular ejection fraction (LVEF) was evaluated post-MI prior to therapy, and at days 28 and 60 post-cell therapy. Hearts were analyzed at day 60 for infarct size, angiogenesis, cell fate and teratoma formation. Results LVEF was improved in the hCM-treated animals compared with both hFF and medium control-treated animals at day 28 (39.03 ± 1.79% versus 27.89 ± 1.27%, P < 0.05, versus 32.90 ± 1.46%, P < 0.05, respectively), with sustained benefit until day 60. hCM therapy resulted in significantly smaller scar size, increased capillary bed area, increased number of arterioles, less native cardiomyocyte (CM) apoptosis, and increased CM proliferation compared with the other two groups. These benefits were achieved despite a very low retention rate of the injected cells at day 60, as assessed by immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR). Therapy with hCM did not result in intramyocardial teratoma formation at day 60. Conclusions This study demonstrates that hCM derived from p38MAPK-treated hESC have encouraging therapeutic potential.