Final Report Summary - NOGORISE (The Nogo-A receptor complex after CNS injury and its role in the developing and adult nervous system)
Nerve fiber growth in the adult brain and spinal cord for regeneration of injured fibers or compensatory formation of new circuits in response to an injury is very limited in adult humans and mammals. Factors inhibiting nerve fiber growth are a key reason for this situation. A key inhibitory factor for axonal regeneration in the adult brain and spinal cord is the membrane protein Nogo-A. Inactivation of Nogo-A, e.g. by neutralizing antibodies, in animal models of spinal cord injury, brain injury or stroke leads to improved functional recovery in parallel with long distance regeneration of injured fibers and enhanced compensatory nerve fiber growth and new circuit formation. Nogo-A acts via specific membrane receptors. Only one of several Nogo-A receptors could be identified in the past. In this project we have found that the membrane protein Sphingosine 1-phosphate receptor-2 (S1PR2) binds the N-terminal active site of Nogo-A with high affinity. Pharmacological blockers or genetic deletion of S1PR2 abolished the typical Nogo-A effects in tissue culture. In the animal, pharmacological blockade or genetic deletion of S1PR2 enhanced memory and regenerative nerve fiber growth after injury. These results strongly suggest that S1PR2 acts as a functional receptor for Nogo-A mediating its nerve fiber growth inhibitory and synapse modifying actions.
Detailed biochemical analyses showed that the membrane protein tetraspanin-3 can also bind Nogo-A. It acts as a co-receptor and ‘helper’ to trigger Nogo-A intracellular signaling and effects. Surprisingly, we discovered an additional functional Nogo-A receptor, the heparin-sulfate proteoglycans syndecan-3/4, which mediated Nogo-A effects in particular cell types. All these findings provide new insights into the molecular mechanism of action of Nogo-A which regulates nerve fiber growth inhibition and synapse modification by defined multi-subunit receptor complexes.
In the intact adult brain and spinal cord Nogo-A was initially found in the insulating myelin sheath of the nerve fibers. Interestingly, the protein and its receptors are also present at synapses, in particular in the hippocampus or the motor cortex. Treatment of rat cortex slices with function-blocking antibodies against Nogo-A or with Nogo receptor blocking reagents enhanced the activity-dependent strengthening of the synapses (the so called long-term potentiation), a basic mechanism of memory formation. Suppression of Nogo-A also resulted in greater formation of new synapses as revealed by in vivo two-photon microscopy. When rats were trained on a skilled forelimb reaching task while receiving anti-Nogo-A antibodies, learning of this cortically controlled precision movement was improved. These results demonstrate that Nogo-A is also an influential molecular modulator of synaptic plasticity, learning and memory formation.
The effects of anti-Nogo-A antibodies were also studied in a rat model of large cortical strokes. Very similar to such strokes in humans, this lesion destroyed the fine motor control of the affected side of the body, including the forelimb, permanently. Two weeks of anti-Nogo-A immunotherapy followed by two weeks of intense rehabilitative training of skilled forelimb movements resulted in a nearly full recovery of forelimb functions. Anatomically, fibers from the intact side of the forebrain cortex grew over the spinal cord midline and adopted the control over the denervated side of the body. Pharmacogenetic experiments confirmed the crucial role of these newly grown, side-switched fibers for the restored forelimb function.
The results obtained in this five year project contribute important new knowledge to the molecular and physiological understanding of nerve fiber growth inhibitory factors, their receptors and their mechanisms of action in the brain and spinal cord. They were crucial for the start of the currently ongoing clinical trials to enhance recovery after spinal cord injury and stroke in patients by anti-Nogo-A antibodies.
Detailed biochemical analyses showed that the membrane protein tetraspanin-3 can also bind Nogo-A. It acts as a co-receptor and ‘helper’ to trigger Nogo-A intracellular signaling and effects. Surprisingly, we discovered an additional functional Nogo-A receptor, the heparin-sulfate proteoglycans syndecan-3/4, which mediated Nogo-A effects in particular cell types. All these findings provide new insights into the molecular mechanism of action of Nogo-A which regulates nerve fiber growth inhibition and synapse modification by defined multi-subunit receptor complexes.
In the intact adult brain and spinal cord Nogo-A was initially found in the insulating myelin sheath of the nerve fibers. Interestingly, the protein and its receptors are also present at synapses, in particular in the hippocampus or the motor cortex. Treatment of rat cortex slices with function-blocking antibodies against Nogo-A or with Nogo receptor blocking reagents enhanced the activity-dependent strengthening of the synapses (the so called long-term potentiation), a basic mechanism of memory formation. Suppression of Nogo-A also resulted in greater formation of new synapses as revealed by in vivo two-photon microscopy. When rats were trained on a skilled forelimb reaching task while receiving anti-Nogo-A antibodies, learning of this cortically controlled precision movement was improved. These results demonstrate that Nogo-A is also an influential molecular modulator of synaptic plasticity, learning and memory formation.
The effects of anti-Nogo-A antibodies were also studied in a rat model of large cortical strokes. Very similar to such strokes in humans, this lesion destroyed the fine motor control of the affected side of the body, including the forelimb, permanently. Two weeks of anti-Nogo-A immunotherapy followed by two weeks of intense rehabilitative training of skilled forelimb movements resulted in a nearly full recovery of forelimb functions. Anatomically, fibers from the intact side of the forebrain cortex grew over the spinal cord midline and adopted the control over the denervated side of the body. Pharmacogenetic experiments confirmed the crucial role of these newly grown, side-switched fibers for the restored forelimb function.
The results obtained in this five year project contribute important new knowledge to the molecular and physiological understanding of nerve fiber growth inhibitory factors, their receptors and their mechanisms of action in the brain and spinal cord. They were crucial for the start of the currently ongoing clinical trials to enhance recovery after spinal cord injury and stroke in patients by anti-Nogo-A antibodies.