TGFß1 Stimulates the Over-Production of White Matter Astrocytes from Precursors of the “Brain Marrow” in a Rodent Model of Neonatal Encephalopathy

Abstract

BackgroundIn children born prematurely and those surviving cerebral ischemia there are white matter abnormalities that correlate with neurological dysfunction. Since this injury occurs in the immature brain, when the majority of subventricular zone (SVZ) cells generate white matter oligodendrocytes, we sought to study the effect this injury has on gliogenesis from the SVZ. We hypothesized that there is aberrant glial cell generation from the SVZ after neonatal hypoxia ischemia (H/I) that contributes to an increased astrogliogenesis with concomitant oligodendroglial insufficiency. Mechanistically we hypothesized that an increase in specific locally produced cytokines during recovery from injury were modifying the differentiation of glial progenitors towards astrocytes at the expense of the more developmentally-appropriate oligodendrocytes.Methodology/Principal FindingFor these studies we used the Vannucci H/I rat model where P6 rats are subjected to unilateral common carotid ligation followed by 75 min of systemic hypoxia. Retroviral lineage tracing studies combined with morphological and immunohistochemical analyses revealed the preferential generation of SVZ-derived white matter astrocytes instead of oligodendrocytes post hypoxia/ischemia. Microarray and QRT-PCR analyses of the damaged SVZ showed increased expression of several cytokines and receptors that are known to promote astrocyte differentiation, such as EGF, LIF and TGFß signaling components. Using gliospheres to model the neonatal SVZ, we evaluated the effects of these cytokines on signal transduction pathways regulating astrocyte generation, proliferation and differentiation. These studies demonstrated that combinations of EGF, LIF and TGFß1 reconstituted the increased astrogliogenesis. TGFß1-induced Smad 2/3 phosphorylation and the combination of EGF, LIF and TGFß1 synergistically increased STAT3 phosphorylation over single or double cytokine combinations. Pharmacologically inhibiting ALK5 signaling in vitro antagonized the TGFß1-induced increase in astrocyte generation and antagonizing ALK5 signaling in vivo similarly inhibited astrogliogenesis within the SVZ during recovery from H/I.Conclusion/SignificanceAltogether, these data indicate that there is aberrant specification of glial precursors within the neonatal SVZ during recovery from neonatal H/I that is a consequence of altered cytokine signaling. Our studies further suggest that antagonizing the ALK5 receptor will restore the normal pattern of cell differentiation after injury to the immature brain.

Phenotypically aberrant astrocytes that promote motoneuron damage in a model of inherited amyotrophic lateral sclerosis

“…Such a milieu may promote the recruitment and phenotypic transition of glial cells or precursors (40), leading to the generation of AbA cells. A similar proliferative and immature phenotype of astrocytes can be found following defective function in paired box 6 (Pax6) transcription factor (41) and in pathological conditions leading to aberrant specification of glial precursors (42).…”

Delayed ALK5 inhibition improves functional recovery in neonatal brain injury

“…33 The signals that maintain this chronic neuroinflammation have not been fully established, but TGFb1 is a strong candidate. TGFß1 expression is both delayed and prolonged after brain injury 8,34,35 and several studies have shown that it can stimulate neuroinflammation within the CNS. 14,36 Moreover, over-expression of TGFb1 in the CNS of The integrated optical density (IOD) was determined for MBP and GFAP immunoreactivity in the neocortex, striatum and the corpus callosum (CC) from ipsilateral (IL) and contralateral (CL) hemispheres as well as from shamoperated animals.…”

“…The optimal treatment duration and dosage of SB505124 was established from the experiments summarized in Figure 1, which were predicated upon previously published studies. 8 …”

Mechanisms of Mouse Neural Precursor Expansion after Neonatal Hypoxia-Ischemia

“…The rat SVZ is known to expand in size during acute recovery from neonatal H-I with an increase in tripotential NPs (Felling et al, 2006;Yang and Levison, 2006;Alagappan et al, 2009) that is followed at later time points with an increase in the production of new neuroblasts, neurons, astrocytes, oligodendrocyte precursors, and oligodendrocytes (although the latter are rarer; Back et al, 2002;Plane et al, 2004;Zaidi et al, 2004;Ong et al, 2005;Yang and Levison, 2007;Yang et al, 2008;Bain et al, 2010;Dizon et al, 2010). However, it has not been clear with any level of precision which NPs are expanding after H-I and which injury signals are necessary for their expansion.…”