Abstract
Macrophages play a key role in triggering and regulation of neuroregeneration. The characteristic feature of macrophages is pronounced plasticity, which manifests itself in the ability of macrophages to change their functional phenotype depending on the micromilieu. Apoptotic cell clearance (efferocytosis) is an important inducer of a macrophage polarization to M2 phenotype under pathological settings. Previously, we have developed an original protocol for the generation of M2-like macrophages, polarized by efferocytosis under serum-deprived conditions (M2 (LS), Low Serum). The present study was aimed to assess a neuroregenerative potential of M2 (LS) macrophages. We studied their effect on the differentiation of SH-SY5Y cells in comparison with retinoic acid (RA). As the morphological criteria of differentiation we have assessed the relative content of differentiated cells, i.e., cells with a neurite length exceeding the cell body length, and the average neurite length on days 3, 7, and 13. The ratio of neuron-like (N-type) and epithelial-like (S-type) cells in cultures was also assessed. SH-SY5Y cells were characterized by a low level of spontaneous differentiation, both under standard conditions (10% FBS) and serum deprivation (1% FBS). Upon RA treatment, SH-SY5Y cells stopped proliferating and underwent neuronal differentiation. Cultivation of SH-SY5Y cells in the presence of M2 (LS) conditioned medium also led to a significant increase in the relative content of differentiated cells, the average length of neurite-like processes, as well as a change in the balance of S- and N-type cells towards a pronounced predominance of the latter. The morphological features of differentiation were significantly less pronounced at early stage (day 3) of differentiation as compared with the RA-induced changes and reached the level of positive control only at later stages (day 13) (p < 0.05). In contrast to retinoic acid, M2 (LS) conditioned medium induced neuronal differentiation of SH-SY5Y cells without suppressing their proliferative activity. The data obtained may indicate a high neuroregenerative potential of M2 macrophages in vitro, which is realized through soluble factors and manifests itself in promoting SH-SY5Y differentiation.
Highlights
Macrophages (Ms), being an essential component of innate immunity, play a key role in inflammation, regeneration, and homeostasis maintenance
We have developed an original protocol for the M2-like Ms generation based on the culture of human blood monocytes under serum-deprived conditions, which contributes to the development of deprivation apoptosis with the subsequent engulfment of apoptotic cells by macrophages
The Ms obtained in this way are characterized by low antigen-presenting and proinflammatory acti vities as well as a high level of growth and neurotro phic factors secretion (VEGF, IGF-1, EPO, brain derived neurotrophic factor (BDNF), EGF, FGF-basic) [3, 22]
Summary
Macrophages (Ms), being an essential component of innate immunity, play a key role in inflammation, regeneration, and homeostasis maintenance. The Ms obtained in this way are characterized by low antigen-presenting and proinflammatory acti vities as well as a high level of growth and neurotro phic factors secretion (VEGF, IGF-1, EPO, BDNF, EGF, FGF-basic) [3, 22]. The combination of these properties allows to consider M2 (LS) as a Ms functional phenotype with a high neuroregenerative potential which was confirmed by pilot clinical trials in patients with CNS pathology [4, 23]. An influence of M2 (LS) on the neural cell differentiation in vitro has not been previously studied
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