Repair of traumatic plasmalemmal damage to neurons and other eukaryotic cells

The repair（sealing） of plasmalemmal damage,consisting of small holes to complete transections,is critical for cell survival,especially for neurons that rarely regenerate cell bodies.We first describe and evaluate different measures of cell sealing.Some measures,including morphological/ultra-structural observations,membrane potential,and input resistance,provide very ambiguous assessments of plasmalemmal sealing.In contrast,measures of ionic current flow and dye barriers can,if appropriately used,provide more accurate assessments.We describe the effects of various substances（calcium,calpains,cytoskeletal proteins,ESCRT proteins,m UNC-13,NSF,PEG） and biochemical pathways（PKA,PKC,PLC,Epac,cytosolic oxidation） on plasmalemmal sealing probability,and suggest that substances,pathways,and cellular events associated with plasmalemmal sealing have undergone a very conservative evolution.During sealing,calcium ion influx mobilizes vesicles and other membranous structures（lysosomes,mitochondria,etc.） in a continuous fashion to form a vesicular plug that gradually restricts diffusion of increasingly smaller molecules and ions over a period of seconds to minutes.Furthermore,we find no direct evidence that sealing occurs through the collapse and fusion of severed plasmalemmal leaflets,or in a single step involving the fusion of one large wound vesicle with the nearby,undamaged plasmalemma.We describe how increases in perikaryal calcium levels following axonal transection account for observations that cell body survival decreases the closer an axon is transected to the perikaryon.Finally,we speculate on relationships between plasmalemmal sealing,Wallerian degeneration,and the ability of polyethylene glycol（PEG） to seal cell membranes and rejoin severed axonal ends – an important consideration for the future treatment of trauma to peripheral nerves.A better knowledge of biochemical pathways and cytoplasmic structures involved in plasmalemmal sealing might provide insights to develop treatments for traumatic nerve injuries,stroke,muscular dystrophy,and other pathologies.

Elevated axonal membrane permeability and its correlation with motor deficits in an animal model of multiple sclerosis

Background:It is increasingly clear that in addition to myelin disruption,axonal degeneration may also represent a key pathology in multiple sclerosis(MS).Hence,elucidating the mechanisms of axonal degeneration may not only enhance our understanding of the overall MS pathology,but also elucidate additional therapeutic targets.The objective of this study is assess the degree of axonal membrane disruption and its significance in motor deficits in EAE mice.Methods:Experimental Autoimmune Encephalomyelitis was induced in mice by subcutaneous injection of myelin oligodendrocyte glycoprotein/complete Freud’s adjuvant emulsion,followed by two intraperitoneal injections of pertussis toxin.Behavioral assessment was performed using a 5-point scale.Horseradish Peroxidase Exclusion test was used to quantify the disruption of axonal membrane.Polyethylene glycol was prepared as a 30%(w/v)solution in phosphate buffered saline and injected intraperitoneally.Results:We have found evidence of axonal membrane disruption in EAE mice when symptoms peak and to a lesser degree,in the pre-symptomatic stage of EAE mice.Furthermore,polyethylene glycol(PEG),a known membrane fusogen,significantly reduces axonal membrane disruption in EAE mice.Such PEG-mediated membrane repair was accompanied by significant amelioration of behavioral deficits,including a delay in the emergence of motor deficits,a delay of the emergence of peak symptom,and a reduction in the severity of peak symptom.Conclusions:The current study is the first indication that axonal membrane disruption may be an important part of the pathology in EAE mice and may underlies behavioral deficits.Our study also presents the initial observation that PEG may be a therapeutic agent that can repair axolemma,arrest axonal degeneration and reduce motor deficits in EAE mice.