TRPV4 disrupts mitochondrial transport and causes axonal degeneration via a CaMKII-dependent elevation of intracellular Ca2+

Brian M Woolums,Alexander R Lau,Hyun Sung,Masashi Tabuchi,Jeremy M Sullivan,Yang Xiang,Pamela C Saavedra-Rivera,Catherine Mamah,Mark N Wu,Yunpeng Yang,Kendra Takle Ruppell,Bryan S Larin,Brett A Mccray,Thomas E Lloyd,William H Aisenberg,Charlotte J Sumner,Douglas N Robinson

doi:10.1038/s41467-020-16411-5

Abstract

The cation channel transient receptor potential vanilloid 4 (TRPV4) is one of the few identified ion channels that can directly cause inherited neurodegeneration syndromes, but the molecular mechanisms are unknown. Here, we show that in vivo expression of a neuropathy-causing TRPV4 mutant (TRPV4R269C) causes dose-dependent neuronal dysfunction and axonal degeneration, which are rescued by genetic or pharmacological blockade of TRPV4 channel activity. TRPV4R269C triggers increased intracellular Ca2+ through a Ca2+/calmodulin-dependent protein kinase II (CaMKII)-mediated mechanism, and CaMKII inhibition prevents both increased intracellular Ca2+ and neurotoxicity in Drosophila and cultured primary mouse neurons. Importantly, TRPV4 activity impairs axonal mitochondrial transport, and TRPV4-mediated neurotoxicity is modulated by the Ca2+-binding mitochondrial GTPase Miro. Our data highlight an integral role for CaMKII in neuronal TRPV4-associated Ca2+ responses, the importance of tightly regulated Ca2+ dynamics for mitochondrial axonal transport, and the therapeutic promise of TRPV4 antagonists for patients with TRPV4-related neurodegenerative diseases.

Highlights

The cation channel transient receptor potential vanilloid 4 (TRPV4) is one of the few identified ion channels that can directly cause inherited neurodegeneration syndromes, but the molecular mechanisms are unknown
The most common form of axonal CMT is caused by mutations of mitofusin 2 (MFN2), which are associated with impaired axonal transport of mitochondria[13,14,15]
Using an unbiased forward genetic screen in Drosophila, we found that TRPV4-mediated increases in intracellular Ca2+ require calmodulin-dependent protein kinase II (CaMKII), revealing a central role for CaMKII in TRPV4associated axonal degeneration

Summary

Introduction

The cation channel transient receptor potential vanilloid 4 (TRPV4) is one of the few identified ion channels that can directly cause inherited neurodegeneration syndromes, but the molecular mechanisms are unknown. Peripheral nerve degeneration in these disorders results in muscle weakness, of limb, diaphragm, and vocal fold muscles, the latter of which can be life threatening. They are strikingly variable in severity, ranging from severe, congenital onset to mild, late adult onset. Investigating how TRPV4 mutations cause peripheral neuropathy provides an opportunity to understand the molecular events linking an ion channel and Ca2+ homeostasis to the process of neurodegeneration. Interrogation of the cellular events underlying TRPV4-associated neuropathy may provide insights into mechanistic links between Ca2+ and impaired axonal transport in neurodegenerative disease

Methods

Results

Conclusion