Hypoxia-inducible factor (HIF)-1α represents the oxygen-sensitive subunit of HIF transcriptional factor, usually degraded in normoxia and stabilized in hypoxia to regulate several target gene expression. Nevertheless, in the skeletal muscle satellite stem cells (SCs), an oxygen level-independent regulation of HIF-1α has been observed. Although HIF-1α has been highlighted as SC function regulator, its spatio-temporal expression and role during myogenic progression remain controversial. We herein analyzed HIF-1α expression and localization in differentiating murine C2C12 myoblasts and SCs under normoxia and evaluated matrix metalloproteinase (MMP)-9 as a HIF-1α target, by biomolecular, biochemical, morphological and electrophysiological analyses. HIF-1α expression increased after 24/48 h of differentiating culture and tended to decline after 72 h/5 days. Committed and proliferating mononuclear myoblasts exhibited nuclear HIF-1α expression, differently from the more elongated and parallel-aligned cells, likely ready to fuse with each other, which show mainly a cytoplasmic localization of the factor. Multinucleated myotubes displayed both a nuclear and cytoplasmic HIF-1α expression. The MMP-9 and MyoD (myogenic activation marker) expression synchronized with that of HIF-1α, increasing after 24 h of differentiation. Short-interfering RNA silencing of HIF-1α and MMP-9 and MMP-9 pharmacological inhibition unraveled MMP-9 as HIF-1α downstream effector and HIF-1α/MMP-9 axis essential for the morpho-functional cell myogenic commitment.

The term neuroinflammation defines the reactions of astrocytes and microglia to alterations in homeostasis in the diseased central nervous system (CNS), the exacerbation of which contributes to the neurodegenerative effects of Alzheimer's disease (AD). Local environmental conditions, such as the presence of proinflammatory molecules, mechanical properties of the extracellular matrix (ECM) and local cell-cell interactions, are determinants of glial cell phenotypes. In AD, the load of the cytotoxic/proinflammatory amyloid β peptide (Aβ) is a microenvironmental component increasingly growing in the CNS, imposing time-evolving challenges on resident cells. This study aimed at investigating the temporal and spatial variations of the effects produced by this process on astrocytes and microglia, either directly or by interfering in their interactions. Ex vivo confocal analyses of hippocampal sections from the mouse model TgCRND8 at different ages have shown that overproduction of Aβ peptide induced early and time persistent disassembly of functional astroglia syncytium and promoted a senile phenotype of reactive microglia, hindering Aβ clearance. In the late stages of disease, these patterns were altered in the presence of Aβ-plaques, surrounded by typically reactive astrocytes and microglia. Morphofunctional characterization of peri-plaque gliosis revealed a direct contribution of astrocytes in plaque buildup that might result in shielding Aβ-peptide cytotoxicity and, as a side effect, in exacerbating neuroinflammation.