Reversible Disruption of Neuronal Mitochondria by Ischemic and Traumatic Injury Revealed by Quantitative Two-Photon Imaging in the Neocortex of Anesthetized Mice

Abstract

Mitochondria play a variety of functional roles in cortical neurons, from metabolic support and neuroprotection to the release of cytokines that trigger apoptosis. In dendrites, mitochondrial structure is closely linked to their function, and fragmentation (fission) of the normally elongated mitochondria indicates loss of their function under pathological conditions, such as stroke and brain trauma. Using in vivo two-photon microscopy in mouse brain, we quantified mitochondrial fragmentation in a full spectrum of cortical injuries, ranging from severe to mild. Severe global ischemic injury was induced by bilateral common carotid artery occlusion, whereas severe focal stroke injury was induced by Rose Bengal photosensitization. The moderate and mild traumatic injury was inflicted by focal laser lesion and by mild photo-damage, respectively. Dendritic and mitochondrial structural changes were tracked longitudinally using transgenic mice expressing fluorescent proteins localized either in cytosol or in mitochondrial matrix. In response to severe injury, mitochondrial fragmentation developed in parallel with dendritic damage signified by dendritic beading. Reconstruction from serial section electron microscopy confirmed mitochondrial fragmentation. Unlike dendritic beading, fragmentation spread beyond the injury core in focal stroke and focal laser lesion models. In moderate and mild injury, mitochondrial fragmentation was reversible with full recovery of structural integrity after 1-2 weeks. The transient fragmentation observed in the mild photo-damage model was associated with changes in dendritic spine density without any signs of dendritic damage. Our findings indicate that alterations in neuronal mitochondria structure are very sensitive to the tissue damage and can be reversible in ischemic and traumatic injuries.

Mitochondrial MPTP: A Novel Target of Ethnomedicine for Stroke Treatment by Apoptosis Inhibition

“…be a robust alternative for probing drug targeted regulation of MPTP. Moreover, patch-clamp combined with two-photon living cell imaging technology also had potential prospects for detection of prophylaxis and treatment of ethnic drugs on post-stroke mitochondrial MMP and Ca 2+ or other ion levels (Kislin et al, 2017;Wilson et al, 2018;Zhang et al, 2019c). In conclusion, we were optimistic that abnormal opening of mitochondrial MPTPinduced apoptosis would become a potential target for stroke treatment by ethnic medicine.…”

Mitochondrial Aspects of Neuronal Pathology in Triple-Transgenic Alzheimer’s Disease Mice

“…Also, fixation at room temperature, as was performed in this study, has been shown to reduce mitochondrial length in cultured cells compared to fixation at 37 o C [110]. It is possible to image mitochondria in the cortex of live, anesthetized mito-CFP mice through a cranial window [124], so future studies might be able to elucidate the differences in mitochondrial structure and number in live neurons versus fixed tissue to avoid these issues.…”

Phosphoregulation of DRP1 at the mitochondria in vivo regulates ischemic sensitivity in the brain and memory

“…Mitochondrial fission occurs in neurons during ischemic injury in vitro and in vivo and has been suggested to contribute to ischemic damage (Barsoum, Yuan et al 2006, Niizuma, Yoshioka et al 2010, Grohm, Kim et al 2012, Kumari, Mehta et al 2012, Li, Wang et al 2015, Sanderson, Raghunayakula et al 2015, Kislin, Sword et al 2017. The relationship between mitochondrial fission and ischemic injury appears more than correlative as inhibition of Drp1 with the small molecule inhibitor mdivi-1 was shown by several groups to decrease infarct volume following MCAO (Grohm, Kim et al 2012, Zhang, Wang et al 2013).…”

“…In addition to its ability to promote apoptosis, Bβ2/PP2A translocation to mitochondria also initiates mitochondrial fission (Dagda, Merrill et al 2008. Mitochondrial fission occurs in neurons during cerebral ischemia and has been suggested to contribute to ischemic damage (Barsoum, Yuan et al 2006, Grohm, Kim et al 2012, Li, Wang et al 2015, Kislin, Sword et al 2017. Given the decreased cerebral infarct volume observed in Bβ2 -/-mice and previous in vitro work suggesting Bβ2 promotes mitochondrial fission we were curious whether mitochondrial fission was inhibited in Bβ2 -/-mice.…”

“…decreases infarct volume following cerebral ischemia (Grohm, Kim et al 2012, Zhang, Wang et al 2013 here we illustrate inhibition of Drp1 through increased phosphorylation of Drp1-S656, as a result of Bβ2 deletion, is sufficient to reduce infarct volume following MCAO. Presumably inhibiting Drp1 prior to ischemic injury decreases infarct volume through preventing mitochondrial fission associated with ischemic insult (Barsoum, Yuan et al 2006, Kislin, Sword et al 2017. However, Drp1 inhibition in vitro does not prevent mitochondrial fission associated with glutamate excitotoxicity (Young, Pinon et al 2010.…”