Endoplasmic reticulum chaperone BiP/GRP78 knockdown leads to autophagy and cell death of arginine vasopressin neurons in mice

Yohei Kawaguchi,Yoshihiro Ito,Takeshi Onoue,Valery Grinevich,Shintaro Iwama,Daisuke Hagiwara,Junki Kurimoto,Mariko Sugiyama,Tomoko Kobayashi,Hiroshi Takagi,Hiroshi Arima,Ryoichi Banno,Takashi Miyata,Yuichi Hodai,Hidetaka Suga

doi:10.1038/s41598-020-76839-z

Abstract

The immunoglobulin heavy chain binding protein (BiP), also referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. Our previous studies showed that BiP is expressed in arginine vasopressin (AVP) neurons under non-stress conditions and that BiP expression is upregulated in proportion to the increased AVP expression under dehydration. To clarify the role of BiP in AVP neurons, we used a viral approach in combination with shRNA interference for BiP knockdown in mouse AVP neurons. Injection of a recombinant adeno-associated virus equipped with a mouse AVP promoter and BiP shRNA cassette provided specific BiP knockdown in AVP neurons of the supraoptic (SON) and paraventricular nuclei (PVN) in mice. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Immunoelectron microscopy of AVP neurons revealed that autophagy was activated through the process of AVP neuronal loss, whereas no obvious features characteristic of apoptosis were observed. Pharmacological inhibition of autophagy by chloroquine exacerbated the AVP neuronal loss due to BiP knockdown, indicating a protective role of autophagy in AVP neurons under ER stress. In summary, our results demonstrate that BiP is essential for the AVP neuron system.

Highlights

The immunoglobulin heavy chain binding protein (BiP), referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress
Our data demonstrated that arginine vasopressin (AVP) neuron-specific BiP knockdown leads to ER stress and activates autophagy in AVP neurons followed by AVP neuronal loss
We showed that BiP conditional knockdown in AVP neurons led to dilatation of the ER lumen and upregulation of ER stress markers followed by AVP neuronal loss

Summary

Introduction

The immunoglobulin heavy chain binding protein (BiP), referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Knockout of the Sel1L-Hrd[1] protein complex, a principal ER-resident E3 ligase in mammalian ERAD, is reported to cause marked retention and aggregation of AVP precursors in the ER, resulting in polyuria due to AVP d eficiency[23]. These data indicate that ER protein quality control is essential for appropriate AVP synthesis and release. ER stress has been implicated in the pathophysiology of some genetic types of central diabetes insipidus such as familial neurohypophysial diabetes insipidus (FNDI) which is caused by the accumulation of mutant AVP precursors in the E R24–30

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Conclusion