The effect of Boophone disticha on the regulation of Brain Derived Neurotrophic Factor gene expression in BALB/c mouse model of depression
Abstract
The mental disorder of depression ranks high amongst heterogeneous and disabling conditions
on earth. As a complex disease, depression can be characterized by combinations of genetic
and environmental factors. The current antidepressants come with adverse side effects and
exert their therapeutic action only after prolonged treatment, as a consequence, the significance
of developing faster-acting antidepressants cannot be overemphasized. The phytochemical
analysis of Boophone disticha has shown to possess alkaloids, an abundance of alkaloids in the
leave extracts of the plant contributes to its therapeutic abilities, possibly through interactions of
the alkaloids (buphanamine and buphanidrine) to selective serotonin reuptake inhibitor (SSRI)
site of the transporter of serotonin having high affinity for SERT.The brain-derived neurotrophic
factor (BDNF) is a well-studied neurotrophic factor that is responsible for maintaining neurons
and regulating synaptic . The complex gene structure of BDNF, located on chromosome 11 of
the human genome, is regulated by multiple promoters. Strong evidence showed that low
expression of BDNF can be associated with depression prognosis in patient/animal models.
Interestingly, up-regulation of BDNF expression has been seen in response to depression
treatment by antidepressants. Also, epigenetic modulation of BDNF gene and its receptor TrkB
has been shown to alter BDNF expression profiles. Additionally, chromatin remodelling through
acetylation and deacetylation plays an important role in brain associated conditions, with
deacetylation resulting in repression of gene expression. histone deacetylase (HDAC), a form of
chromatin remodelling is speculated to decrease histone acetylation at the BDNF promoters.
The precise promoter responsible for BDNF expression on the onset of depression and
response to treatment is yet to be elucidated. Furthermore, the molecular mechanism of
epigenetic modulation of BDNF and its association with HDAC is yet to be unravelled. This
study, therefore, suggested that the therapeutic benefits of Boophone disticha, ubiquitous plant
widely used by indigenous people to treat ailments such as depression and anxiety, could be
attributed to regulation of BDNF expression, impacting its activity and association with
HDAC.Brain tissue obtained from 60 depressed/ and normal (healthy) male BALB/c mice
representing the B .disticha, fluoxetine, non-gavage and normal treatments were used to study
the gene expression of five promoters (1-5) of BDNF and HDAC5 using RT-qPCR. The nongavage
representing group subjected to the force swim model was the positive control group for
depression and the normal group represented by mice not subjected to force swim served as
negative control (normal). The experimental group comprised of mice treated with B. disticha.
Changes in the expression profiles of BDNF promoter 1-5 and HDAC were measured in relation
to GAPDH using RT-qPCR. Furthermore, methylation specific PCR (MS-PCR) was used to
assess the regulation and/or the methylation status of promoter 4 of BDNF which has been
described known to be regulated by epigenetics and also the protein expression profiles of
BDNF in control and experimental mice were evaluated by ELISA and western blot techniques.It
was found that in the fluoxetine (currently prescribed antidepressant) treated mice, BDNF was
significantly up-regulated (>2-fold in all promoters), gene and protein levels. This is in contrast
to the non-gavage mice, where down-regulation of BDNF was seen. While the 50% methanol
and 50% water leaf extracts of B. disticha treatment was also successful in up-regulating BDNF
in comparison to the non-gavage, but it did not have a similar effect to fluoxetine. The plant
extracts up-regulated the relative expression levels of HDAC5 in relation to fluoxetine and the
normal treatment. The observed gene expression of BDNF was correlated to protein expression
wherein it was found that fluoxetine treatment enhanced the expression of BDNF protein in
comparison to B. disticha.This study found variable promoter activities of BDNF in normal mice
and also showed that treatment (fluoxetine and B. disticha) enhanced BDNF expression.
However, the variable expression in normal mice indicates that this neurotrophic factor would
not serve the therapeutic agent potential significantly. However, BDNF could be thought of as a
marker that represents that an individual is responding to antidepressants due to its enhanced
expression following treatment.