Nerve Growth Factor, Brain-Derived Neurotrophic Factor and Osteocalcin Gene Relationship in Energy Regulation, Bone Homeostasis and Reproductive Organs Analyzed by mRNA Quantitative Evaluation and Linear Correlation Analysis.

Claudia Camerino,Domenico Tricarico,Roberta Caloiero,Elena Conte,Maria Cannone,Adriano Fonzino

doi:10.3389/fphys.2016.00456

Abstract

Nerve Growth Factor (NGF)/Brain-derived Neurotrophic Factor (BDNF) and osteocalcin share common effects regulating energy, bone mass, reproduction and neuronal functions. To investigate on the gene-relationship between NGF, BDNF, and Osteocalcin we compared by RT-PCR the transcript levels of Ngf, Bdnf and Osteocalcin as well as of their receptors p75NTR/NTRK1, NTRK2, and Gprc6a in brain, bone, white/brown adipose tissue (WAT/BAT) and reproductive organs of 3 months old female and male mice. Brain and bone were used as positive controls for NGF/BDNF and Osteocalcin respectively. The role of oxitocin(Oxt) and its receptor(Oxtr) was also investigated. Ngf expression shows an opposite trend compared to Bdnf. Ngf /p75NTR expression is 50% higher in BAT than brain, in both genders, but lower in bone. In contrast, Bdnf expression in bone is higher than in brain, but low in BAT/WAT. We found Osteocalcin gene expressed in brain in both genders, but Gprc6a expression is low in brain and BAT/WAT. As expected, Gprc6a gene is expressed in bone. Oxt gene was markedly expressed in brain, Oxtr in the ovaries and in fat and bone in both genders. Ngf is highly expressed in reproductive tissues and p75NTR mRNA levels are respectively 300, 100, and 50% higher in testis/ovaries/uterus than in brain. In contrast, BDNF genes are not expressed in reproductive tissues. As expected, Gprc6a is expressed in testis but not in the ovaries/uterus. A significant correlation was found between the expression levels of the gene ligands and their receptors in brain, BAT and testis suggesting a common pathway of different genes in these tissues in either male and female. Changes in the expression levels of osteocalcin, Ngf, or Bdnf genes may mutually affect the expression levels of the others. Moreover, it may be possible that different ligands may operate through different receptor subtypes. Oxt and Oxtr failed to show significant correlation. The up-regulation of Ngf /p75NTR in BAT is consistent with NGF as an energy regulator and with BDNF regulating bone.

Highlights

Using bone data as positive control for osteocalcin gene and its receptor Gprc6a, we found that osteocalcin gene was markedly expressed in brain and less in white adipose tissue (WAT) and brown adipose tissue (BAT) and reproductive organs, in both male and female mice (Figure 1)
We found that the mRNA levels of nerve growth factor (Ngf) and nerve growth factor receptor (Ngfr) genes were markedly elevated in BAT other than in brain in either female and male mice (Figure 3)
We found a significant linear correlation between the expression levels of the hormone genes bone gamma-carboxyglutamate protein 3 (Bglap)-Nerve Growth Factor (NGF)-Brain-derived Neurotrophic Factor (BDNF) and their receptors Gprc6a-Ngfr/Ntrk1-Ntrk2 in brain and BAT in either male and female

Summary

Introduction

The actions of osteocalcin, BDNF and NFG and Oxt are related to the regulation of reproduction, energy and bone homeostasis (Camerino, 2009a,b; Karsenty, 2011; Camerino et al, 2012). The uncarboxylated osteocalcin acts as an hormone and promotes insulin secretion and sensitivity (Fulzele et al, 2010; Karsenty, 2011; Oury et al, 2011). The uncarboxylated form of osteocalcin crosses the blood brain barrier (BBB) binds to neurons of the brainstem, midbrain, and hippocampus, enhances the synthesis of monoamine neurotransmitters, inhibits GABA synthesis, prevents anxiety and depression, and favors learning and memory independently of its metabolic functions in mice (Ferron et al, 2010; Oury et al, 2013)

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Results

Conclusion