www.excemed.org

IMPROVING THE PATIENT’S LIFE THROUGH

MEDICAL EDUCATION

2014 Pre LACTRIMS conference on progressive MS

26 November 2014 - Lima, Perù

2

Private funding

Novartis, Biogen, Merck KGaA

Public funding

MINECO, CIBERNED, Gobierno Vasco

Faculty disclosure

Universidad del País Vasco /Euskal Herriko Unibertsitatea

Carlos Matutee-mail: carlos.matute@ehu.es

Mitochondrial alterations in Multiple Sclerosis

Outline:

• An introduction to mitochondria, the cell powerhouse

• Oligodendrocytes supply lactate to myelinated axons

• Excitotoxicity in oligodendrocytes damages mitochondria

• Mitochondrial defects in MS: neurons, axons and oligodendrocytes

Oxidative phosphorylation

Intermediate metabolism

Ca2+ homeostasis

Mitochondria: a multi-functional organelle

Apoptosis

Mitochondrial function relevance in white matter

• In white matter: axons & oligodendrocytes rely on mitochondrial function to support neurotransmission

• In oligodendrocytes, mitochondrial function is essential for viability and myelin synthesis (Acetyl-CoA)

• In astrocytes, ATP is critical for the control of glutamate metabolism

• Axons → High energy demand (primarily ATP)

• N-acetylaspartate (NAA)– Neuronal integrity marker– Synthesized in neuronal mitochondria– Converted to acetate by oligodendrocytes for myelin synthesis

Three main mitochondrial homeostatic disruptions

1. Energy failure: [ATP]↓↓

2. Oxidative Stress: ROS > antioxidant systems

3. Ca2+ overload

Central features of all neurodegenerative disorders

Physiologycal

Pathological

Saab et al (2013) Curr Op Neurobiol

Myelin supplies energy substrates to axons

submitted

Oligodendroglial NMDA receptors regulate axonal energy metabolism

Demyelination impairs energy supply to axons

Models of Disease Pathogenesis in Multiple Sclerosis

Hauser and Oksenberg 2006 Neuron

ATP

Demyelination, oligodendrocyte death, axonal damage, neuronal loss, atrophy

Glutamate and ATP in excess is toxic to oligodendrocytes and myelin

MBP TUNEL

CNPase CNPase

Matute 1998 PNAS USA

Glutamate levels are elevated in multiple sclerosis

Magnetic resonance spectroscopy at 3 T astrogliosis

Srinivasan et al 2005 Brain

Glutamate and ATP toxicity in oligodendrocytes

PI – dead cells

KAINATE or ATPCONTROL

FDA – live cells

Matute et al 1997 PNAS USA

CELL DEATH

ROS AIF

Nucleus

DNA fragmentation

PARP-1

Procaspase 8

t-Bid

Caspase 3,6,7

Caspase 8

FADD

Bid

AMPA-RVGCC

Na+Ca2+

m Bcl-2

Cyt c

Apaf-1

Caspase 9

CdP

P P P

Bad Bad

14-3-3

Bcl-xl

KAINATE-R

[Ca2+]i

Ca2+

VGCC

Calpain

Bax

Sánchez-Gómez et al. J Neurosci 2003Sánchez-Gómez et al., J Neurosci, 2011

Mitochondria at the crossroads of excitotoxicity in oligodendrocytes

Butt, Fern, Matute (2014 ) Glia

Glutamate and ATP signaling are central to MS pathophysiology

Neuroinflammation favors excitotoxic-mediated mitochondrial damage

• Altered glutamate homeostasis induces mitochondrial damage• Presence of high NO: oxidative stress• Myelin loss-induced trophic imbalance

• Expression of mitochondrial respiratory chain complex I, II and III is reduced in MS active lesions and motor cortex

• mtDNA defects associated with MS

• Abnormal intra-axonal mitochondria prior to axon disruption

• Low N-acetyl aspartate levels in acute and chronic lesions and in normal appearing WM

Mitochondrial dysfunctions in MS

Franklin y Ffrench-Constant 2008 Nat Rev Neurosci

Persistent demyelination leads to axonal damage

Atrophy: loss of axons and neurons

Axons transiently adapt to demyelination

Early response to

demyelination

Waxman 2006, Nat Rev Neurosci

Demyelinated axons are more vulnerable to energy failure and therefore to mitochondrial dysfunction → Axonal degeneration in MS

Mitochondrial dysfunction → Energy failure → Na+ / K + ATPase↓ → Depolarization → sustained Na+ influx → Reverse activity of the Na+ / Ca2+ exchanger → Ca2+ overload → Axonal damage

Non-remyelinated axons ultimately degenerate

Late response to

demyelination

Waxman 2006, Nat Rev Neurosci

Mechanisms of axonal damage during inflammation and demyelination

Waxman 2006, Nat Rev Neurosci

Ca2+ overload in mitochondria initiates axonal failure in MS

Abou-Sleiman et al. 2006 Nat Rev Neurosci

Ca2+ overload and mPTP opening in MS

• Cyclophilin D is a key regulator of the permeability transition pore (mPTP) opening.

• CyPD KO neurons were resistant to oxidative stress and NO, and tolerated higher levels of mitochondrial Ca2+

• CyPD KO-EAE mice partially recovered and preserved axonal integrity.

Forte et al. 2007, PNAS

Conclusions

1. White matter is highly dependent on mitochondrial ATP to propagate electric signals, maintain ionic gradients and facilitate axonal transport

2. Inflammation, oxidative stress and Ca2+ homeostasis disruption lead to mitochondrial dysfunction and energy failure in MS

3. Demyelinated axons in MS lesions are more vulnerable to energy failure and mitochondrial dysfunction

4. ROS and Ca2+ damage axons by inducing mitochondrial mPTP opening.

María DomercqAlberto Pérez SamartínFernando Pérez CerdáFabio CavaliereElena AlberdiVicky Sánchez

Olatz PampliegaOlatz OyangurenEstibaliz EtxeberriaNuria VázquezEstibaliz GonzalezJuan Carlos Chara

Hospital de Basurto, BilbaoAlfredo Rodríguez-Antigüedad

MPI, GöttingenFrank Kirchhoff

AECOM, New YorkEliana Scemes

Universidad del País Vasco, Leioa, Spain

Acknowledgments

Bilbao Guggenheim Museum