Adenovirus-mediated expression of hypoxia-inducible factor 1α double mutant converts neonatal cardiac fibroblasts into (cardio)myocyte phenotype

Reprogramming and transdifferentiation - two key processes for regenerative medicine

Regenerative medicine based on transplants obtained from donors or foetal and new-born mesenchymal stem cells, encounter important obstacles such as limited availability of organs, ethical issues and immune rejection. The growing demand for therapeutic methods for patients being treated after serious accidents, severe organ dysfunction and an increasing number of cancer surgeries, exceeds the possibilities of the therapies that are currently available. Reprogramming and transdifferentiation provide powerful bioengineering tools. Both procedures are based on the somatic differentiated cells, which are easily and unlimitedly available, like for example: fibroblasts. During the reprogramming procedure mature cells are converted into pluripotent cells - which are capable to differentiate into almost any kind of desired cells. Transdifferentiation directly converts differentiated cells of one type into another differentiated cells type. Both procedures allow to obtained patient's dedicated cells for therapeutic purpose in regenerative medicine. In combination with biomaterials, it is possible to obtain even whole anatomical structures. Those patient's dedicated structures may serve for them upon serious accidents with massive tissue damage but also upon cancer surgeries as a replacement of damaged organ. Detailed information about reprogramming and transdifferentiation procedures as well as the current state of the art are presented in our review.

Hypoxia preconditioning promotes cardiac stem cell survival and cardiogenic differentiation in vitro involving activation of the HIF-1α/apelin/APJ axis

BACKGROUND

Cardiac stem cells (CSCs) transplantation has been regarded as an optimal therapeutic approach for cardiovascular disease. However, inferior survival and low differentiation efficiency of these cells in the local infarct site reduce their therapeutic efficacy. In this study, we investigated the influence of hypoxia preconditioning (HP) on CSCs survival and cardiogenic differentiation in vitro and explored the relevant mechanism.

METHODS

CSCs were obtained from Sprague-Dawley rats and cells of the third passage were cultured in vitro and exposed to hypoxia (1% O₂). Cells survival and apoptosis were evaluated by MTS assay and flow cytometry respectively. Cardiogenic differentiation was induced by using 5-azacytidine for another 24 h after the cells experienced HP. Normoxia (20% O₂) was used as a negative control during the whole process. Cardiogenic differentiation was assessed 2 weeks after the induction. Relevant molecules were examined after HP and during the differentiation process. Anti-hypoxia-inducible factor-1α (HIF-1α) small interfering RNA (siRNA), anti-apelin siRNA, and anti-putative receptor protein related to the angiotensin receptor AT1 (APJ) siRNA were transfected in order to block their expression, and relevant downstream molecules were detected.

RESULTS

Compared with the normoxia group, the hypoxia group presented more rapid growth at time points of 12 and 24 h (p < 0.01). Cells exhibited the highest proliferation rate at the time point of 24 h (p < 0.01). The cell apoptosis rate significantly declined after 24 h of hypoxia exposure (p < 0.01). Expression levels of HIF-1α, apelin, and APJ were all enhanced after HP. The percentage of apelin, α-SA, and cTnT positive cells was greatly increased in the HP group after 2 weeks of induction. The protein level of α-SA and cTnT was also significantly elevated at 7 and 14 days (p < 0.01). HIF-1α, apelin, and APJ were all increased at different time points during the cardiogenic differentiation process (p < 0.01). Knockdown of HIF-1α, apelin or APJ by siRNAs resulted in a significant reduction of α-SA and cTnT. HIF-1α blockage caused a remarkable decrease of apelin and APJ (p < 0.01). Expression levels of apelin and APJ were depressed after the inhibition of apelin (p < 0.01).

CONCLUSION

HP could effectively promote CSCs survival and cardiogenic differentiation in vitro, and this procedure involved activation of the HIF-1α/apelin/APJ axis. This study provided a new perspective for exploring novel strategies to enhance CSCs transplantation efficiency.

Pro-myogenic and low-oxygen culture increases expression of contractile smooth muscle markers in human fibroblasts

Smooth muscle cells (SMCs) are essential for tissue engineering strategies to fabricate organs such as blood vessels, the oesophagus and bladder, and to create disease models of these systems. In order for such therapies and models to be feasible, SMCs must be sourced effectively to enable production of large numbers of functional cells. In vitro, SMCs divide slowly and demonstrate short proliferative lifespans compared with other types of cells, including stem cells and fibroblasts, limiting the number of cells that can be derived from expansion in culture of a primary isolation. As such, it would be beneficial to better understand the factors underlying induction and maintenance of SMC phenotypes, in order to produce new sources of SMCs for tissue engineering and disease modelling. Here we report the ability of human dermal fibroblasts to display patterns of gene expression resembling contractile SMCs when cultured under conditions that are known to promote a contractile phenotype in SMCs, including culture on collagen IV, low-serum culture, TGF-β1 treatment and hypoxia. These factors drive expression of the myogenic transcription factor myocardin, as well as expression of several of its gene targets that are known contributors to contractile phenotype in SMCs, including smooth muscle alpha actin, calponin, and myosin heavy chain. Our results suggest that culture conditions associated with culture of SMCs may be sufficient to induce myogenic gene expression patterns and potential myogenic function in non-muscle cells.

In search of novel targets for heart disease: myocardin and myocardin-related transcriptional cofactors

Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.