Post-hypoxic and ischemic neuroprotection of BMP-7 in the cerebral cortex and caudate–putamen tissue of rat

Abstract

Previous reports have indicated that exogenous bone morphogenetic protein-7 (BMP-7) has a neuroprotective effect after cerebral ischemia injury and promotes motor function recovery, but the appropriate BMP-7 concentration and time course are unclear. Here, we assessed endogenous BMP-7 expression in hypoxia and ischemia-damaged brain tissues and investigated the effects of different BMP-7 concentrations in pre- and post-hypoxic primary rat neurons. The results showed that BMP-7 expression was significantly higher in the ischemic hemisphere. The expressions of BMP-7 and caspase-3 were localized in the cytoplasm of the primary cerebral cortical and caudate–putamen neurons 24 h after hypoxia/reoxygenation. After BMP-7 treatment, the number of caspase-3 positive neurons began to decrease with increasing BMP-7 concentrations up to 80 ng/ml, but not beyond. Although the numbers of caspase-3-positive neurons between pre- and post-hypoxia/reoxygenation were not significantly different, more dendrites were observed in the groups treated prior to hypoxia/reoxygenation. These results suggest that increased BMP-7 expression can be induced in the cerebral cortex and caudate–putamen both in vivo and in vitro in hypoxic-ischemic states. The neuroprotective mechanism of BMP-7 may include apoptosis suppression, and its effect was enhanced from 40 to 80 ng/ml. Pre-hypoxic BMP-7 treatment may be useful to stimulate dendrite sprouting in non-injured neurons.

Introduction

Neurodegenerative disease is an important research topic because of its high prevalence and its impact on the quality of life of patients. It is becoming increasingly urgent and essential to find new treatments. One group of proteins that shows promise for clinical treatment is the bone morphogenetic protein (BMP) family. BMPs have been shown to regulate many important processes in the developing nervous system (Horbinski et al., 2002), skeletal system (Nakamura et al., 2011) and viscera (Soares et al., 2008), including the specification of cell fate, neuronal cell differentiation, proliferation, and apoptosis (Bond et al., 2012, Guan et al., 2013), and they may be neuroprotective against cerebral ischemia injury (Chen et al., 2007, Chou et al., 2006). It has been suggested that methamphetamine facilitated cerebral infarction after ischemia possibly mediated, in part, through the suppression of BMP7 (Shen et al., 2008). Intravenous injection or intracisternal delivery of BMP-7 24 h pre- or post-stroke has been shown to enhance behavioral recovery (Chang et al., 2002, Chou et al., 2006, Ren et al., 2000), while it could reduce infarct volumes if administered 24 h before stroke (Lin et al., 1999). In recent years, the application of transgenic technology is also very popular and use of this technique showed that BMP7 could reduce ischemic cell death in mice (Heinonen et al., 2014). These observed differences indicate that BMPs may have both neuroprotective and neuroregenerative properties, and the use of BMP-7 for stroke has high therapeutic potential. Currently, no clinical trials are under way for BMP treatment of stroke; however, recombinant human BMP-7 (bone morphogenetic protein-7) or OP-1 (osteogenic protein-1) have been approved by the U.S. Food and Drug Administration (FDA) for use in clinical trials of spinal fusion surgery and tibial non-union (Friedlaender et al., 2001).

Several studies have shown that the cerebral cortex and caudate–putamen are injured after infarction of the middle cerebral artery (Chen et al., 2007). The aim of the study was to detect the expression of BMP-7 in the cerebral cortex and caudate–putamen 24 h after ischemia/reperfusion and in primary hypoxic neurons to determine whether endogenous BMP-7 has neuroprotective effects in hypoxic-ischemic injured nerve tissue and to provide a baseline for future studies. Due to the sensitivity and vulnerability of brain tissue to hypoxic-ischemic injury and the very low regenerative capacity, the time of hypoxia–ischemia is closely related with the severity of damage. Therefore, identifying the best delivery time of BMP-7 to achieve maximum neuroprotection is important. Here, we focused on the effects of BMP-7 treatment in hypoxia cultured cortical rat neurons, to determine the best time and dose and provide strong evidence for the benefits of early clinical BMP-7 treatment.