Dataset Information

Impaired flickering of the permeability transition pore causes SPG7 spastic paraplegia.

ABSTRACT:

Background

Mutations of the mitochondrial protein paraplegin cause hereditary spastic paraplegia type 7 (SPG7), a so-far untreatable degenerative disease of the upper motoneuron with still undefined pathomechanism. The intermittent mitochondrial permeability transition pore (mPTP) opening, called flickering, is an essential process that operates to maintain mitochondrial homeostasis by reducing intra-matrix Ca²⁺ and reactive oxygen species (ROS) concentration, and is critical for efficient synaptic function.

Methods

We use a fluorescence-based approach to measure mPTP flickering in living cells and biochemical and molecular biology techniques to dissect the pathogenic mechanism of SPG7. In the SPG7 animal model we evaluate the potential improvement of the motor defect, neuroinflammation and neurodegeneration by means of an mPTP inducer, the benzodiazepine Bz-423.

Findings

We demonstrate that paraplegin is required for efficient transient opening of the mPTP, that is impaired in both SPG7 patients-derived fibroblasts and primary neurons from Spg7^-/- mice. We show that dysregulation of mPTP opening at the pre-synaptic terminal impairs neurotransmitter release leading to ineffective synaptic transmission. Lack of paraplegin impairs mPTP flickering by a mechanism involving increased expression and activity of sirtuin3, which promotes deacetylation of cyclophilin D, thus hampering mPTP opening. Pharmacological treatment with Bz-423, which bypasses the activity of CypD, normalizes synaptic transmission and rescues the motor impairment of the SPG7 mouse model.

Interpretation

mPTP targeting opens a new avenue for the potential therapy of this form of spastic paraplegia.

Funding

Telethon Foundation grant (TGMGCSBX16TT); Dept. of Defense, US Army, grant W81XWH-18-1-0001.

SUBMITTER: Sambri I

PROVIDER: S-EPMC7553352 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:AimsThe chemotherapy drug doxorubicin (Dox) is commonly used for treating a variety of human cancers; however, it is highly cardiotoxic and induces heart failure. We previously reported that the Bcl-2 mitochondrial death protein Bcl-2/19kDa interaction protein 3 (Bnip3), is critical for provoking mitochondrial perturbations and necrotic cell death in response to Dox; however, the underlying mechanisms had not been elucidated. Herein, we investigated mechanism that drives Bnip3 gene activation and downstream effectors of Bnip3-mediated mitochondrial perturbations and cell death in cardiac myocytes treated with Dox.Methods and resultsNuclear factor-κB (NF-κB) signalling, which transcriptionally silences Bnip3 activation under basal states in cardiac myocytes was dramatically reduced following Dox treatment. This was accompanied by Bnip3 gene activation, mitochondrial injury including calcium influx, permeability transition pore (mPTP) opening, loss of nuclear high mobility group protein 1, reactive oxygen species production, and cell death. Interestingly, impaired NF-κB signalling in cells treated with Dox was accompanied by protein complexes between Bnip3 and cyclophilin D (CypD). Notably, Bnip3-mediated mPTP opening was suppressed by inhibition of CypD-demonstrating that CypD functionally operates downstream of Bnip3. Moreover, restoring IKKβ-NF-κB activity in cardiac myocytes treated with Dox suppressed Bnip3 expression, mitochondrial perturbations, and necrotic cell death.ConclusionsThe findings of the present study reveal a novel signalling pathway that functionally couples NF-κB and Dox cardiomyopathy to a mechanism that is mutually dependent upon and obligatorily linked to the transcriptional control of Bnip3. Our findings further demonstrate that mitochondrial injury and necrotic cell death induced by Bnip3 is contingent upon CypD. Hence, maintaining NF-κB signalling may prove beneficial in reducing mitochondrial dysfunction and heart failure in cancer patients undergoing Dox chemotherapy.