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A growing body of scientific reports indicates that the role of creatine (Cr) in cellular biochemistry and physiology goes beyond its contribution to cell energy. Indeed Cr has been shown to exert multiple effects promoting a wide range of physiological responses in vitro as well as in vivo. Included in these, Cr promotes in vitro neuron and muscle cell differentiation, viability and survival under normal or adverse conditions; anabolic, protective and pro-differentiative effects have also been observed in vivo. For example Cr has been shown to accelerate in vitro differentiation of cultured C2C12 myoblasts into myotubes, where it also induces a slight but significant hypertrophic effect as compared to unsupplemented cultures; Cr also prevents the anti-differentiation effects caused by oxidative stress in the same cells. In trained adults, Cr increases the mRNA expression of relevant myogemic factors, protein synthesis, muscle strength and size, in cooperation with physical exercise. As to neurons and central nervous system, Cr favors the electrophysiological maturation of chick neuroblasts in vitro and protects them from oxidative stress-caused killing; similarly, Cr promotes the survival and differentiation of GABA-ergic neurons in fetal spinal cord cultures in vitro; in vivo, maternal Cr supplementation promotes the morpho-functional development of hippocampal neurons in rat offsprings. This article, which presents also some new experimental data, focuses on the trophic, pro-survival and pro-differentiation effects of Cr and examines the ensuing preventive and therapeutic potential in pathological muscle and brain conditions.

Creatine (Cr) is a nutritional supplement promoting a number of health benefits. Indeed Cr has been shown to be beneficial in disease-induced muscle atrophy, improve rehabilitation, and afford mild antioxidant activity. The beneficial effects are likely to derive from pleiotropic interactions. In accord with this notion, we previously demonstrated that multiple pleiotropic effects, including preservation of mitochondrial damage, account for the capacity of Cr to prevent the differentiation arrest caused by oxidative stress in C2C12 myoblasts. Given the importance of mitochondria in supporting the myogenic process, here we further explored the protective effects of Cr on the structure, function, and networking of these organelles in C2C12 cells differentiating under oxidative stressing conditions; the effects on the energy sensor AMPK, on PGC-1α, which is involved in mitochondrial biogenesis and its downstream effector Tfam were also investigated. Our results indicate that damage to mitochondria is crucial in the differentiation imbalance caused by oxidative stress and that the Cr-prevention of these injuries is invariably associated with the recovery of the normal myogenic capacity. We also found that Cr activates AMPK and induces an upregulation of PGC-1α expression, two events which are likely to contribute to the protection of mitochondrial quality and function.

Among the numerous functions of melatonin, the control of survival and differentiation of mesenchymal stem cells (MSCs) has been recently proposed. MSCs are a heterogeneous population of multipotent elements resident in tissues such as bone marrow, muscle, and adipose tissue, which are primarily involved in developmental and regeneration processes, gaining thus increasing interest for tissue repair and restoration therapeutic protocols. Receptor-dependent and receptor-independent responses to melatonin are suggested to occur in these cells. These involve antioxidant or redox-dependent functions of this indolamine as well as secondary effects resulting from autocrine and paracrine responses. Inflammatory cytokines and adipokines, proangiogenic/mitogenic stimuli, and other mediators that influence the differentiation processes may affect the survival and functional integrity of these mesenchymal precursor cells. In this scenario, melatonin seems to regulate signaling pathways that drive commitment and differentiation of MSC into osteogenic, chondrogenic, adipogenic, or myogenic lineages. Common pathways suggested to be involved as master regulators of these processes are the Wnt/β-catenin pathway, the MAPKs and the, TGF-β signaling. In this respect melatonin emerges a novel and potential modulator of MSC lineage commitment and adipogenic differentiation. These and other aspects of the physiological and pharmacological effects of melatonin as regulator of MSC are discussed in this review., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Cytotoxic functions and susceptibility to apoptosis are crucial aspects of NK cells suitable to counter cancer after infusion in oncologic patients. To test the feasibility and the usefulness of infusing in vitro generated NK cells, these two features were investigated in NK cells developed in vitro from CD34⁺ hematopoietic progenitors. Purified CD34⁺ cells were cultured for 15-30 days with FLT-3 ligand (FLT3-L) and IL-15 with or without IL-21. To induce terminal differentiation, NK cells were cultured for further 15 days with IL-15, IL-21, or their combination. A CD56(dim) /CD16⁺ NK subset, expressing high level of perforin, granzymes, and LFA-1, appeared early in cultures with FLT3-L, IL-15, and IL-21, but it quickly died, indicating its predisposition to apoptosis. On the contrary, CD56(bright) NK cells generated after 30 days of culture with FLT3-L plus IL-15 did not show a considerable apoptosis, nevertheless only a subset of these cells expressed granzyme-B, perforin, LFA-1, and CD94-CD159a heterodimer, indicating a functional immaturity. Interestingly, further 15 days of culture with IL-21 plus IL-15 did not induce the generation of CD56(dim) cells from the CD56(bright) subset and actually inhibited IL-15-induced maturation/activation of this latter subset. In fact, IL-15 alone upregulated granzyme-B, TRAIL, Fas ligand, CD94-CD159a, LFA-1, CD16, KIRs, and TRAIL-R2 on CD56(bright) NK cells. Our results suggest that during differentiation CD56(bright) NK cells, similarly to mature activated NK cells, become highly cytotoxic and are relatively resistant to apoptosis induced by TNF family members., (Copyright © 2012 International Society for Advancement of Cytometry.)

Erythropoiesis occurs in bone marrow and it has been shown that during in vivo erythroid differentiation some immature erythroblasts undergo apoptosis. In this regard, it is known that immature erythroblasts are FasL- and TRAIL-sensitive and can be killed by cells expressing these ligand molecules. In the present study, we have investigated the cell death phenomenon that occurs during a common unilineage model of erythroid development. Purified CD34+ human haemopoietic progenitors were cultured in vitro in the presence of SCF, IL-3 and erythropoietin. Their differentiation stages and apoptosis were followed by multiple technical approaches. Flow cytometric evaluation of surface and intracellular molecules revealed that glycophorin A appeared at day 3-4 of incubation and about 75% of viable cells co-expressed high density glycophorin A (Gly(bright)) and adult haemoglobin at day 14 of culture, indicating that this system reasonably recapitulates in vivo normal erythropoiesis. Interestingly, when mature (Gly(bright)) erythroid cells reached their higher percentages (day 14) almost half of cultured cells were apoptotic. Morphological studies indicated that the majority of dead cells contained cytoplasmic granular material typical of basophilic stage, and DNA analysis by flow cytometry and TUNEL reaction revealed nuclear fragmentation. These observations indicate that in vitro unilineage erythroid differentiation, as in vivo, is associated with apoptotic cell death of cells with characteristics of basophilic erythroblasts. We suggest that the interactions between different death receptors on immature basophilic erythroblasts with their ligands on more mature erythroblasts may contribute to induce apoptosis in vitro., (Copyright 2004 Kluwer Academic Publishers)