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RIP2-mediated LKB1 deletion causes axon degeneration in the spinal cord and hind-limb paralysis.

Sun G, Reynolds R, Leclerc I, Rutter GA - Dis Model Mech (2010)

Bottom Line: The molecular basis of this process remains largely unknown.Microtubule structures were also affected in the degenerated foci, with diminished neurofilament and tubulin expression.Deletion of both PRKAA1 genes, whose products AMPKα1 and AMPKα2 are also downstream targets of LKB1, with the same strategy was without effect.

View Article: PubMed Central - PubMed

Affiliation: Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, UK.

ABSTRACT
Axon degeneration is observed in neurodegenerative diseases and neuroinflammatory disorders, such as Alzheimer's disease, Parkinson's disease and multiple sclerosis. The molecular basis of this process remains largely unknown. Here, we show that mice deleted for the tumour suppressor LKB1 (also called STK11) in the spinal cord, some parts of the brain and in the endocrine pancreas (βLKB1KO mice) develop hind-limb dysfunction and axon degeneration at about 7 weeks. Demyelination and macrophage infiltration are observed in the white matter of these mice, predominantly in the bilateral and anterior funiculi of the thoracic segment of the spinal cord, suggesting damage to the ascending sensory signalling pathway owing to LKB1 deletion in the brain. Microtubule structures were also affected in the degenerated foci, with diminished neurofilament and tubulin expression. Deletion of both PRKAA1 genes, whose products AMPKα1 and AMPKα2 are also downstream targets of LKB1, with the same strategy was without effect. We thus define LKB1 as an intrinsic suppressor of axon degeneration and a possible target for strategies that can reverse this process.

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Related in: MedlinePlus

Histological changes in white matter in the thoracic region of spinal cord of βLKB1KO mice. (A) Representative H&E staining (a–e) and LFB staining (f–j) of the white matter of the thoracic region of spinal cord from wild-type mice (a,f) and βLKB1KO mice before (b,g), or 1 day (c,h) or 7 days (d,i) after the initial onset of hind-limb dysfunction, or of the less-affected white matter of the thoracic region of spinal cord from βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction (e,j). Arrows indicate eosinophilic spheroid. Scale bar: 50 μm. (B) Representative H&E staining (a–d) and LFB staining (e–h) of transverse sections of the thoracic region of spinal cord from wild-type mice (a,b,e,f) and βLKB1KO mice 1 day after initial onset of hind-limb dysfunction (c,d,g,h). Arrows indicate eosinophilic spheroid. Scale bars: 100 μm (a,c,e,g); 50 μm (b,d,f,h). (C,D) Quantification of degenerating (C) and demyelinated (D) axons in thoracic, cervical and lumbar regions of white matter spinal cord from βLKB1KO mice before or after 1 day and 7 days of initial onset of hind-limb dysfunction, and their wild-type controls. Intensity of axon staining per μm2 area of white matter were measured based on NF165kD (C) and LFB staining (D) using ImageJ. *P<0.05, **P<0.01, ***P<0.001. n=4 mice per genotype.
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f2-0040193: Histological changes in white matter in the thoracic region of spinal cord of βLKB1KO mice. (A) Representative H&E staining (a–e) and LFB staining (f–j) of the white matter of the thoracic region of spinal cord from wild-type mice (a,f) and βLKB1KO mice before (b,g), or 1 day (c,h) or 7 days (d,i) after the initial onset of hind-limb dysfunction, or of the less-affected white matter of the thoracic region of spinal cord from βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction (e,j). Arrows indicate eosinophilic spheroid. Scale bar: 50 μm. (B) Representative H&E staining (a–d) and LFB staining (e–h) of transverse sections of the thoracic region of spinal cord from wild-type mice (a,b,e,f) and βLKB1KO mice 1 day after initial onset of hind-limb dysfunction (c,d,g,h). Arrows indicate eosinophilic spheroid. Scale bars: 100 μm (a,c,e,g); 50 μm (b,d,f,h). (C,D) Quantification of degenerating (C) and demyelinated (D) axons in thoracic, cervical and lumbar regions of white matter spinal cord from βLKB1KO mice before or after 1 day and 7 days of initial onset of hind-limb dysfunction, and their wild-type controls. Intensity of axon staining per μm2 area of white matter were measured based on NF165kD (C) and LFB staining (D) using ImageJ. *P<0.05, **P<0.01, ***P<0.001. n=4 mice per genotype.

