110
- Chemerin: it is an adipokine associated with obesity and the metabolic syn-
drome, its levels in the bloodstream seems to be highly heritable. It significantly
mediates the formation of blood vessels to a similar extent as vascular endothe-
lial growth factor [ 64 ].5.3 Stem Cells Mobilization
In some papers regarding neoangiogenesis, there is no mention about the role of
endothelial stem cells. Instead, they are talking about activation of endothelial
cells – thus assuming mitotical potential of endothelial cells, both in sprouting and
intussusceptive angiogenesis [ 25 ]. Exercise training activates circulating, as well as
resident tissue-specific cardiac, stem/progenitor cells [ 65 ]. Exercise especially
induces endothelial progenitor cells to proliferate [ 56 , 66 ], migrate and differentiate
into mature endothelial cells, giving rise to endothelial regeneration and angiogen-
esis [ 16 ]. Endothelial progenitor cells are a subtype of circulating stem cells origi-
nally formed in bone marrow, with high proliferative potential, able to differentiate
into mature endothelial cells during the neoangiogenesis at trained people [ 67 ].
Several physiological and pathophysiological stimuli or drugs modulate endothelial
progenitor cell mobilization. Nevertheless, to our knowledge, unequivocal defini-
tion of endothelial progenitor cells is lacking [ 68 ]. In addition to this direct struc-
tural role, endothelial progenitor cells improve neovascularization, also by secreting
numerous pro-angiogenic factors able to enhance the proliferation [ 26 , 69 ].
5.4 Hypoxemia
Findings indicate that lowered oxygen tension may play a role in exercise-induced
angiogenesis in skeletal muscle. One of the possible mediating mechanisms could
be action of angiogenic factors induced by muscle hypoxia during exercise [ 47 , 70 ].
Effect of hypoxemia and the question of mere existence of exercise-induced hypox-
emia remain unknown and unresponded.
6 Conclusion
As a first thought is important to tell, that questions to which we do not know the
answers prevail over those answered and others new are raising as we are trying to
understand molecular signaling pathways and mechanisms behind beneficial effect
of neoangiogenesis within the heart wall. We were reviewing some studies with
similar methodologies and hypotheses, but with completely different outcome
(effect of miRNA-126, VEGF levels after exercise, and so on).
M. Miko and I. Varga