Calcineurin A beta deficiency ameliorates HFD-induced hypothalamic astrocytosis in mice

Katrin Pfuhlmann,Paul T Pfluger,Emily Violette Baumgart,Sonja C Schriever,Luke Harrison,Dhiraj G Kabra,Cristina Garcia-Caceres,Peter Baumann,Matthias H Tschöp,Beata Legutko

doi:10.1186/s12974-018-1076-x

Abstract

ᅟAstrocytosis is a reactive process involving cellular, molecular, and functional changes to facilitate neuronal survival, myelin preservation, blood brain barrier function and protective glial scar formation upon brain insult. The overall pro- or anti-inflammatory impact of reactive astrocytes appears to be driven in a context- and disease-driven manner by modulation of astrocytic Ca2+ homeostasis and activation of Ca2+/calmodulin-activated serine/threonine phosphatase calcineurin. Here, we aimed to assess whether calcineurin is dispensable for astrocytosis in the hypothalamus driven by prolonged high fat diet (HFD) feeding.Global deletion of calcineurin A beta (gene name: Ppp3cb) led to a decrease of glial fibrillary acidic protein (GFAP)-positive cells in the ventromedial hypothalamus (VMH), dorsomedial hypothalamus (DMH), and arcuate nucleus (ARC) of mice exposed chronically to HFD. The concomitant decrease in Iba1-positive microglia in the VMH further suggests a modest impact of Ppp3cb deletion on microgliosis. Pharmacological inhibition of calcineurin activity by Fk506 had no impact on IBA1-positive microglia in hypothalami of mice acutely exposed to HFD for 1 week. However, Fk506-treated mice displayed a decrease in GFAP levels in the ARC. In vivo effects could not be replicated in cell culture, where calcineurin inhibition by Fk506 had no effect on astrocytic morphology, astrocytic cell death, GFAP, and vimentin protein levels or microglia numbers in primary hypothalamic astrocytes and microglia co-cultures. Further, adenoviral overexpression of calcineurin subunit Ppp3r1 in primary glia culture did not lead to an increase in GFAP fluorescence intensity.Overall, our results point to a prominent role of calcineurin in mediating hypothalamic astrocytosis as response to acute and chronic HFD exposure. Moreover, discrepant findings in vivo and in cell culture indicate the necessity of studying astrocytes in their “natural” environment, i.e., preserving an intact hypothalamic microenvironment with neurons and non-neuronal cells in close proximity.

Highlights

Astrocytes represent a population of specialized glial cells with important regulatory functions in the Central nervous system (CNS)
Global loss of Ppp3cb prevents an increase of GFAPpositive astrocytes in the hypothalamus in response to high fat diet (HFD) feeding We recently showed that mice lacking the calcineurin subunit A beta were protected from diet-induced obesity (DIO) [21]
We aimed to assess whether calcineurin ablation affects the activation of astrocytes in mice chronically exposed to HFD

Summary

Introduction

Astrocytes represent a population of specialized glial cells with important regulatory functions in the CNS. Astrocytes are located at the interface between neurons and blood vessels [1], where they facilitate the transfer of Astrocytes can develop a reactive phenotype termed astrocytosis or astrogliosis characterized by a hypertrophy of the soma and cellular processes associated. Astrocytosis occurs in brain injuries reflecting healing processes [7] and pathophysiologic conditions, and in response to high fat diet feeding [8, 9]. HFD-induced astrocytosis is often found in the hypothalamus, a major center for the control of energy and glucose homeostasis, and associated with an increase in HFD-induced inflammation [10,11,12] and microglia activation [13,14,15,16]. How exactly HFD-induced astrocytosis is linked with hypothalamic inflammation and microglial activation remains elusive

Objectives

Methods

Results

Conclusion