elena rugarli convegno mitocon 2015
TRANSCRIPT
Mitochondria and neurons
•High need for Ca++ buffering
•ATP production
•Maintenance of membrane potential
•Release and reuptake of neurotransmitters
Transport to long distance site
Long half-life
Dual activity of the m-AAA protease in mitochondria
Protein degradation
Protein activation
Complete proteolysisto peptides
Protein processing
Nolden et al., Cell 2005
The human m-AAA proteases
IMS
matrix
Hetero-oligomericm-AAA protease
Homo-oligomericm-AAA protease
AFG3L2 AFG3L2 paraplegin
MTS TM AAA PDTM
Hereditary spastic paraplegia and mutations in SPG7/paraplegin
•Autosomal recessive
•Pure forms: weakness and spasticity of the lower limbs
•Complex forms: cerebellar signs, nystagmus, muscular wasting, optic pallor, peripheral neuropathy
AFG3L2 is mutated in spinocerebellar ataxia SCA28 and in a rare form of spastic-ataxia
Loss of balancelimb and gait ataxiaDysarthria
Di Bella et al., Nature Genetics, 2010
Y616C
Heterozygous mutations: SCA28 Homozygous mutation:SPAX5
Early onset spastic gait
Generalized tonic-clonic and myoclonic seizures
Progressive motor degeneration, with dysarthria and dysphagia and complete loss of ambulation.
Ataxia
Pierson et al. PLOS genetics, 2011
What is the pathogenic mechanism underlying neurological diseases linked to mutations in subunits
of the m-AAA protease ?
Mouse models of m-AAA protease subunits
Spg 7 -/-
Ferreirinha et al. J. Clin. Invest., 2004
•Late onset motor phenotype; normal vitality and fertility
•4,5 months: Ultrastructural mitochondria abnormalities in synaptic mitochondria
•7 months: retrograde axon degeneration in long spinal tracts and peripheral nerves
Afg3l2 -/-
Maltecca et al. J. Neurosci., 2008
•Severe phenotype, die at P16.
•Impairment of axonal development with delayed myelination and poor radial growth
•Abnormal mitochondria in neuronal cell bodies
LoxP LoxP
frt
ex1 ex2 ex3 ex6ex5ex4 ex7
LoxP
ex1 ex2 ex3 ex6 ex7
deleted
floxed
L7-Cre
CAMKII-Cre
Afg3l2 deficiency in adult neurons
Deletion of Afg3l2 from Purkinje cells causes neuronal degeneration associated with
neuroinflammation
Early-onset COX deficiency in Purkinje neurons
WT Afg3l2 PC-KO
Combined COX (brown)-SDH (blue) staining
Almajan et al. JCI, 2013
Reduced mitochondrial protein synthesis in Afg3l2-deleted brain mitochondria
Almajan et al. JCI, 2013
BN-PAGE
CII (70kDa)
MRPL32
Brain Liver Heart
wt ko wt kowt ko
Reduced levels of mature MRPL32 in Afg3l2-deficient mice
Almajan et al. JCI, 2013
X
Mito-YFPSTOP
XL7 Cre
Afg3l2 flox/flox
Abnormalities of the mitochondrial network occur very early and before any sign of degeneration
Downregulation of Afg3l2 in primary neurons leads to impaired anterograde transport of
mitochondria
Kondadi et al. EMBO J, 2014
Transport of dysfunctional mitochondria in axons is inhibited
Which is the signal? Is fragmentation causing the transport defect?
A stress pathway affected mitochondrial dynamics
Fusion
Content mixing
Maintenance ofmitochondrial integrity
Fission
Mitochondrial fragmentation
Mitophagy Apoptosis
+
Destabilization ofL-OPA1
Formation ofS-OPA1
Cell survival Cell survival Cell death
OMA1
Loss of Δψm
ATPLack of AFG3L2
Mitochondrial defects in Afg3l2-depleted neurons are independent of OMA1 activation
Kondadi et al. EMBO J, 2014
Deletion of Afg3l2 in adult brain causes neurodegeneration and tau hyperphosphorylation
Sara Montagner
fl/fl fl/fl: CaMKIIa-Cre fl/fl fl/fl: CaMKIIa-Cre
Nissl staining p-tau: AT8
Deletion of Afg3l2 in adult brain causes tau hyperphosphorylation and activation of PKA and ERK
kinases
Kondadi et al. EMBO J, 2014
Tau downregulation partially rescues the mitochondrial transport defects of Afg3l2-depleted neurons
Kondadi et al. EMBO J, 2014
Can modulation of tau affect mitochondrial transport in neurons?
NAC treatment rescues mitochondrial transport defects and decrease phospho-tau level in
primary neurons
Kondadi et al. EMBO J, 2014
AFG3L2 deficiency
ROS
Stress-induced mitochondrial fragmentation mediated by OMA1
respiratory deficiency
Anterograde mitochondrial transport
phospho-tau
ATP levels
Neurodegeneration
?
Impaired mitochondrial protein synthesisReduced assembly of respiratory chain subunits
Eva AlmajanArun Kumar Kondadi
Shuaiyu WangSara MontagnerPaola Martinelli
Esther Barth
Thomas LangerRicarda RichterAnne Korwitz
Nikolai KladtAstrid SchaussCECAD
Nils-Göran Larsson,MPI for ageing research
Acknowledgements
The global dosage of m-AAA proteases is important to prevent neurodegeneration in
the mouse
Developmental axon defects
Late-onset axonal degeneration
Spg7 -/-
Spg7 -/- Afg3l2 -/-
Afg3l2 -/-
Afg3l2 -/+
Late-onset cerebellar dysfunction
Spg7 -/- Afg3l2 -/-
Early-onset neurodegeneration
Embryonic lethal
Ferreirinha et al. J. Clin. Invest., 2004
Maltecca et al. J. Neurosci., 2008
Maltecca et al. J. Neurosci., 2009
Martinelli et al. HMG., 2009
tau mediated neurodegeneration and mitochondria
Yoshiyama Y et al. J Neurol Neurosurg Psychiatry doi:10.1136/jnnp-2012-303144