Abstract
The astroglial scar is a defining hallmark of secondary pathology following central nervous system (CNS) injury that, despite its role in limiting tissue damage, presents a significant barrier to neuroregeneration. Neural progenitor cell (NPC) therapies for tissue repair and regeneration have demonstrated favorable outcomes, the effects of which are ascribed not only to direct cell replacement but trophic support. Cytokines and growth factors secreted by NPCs aid in modifying the inhibitory and cytotoxic post-injury microenvironment. In an effort to harness and enhance the reparative potential of NPC secretome, we utilized the multifunctional and pro-regenerative cytokine, hepatocyte growth factor (HGF), as a cellular preconditioning agent. We first demonstrated the capacity of HGF to promote NPC survival in the presence of oxidative stress. We then assessed the capacity of this modified conditioned media (CM) to attenuate astrocyte reactivity and promote neurite outgrowth in vitro. HGF pre-conditioned NPCs demonstrated significantly increased levels of tissue inhibitor of metalloproteinases-1 and reduced vascular endothelial growth factor compared to untreated NPCs. In reactive astrocytes, HGF-enhanced NPC-CM effectively reduced glial fibrillary acidic protein (GFAP) expression and chondroitin sulfate proteoglycan deposition to a greater extent than either treatment alone, and enhanced neurite outgrowth of co-cultured neurons. in vivo, this combinatorial treatment strategy might enable tactical modification of the post-injury inhibitory astroglial environment to one that is more conducive to regeneration and functional recovery. These findings have important translational implications for the optimization of current cell-based therapies for CNS injury.
Highlights
Through a non-viral and cost-effective approach, we show that combinatorial treatment using hepatocyte growth factor (HGF)-preconditioning or concurrent administration of HGF alongside Neural progenitor cell (NPC)-conditioned media (CM) effectively attenuates astrocyte reactivity and promotes neurite outgrowth to a greater degree than either treatment alone
We further investigated whether concurrent treatment of NPCs with HGF protein conferred protection against H2O2induced apoptosis
While we did not observe any significant increases in neurite outgrowth following Neural stem/progenitor cell conditioned media (NPC-CM) treatment, numerous studies have demonstrated an upregulation of neurotrophic factors such as brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), glial-derived neurotrophic factor (GDNF), and NGF, all of which may mediate attenuation of glial scar formation and axonal growth (Lu et al, 2003; Chu et al, 2004; Ziv et al, 2006)
Summary
Despite major advances in the medical management and pathophysiological understanding of the central nervous system (CNS), traumatic brain injury (TBI) and spinal cord injury (SCI) remain major causes of death and impairment worldwide, carrying significant personal and socioeconomic ramifications and relatively few treatment options available (Kraus, 1996; Hyder et al, 2007; Cripps et al, 2011; Krueger et al, 2013; Najem et al, 2018).CNS injury is a biphasic and dynamic event characterized by the primary injury, or mechanical insult, followed by a cascade of cellular and molecular events constituting the secondary injury phase. The primary injury predominately results in extensive tissue necrosis and vascular disruption, with the secondary injury further exacerbating cellular apoptosis, vascular disruption, as well as oxidative stress, neuroinflammation, and reactive astrogliosis (Kraus, 1996; Najem et al, 2018). This cascade of injury is well characterized in animal models of TBI and SCI, and faithfully recapitulates many clinical aspects of these injuries (Hellewell et al, 2016; Forgione et al, 2017). Reactive astrocytes undergo molecular changes, most notably an increase in expression of cytoskeletal filaments like glial fibrillary acidic protein (GFAP) as well as increased deposition of growth-inhibitory molecules such as chondroitin sulfate proteoglycans (CSPGs; Mckeon et al, 1995; McKeon et al, 1999; Fitch and Silver, 1997, 2008)
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