Glial aromatization increases the expression of bone morphogenetic protein‐2 in the injured zebra finch brain

Abstract

Abbreviations used: BMP, bone morphogenetic protein; DEPC, diethylpyrocarbonate; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; IACUC, institutional animal care and use committee; MCAO, middle cerebral artery occlusion; NCBI, national center for biotechnology information; PBS, phosphate buffered saline; sqPCR, semi-quantitative polymerase chain reaction. AbstractIn songbirds, brain injury upregulates glial aromatase. The resulting local estrogen synthesis mitigates apoptosis and enhances cytogenesis by poorly understood mechanisms. Bone morphogenetic proteins (BMPs), long studied for their role in neural development, are also neuroprotective and cytogenic in the adult brain. BMPs remain uncharacterized in songbirds, as do the mechanisms regulating their post-injury expression. We first established the expression of BMPs 2, 4, 6, and 7 in the adult zebra finch brain using RT-PCR. Next, we determined the effect of neural insult on BMP expression, by comparing BMP transcripts between injured and uninjured telencephalic hemispheres using semi-quantitative PCR. The expression of BMPs 2 and 4, but not 6 and 7, increased 24 h post-injury. To determine the influence of aromatase on BMP expression, we compared BMP expression following delivery of the aromatase inhibitor Fadrozole or vehicle into contralateral hemispheres. Fadrozole decreased BMP2, but not BMP4, expression, suggesting that aromatization may induce BMP2 expression following injury. Since BMPs are gliogenic and neurotrophic, future studies will test if the neuroprotective and cytogenic effects of aromatase upregulation are mediated by BMP2. Songbirds may be excellent models towards understanding the role of local estrogen synthesis and its downstream mechanisms on neuroprotection and repair. Keywords: estrogen, gliosis, growth factors, neuroprotection, stroke. Bone morphogenetic proteins (BMPs) are diffusible factors critical for the development of the nervous system in vertebrates (Liu and Niswander 2005). They are also expressed in the adult brain (Charytoniuk et al. 2000;Chen et al. 2003;Peretto et al. 2004) where they influence cell proliferation, survival, and fate, particularly following brain injury (Wang et al. 2001;Chang et al. 2002;Brederlau et al. 2004;Chou et al. 2006;Hampton et al. 2007;Colak et al. 2008). Specifically, BMPs 2, 4, 6, and 7, are upregulated following brain damage in rodents (Chang et al. 2003;Hampton et al. 2007;Liu et al. 2007), and exogenous administration of either BMP 6 or BMP 7 limits degeneration and increases recovery of behavioral function following middle cerebral artery occlusion (MCAO) (Liu et al. 2001;Wang et al. 2001;Chang et al. 2003;Chou et al. 2006). In addition to being neuroprotective, BMPs may also enhance gliogenesis and neurogenesis in the post-injury environment (Chou et al. 2006;Xin et al. 2006). Despite their potential benefits and their endogenous response to insult, however, the mechanisms that upregulate BMPs after brain injury have yet to be elucidated.In non In the zebra finch, injury induced aroma...

A Quantification of the Injury‐Induced Changes in Central Aromatase, Oestrogenic Milieu and Steroid Receptor Expression in the Zebra Finch

“…Given previous studies establishing the involvement of the oestrogen receptors ERa, ERb and GPER-1 in neuroprotection following brain injury (15,16,(18)(19)(20)(22)(23)(24)(25)(26)(27), we were surprised to find no differences in the expression of these receptors in the present experiment. We did, however, observe a significant down-regulation of AR expression in the injured hemisphere compared to the uninjured hemisphere of both male and female zebra finches (Fig.…”

“…Similarly, administration of peripheral E 2 attenuates the increased neuronal damage induced by aromatase inhibition following injury in mice (17). In addition to the mitigation of neuronal damage and secondary degeneration following brain injury, E 2 has also been suggested to enhance neurogenesis after injury (18)(19)(20). The data strongly suggest that the neuroprotective effects of centrally synthesised E 2 are a conserved characteristic across several vertebrates.…”

Effects of Vascular Endothelial Growth Factor 165 on Bone Tissue Engineering

“…Vascularization [17]: Neovascular endothelial cells at the bone defects of remaining specimens were marked by anti-rabbit CD31 antibody. The sections were observed under a high-magnification microscope, and 5 clear fields were selected to calculate the number of microvessels.…”

Intracerebral estrogen provision increases cytogenesis and neurogenesis in the injured zebra finch brain

“…Prior to injury, each bird was anesthetized with 0.03 cc Nembutal (pentobarbital sodium salt from Sigma‐Aldrich, St. Louis, MO, 25 mg/mL in a 20% propylene glycol and 5% ethanol solution). Injuries were made as previously described (Wynne and Saldanha, 2004; Saldanha et al, 2005; Walters and Saldanha, 2008; Wynne et al, 2008). Briefly, animals were placed into a stereotaxic apparatus and given bilateral penetrating injuries using a 50 μL‐22S Hamilton syringe (Hamilton, Reno, NV) that also served as the drug delivery needle.…”