Targeting the TCA cycle can ameliorate widespread axonal energy deficiency in neuroinflammatory lesions.

Inflammation in the central nervous system can impair the function of neuronal mitochondria and contributes to axon degeneration in the common neuroinflammatory disease multiple sclerosis (MS). Here we combine cell-type-specific mitochondrial proteomics with in vivo biosensor imaging to dissect how inflammation alters the molecular composition and functional capacity of neuronal mitochondria. We show that neuroinflammatory lesions in the mouse spinal cord cause widespread and persisting axonal ATP deficiency, which precedes mitochondrial oxidation and calcium overload. This axonal energy deficiency is associated with impaired electron transport chain function, but also an upstream imbalance of tricarboxylic acid (TCA) cycle enzymes, with several, including key rate-limiting, enzymes being depleted in neuronal mitochondria in experimental models and in MS lesions. Notably, viral overexpression of individual TCA enzymes can ameliorate the axonal energy deficits in neuroinflammatory lesions, suggesting that TCA cycle dysfunction in MS may be amendable to therapy.

Synaptogenic gene therapy with FGF22 improves circuit plasticity and functional recovery following spinal cord injury.

Functional recovery following incomplete spinal cord injury (SCI) depends on the rewiring of motor circuits during which supraspinal connections form new contacts onto spinal relay neurons. We have recently identified a critical role of the presynaptic organizer FGF22 for the formation of new synapses in the remodeling spinal cord. Here, we now explore whether and how targeted overexpression of FGF22 can be used to mitigate the severe functional consequences of SCI. By targeting FGF22 expression to either long propriospinal neurons, excitatory interneurons, or a broader population of interneurons, we establish that FGF22 can enhance neuronal rewiring both in a circuit-specific and comprehensive way. We can further demonstrate that the latter approach can restore functional recovery when applied either on the day of the lesion or within 24 h. Our study thus establishes viral gene transfer of FGF22 as a new synaptogenic treatment for SCI and defines a critical therapeutic window for its application.

Coordinated neurostimulation promotes circuit rewiring and unlocks recovery after spinal cord injury.

Functional recovery after incomplete spinal cord injury depends on the effective rewiring of neuronal circuits. Here, we show that selective chemogenetic activation of either corticospinal projection neurons or intraspinal relay neurons alone led to anatomically restricted plasticity and little functional recovery. In contrast, coordinated stimulation of both supraspinal centers and spinal relay stations resulted in marked and circuit-specific enhancement of neuronal rewiring, shortened EMG latencies, and improved locomotor recovery.

A deep learning-based toolbox for Automated Limb Motion Analysis (ALMA) in murine models of neurological disorders.

In neuroscience research, the refined analysis of rodent locomotion is complex and cumbersome, and access to the technique is limited because of the necessity for expensive equipment. In this study, we implemented a new deep learning-based open-source toolbox for Automated Limb Motion Analysis (ALMA) that requires only basic behavioral equipment and an inexpensive camera. The ALMA toolbox enables the consistent and comprehensive analyses of locomotor kinematics and paw placement and can be applied to neurological conditions affecting the brain and spinal cord. We demonstrated that the ALMA toolbox can (1) robustly track the evolution of locomotor deficits after spinal cord injury, (2) sensitively detect locomotor abnormalities after traumatic brain injury, and (3) correctly predict disease onset in a multiple sclerosis model. We, therefore, established a broadly applicable automated and standardized approach that requires minimal financial and time commitments to facilitate the comprehensive analysis of locomotion in rodent disease models.

Corticospinal circuit remodeling after central nervous system injury is dependent on neuronal activity.

The remodeling of supraspinal axonal circuits mediates functional recovery after spinal cord injury. This process critically depends on the selection of appropriate synaptic connections between cortical projection and spinal relay neurons. To unravel the principles that guide this target selection, we used genetic and chemogenetic tools to modulate NMDA receptor (NMDAR) integrity and function, CREB-mediated transcription, and neuronal firing of relay neurons during injury-induced corticospinal remodeling. We show that NMDAR signaling and CREB-mediated transcription maintain nascent corticospinal tract (CST)-relay neuron contacts. These activity-dependent signals act during a defined period of circuit remodeling and do not affect mature or uninjured circuits. Furthermore, chemogenetic modulation of relay neuron activity reveals that the regrowing CST axons select their postsynaptic partners in a competitive manner and that preventing such activity-dependent shaping of corticospinal circuits limits motor recovery after spinal cord injury.

Combining molecular intervention with in vivo imaging to untangle mechanisms of axon pathology and outgrowth following spinal cord injury.

In vivo imaging of the spinal cord has allowed the observation of single axons over relatively long periods in the living mouse. After spinal cord injury, this methodology has helped to differentiate several pathological stages and tissue processes which impact axon morphology. In addition, the combination of in vivo imaging techniques with particular molecular intervention has shown that specific pathological axon changes can respond to distinct treatments. Combining in vivo imaging with molecular interventions is, hence, a powerful approach to extend our knowledge of the pathological processes leading to axonal loss. It also allows testing possible treatment options to, for example, increase axonal outgrowth. This review will provide a detailed description and critical examination of several studies that have combined the two methodologies in spinal cord injury research and pinpoints the specificities of the approach.