β-Cell replacement as a treatment for type 1 diabetes: an overview of possible cell sources and current axes of research

To efficiently treat type 1 diabetes, exogenous insulin injections currently represent the main approach to counter chronic hyperglycaemia. Unfortunately, such a therapeutic approach does not allow for perfectly maintained glucose homeostasis and, in time, cardiovascular complications may arise. Therefore, seeking alternative/improved treatments has become a major health concern as an increasing proportion of type 2 diabetes patients also require insulin supplementation. Towards this goal, numerous laboratories have focused their research on β-cell replacement therapies. Herein, we will review the current state of this research area and describe the cell sources that could potentially be used to replenish the depleted β-cell mass in diabetic patients.

In vivo conversion of adult α-cells into β-like cells: a new research avenue in the context of type 1 diabetes

Type 1 diabetes is caused by the loss of insulin-producing β-cells as a result of an autoimmune condition. Despite current therapeutic approaches aimed at restoring the insulin supply, complications caused by variations in glycaemia may still arise with age. There is therefore mounting interest in the establishment of alternative therapies. Most current approaches consist in designing rational protocols for in vitro or in vivo cell differentiation/reprogramming from a number of cell sources, including stem, progenitor or differentiated cells. Towards this ultimate goal, it is clear that we need to gain further insight into the interplay between signalling events and transcriptional networks that act in concert throughout pancreatic morphogenesis. This short review will therefore focus on the main events underlying pancreatic development with particular emphasis on the genetic determinants implicated, as well as on the relatively new concept of endocrine cell reprogramming, that is the conversion of pancreatic α-cells into cells displaying a β-cell phenotype.

The homeobox gene Arx is a novel positive regulator of embryonic myogenesis

Skeletal muscle fibers form in overlapping, but distinct phases that depend on the generation of temporally different lineages of myogenic cells. During primary myogenesis (E10.5-E12.5 in the mouse), embryonic myoblasts fuse homotypically to generate primary fibers, whereas during later development (E14.5-E17.5), fetal myoblasts differentiate into secondary fibers. How these myogenic waves are regulated remains largely unknown. Studies have been hampered by the lack of markers which would distinguish embryonic from fetal myoblast populations. We show here that the homeobox gene Arx is strongly expressed in differentiating embryonic muscle, downstream of myogenic basic helix-loop-helix (bHLH) genes. Its expression progressively decreases during development. When overexpressed in the C2C12 myogenic cell line, Arx enhances differentiation. Accordingly, it stimulates the transcriptional activity from the Myogenin promoter and from multimerized E-boxes when co-expressed with MyoD and Mef2C in CH310T1/2. Furthermore, Arx co-immunoprecipitates with Mef2C, suggesting that it participates in the transcriptional regulatory network acting in embryonic muscle. Finally, embryonic myoblasts isolated from Arx-deficient embryos show a delayed differentiation in vivo together with an enhanced clonogenic capacity in vitro. We propose here that Arx acts as a novel positive regulator of embryonic myogenesis by synergizing with Mef2C and MyoD and by establishing an activating loop with Myogenin.

Double-intensive therapy in high-risk multiple myeloma

A high remission rate is achieved with high-dose melphalan (HDM) in multiple myeloma (MM), and autologous transplantation of hematopoietic stem cells allows a prompt hematologic recovery after high-dose therapy. We treated 97 patients with high-risk MM (group 1:44 advanced MM including 14 primary resistances and 30 relapses; group 2: 53 newly diagnosed MM) with a first course of HDM. For responding patients a second course of high-dose therapy with hematopoietic stem cell support was proposed. After the first HDM, the overall response and complete remission rates were 71% and 25% with no significant difference between the two groups. The median durations of neutropenia and thrombocytopenia were significantly longer in group 1 (29.5 days and 32 days, respectively) than in group 2 (23 days and 17 days, respectively). This severe myelosuppression led to eight toxic deaths and the fact that only 38 of the 69 responders could proceed to the second course (three allogenic and 35 autologous transplantations). Among the 35 patients undergoing autologous transplantation (10 in group 1, 25 in group 2), 31 received their marrow unpurged collected after the first HDM, and four received peripheral blood stem cells. The median durations of neutropenia and thrombocytopenia after autologous transplantation were 24 days and 49 days, respectively. Two toxic deaths and nine prolonged thrombocytopenias were observed. The median survival for the 97 patients was 24 months (17 months in group 1, 37 months in group 2) and the median duration of response was 20 months. The only parameters that have a significant impact on the survival are the age (+/- 50 years) and the response to HDM. The median survival of the 35 patients undergoing autologous transplantation is 41 months, but the median duration of remission is 28 months with no plateau of the remission duration curve. Patients responding to HDM may have prolonged survival, but even a second course of high-dose therapy probably cannot eradicate the malignant clone.