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Published on: January 3, 2025
Mechanisms underlying cell death in ischemia-like damage to the rat spinal cord in vitro
E Bianchetti1, M Mladinic, A Nistri
1Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy.
Abstract:
New spinal cord injury (SCI) cases are frequently due to non-traumatic causes, including vascular disorders. To develop mechanism-based neuroprotective strategies for acute SCI requires full understanding of the early pathophysiological changes to prevent disability and paralysis. The aim of our study was to identify the molecular and cellular mechanisms of cell death triggered by a pathological medium (PM) mimicking ischemia in the rat spinal cord in vitro. We previously showed that extracellular Mg(2+) (1 mM) worsened PM-induced damage and inhibited locomotor function. The present study indicated that 1 h of PM+Mg(2+) application induced delayed pyknosis chiefly in the spinal white matter via overactivation of poly (ADP-ribose) polymerase 1 (PARP1), suggesting cell death mediated by the process of parthanatos that was largely suppressed by pharmacological block of PARP-1. Gray matter damage was less intense and concentrated in dorsal horn neurons and motoneurons that became immunoreactive for the mitochondrial apoptosis-inducing factor (the intracellular effector of parthanatos) translocated into the nucleus to induce chromatin condensation and DNA fragmentation. Immunoreactivity to TRPM ion channels believed to be involved in ischemic brain damage was also investigated. TRPM2 channel expression was enhanced 24 h later in dorsal horn and motoneurons, whereas TRPM7 channel expression concomitantly decreased. Conversely, TRPM7 expression was found earlier (3 h) in white matter cells, whereas TRPM2 remained undetectable. Simulating acute ischemic-like damage in vitro in the presence of Mg(2+) showed how, during the first 24 h, this divalent cation unveiled differential vulnerability of white matter cells and motoneurons, with distinct changes in their TRPM expression.
Insights
Extracellular Mg(2+) worsens spinal cord injury (SCI) by triggering delayed cell death via PARP1 activation. This study reveals distinct TRPM channel changes in white matter and neurons during early ischemic damage.
Area of Science:
- Neuroscience
- Cell Biology
- Pathophysiology
Background:
- Spinal cord injury (SCI) has significant non-traumatic causes, necessitating understanding of early molecular events for neuroprotection.
- Pathological mechanisms underlying acute SCI, particularly those involving ischemia, require detailed investigation to prevent paralysis.
Purpose of the Study:
- To elucidate the molecular and cellular mechanisms of cell death in rat spinal cord tissue exposed to an ischemia-mimicking pathological medium (PM) with extracellular Mg(2+).
- To investigate the role of poly (ADP-ribose) polymerase 1 (PARP1) and transient receptor potential melastatin (TRPM) ion channels in early SCI pathogenesis.
Main Methods:
- In vitro exposure of rat spinal cord tissue to a pathological medium (PM) with and without 1 mM extracellular Mg(2+).
- Assessment of cell death pathways, including parthanatos, via PARP1 activity and mitochondrial apoptosis-inducing factor (AIF) translocation.
- Evaluation of TRPM2 and TRPM7 ion channel expression using immunofluorescence at various time points (3h and 24h).
Main Results:
- PM with Mg(2+) induced delayed pyknosis in spinal white matter, mediated by PARP1 overactivation and suppressed by PARP-1 inhibition.
- Gray matter damage involved dorsal horn neurons and motoneurons exhibiting nuclear translocation of AIF, indicative of parthanatos.
- TRPM2 expression increased in gray matter (24h), while TRPM7 decreased; TRPM7 was detected earlier (3h) in white matter, with TRPM2 remaining undetectable.
Conclusions:
- Extracellular Mg(2+) exacerbates ischemic SCI by promoting parthanatos-dependent cell death in white matter and affecting neuronal apoptosis.
- Differential expression patterns of TRPM2 and TRPM7 channels highlight their distinct roles in the vulnerability of white matter and gray matter neurons during acute SCI.
- Understanding these early molecular events and ion channel dynamics is crucial for developing targeted neuroprotective strategies against SCI.
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