Mentions: To try to understand the molecular and cellular basis of the above changes, post-mortem analysis of different organs extracted from βLKB1KO mice was performed 1 or 7 days after the initial onset of hind-limb dysfunction. The tissues analyzed included: whole brain (cerebral cortex, hypothalamus and cerebellum), heart, lung, liver, spleen, kidney, skeletal muscle of hind limb, pelvis, sciatic nerve and spinal cord. Haematoxylin and eosin (H&E) staining was used for general morphological analysis and luxol fast blue (LFB) was used to detect myelin. This analysis revealed several large foci of axon degeneration in the white matter of the thoracic region of βLKB1KO mouse spinal cord 7 days after the initial onset of hind-limb disability (Fig. 2Ad,Ai), whereas fewer and smaller foci only were found 1 day after initial onset (Fig. 2Ac,Ah). In the area where degeneration occurred, axon disintegration and demyelination were evident by using LFB staining, with a loss of dark blue myelin staining and the formation of large digestion chambers caused by myelin vacuolation (Fig. 2Af,Ah,Ai,Bb,Bd,Bf,Bh). Notably, brightly eosinophilic acellular spheroids were present in some of the vacuolated chambers when the sections were stained with H&E (Fig. 2Ac,Bd, arrows), suggesting possible necrosis or swollen axons (Fig. 2Bd,Bh) (Fujimura et al., 2009). At 7 days after the onset of hind-limb dysfunction in βLKB1KO mice, a complete loss of myelin staining and the disappearance of axons was observed in the thoracic region of the spinal cord (Fig. 2Ad,Ai,C,D). A striking increase in the overall number of cell nuclei was also evident at the foci of degeneration of βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction, which is suggestive of inflammation and macrophage infiltration, and this increase continued as degeneration progressed (Fig. 2Ac,Ad,Ah,Ai and Fig. 4A). In addition to the large foci of axon degeneration, several smaller foci with fewer and smaller digestion chambers and vacuolated axons were found in the thoracic area of the spinal cord (Fig. 2Ae,Aj). In these areas, axons were not completely disintegrated, but still retained a partial myelin sheath, which was detached from the axons.


RIP2-mediated LKB1 deletion causes axon degeneration in the spinal cord and hind-limb paralysis.

Sun G, Reynolds R, Leclerc I, Rutter GA - Dis Model Mech (2010)

Histological changes in white matter in the thoracic region of spinal cord of βLKB1KO mice. (A) Representative H&E staining (a–e) and LFB staining (f–j) of the white matter of the thoracic region of spinal cord from wild-type mice (a,f) and βLKB1KO mice before (b,g), or 1 day (c,h) or 7 days (d,i) after the initial onset of hind-limb dysfunction, or of the less-affected white matter of the thoracic region of spinal cord from βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction (e,j). Arrows indicate eosinophilic spheroid. Scale bar: 50 μm. (B) Representative H&E staining (a–d) and LFB staining (e–h) of transverse sections of the thoracic region of spinal cord from wild-type mice (a,b,e,f) and βLKB1KO mice 1 day after initial onset of hind-limb dysfunction (c,d,g,h). Arrows indicate eosinophilic spheroid. Scale bars: 100 μm (a,c,e,g); 50 μm (b,d,f,h). (C,D) Quantification of degenerating (C) and demyelinated (D) axons in thoracic, cervical and lumbar regions of white matter spinal cord from βLKB1KO mice before or after 1 day and 7 days of initial onset of hind-limb dysfunction, and their wild-type controls. Intensity of axon staining per μm2 area of white matter were measured based on NF165kD (C) and LFB staining (D) using ImageJ. *P<0.05, **P<0.01, ***P<0.001. n=4 mice per genotype.
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Related In: Results  -  Collection

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f2-0040193: Histological changes in white matter in the thoracic region of spinal cord of βLKB1KO mice. (A) Representative H&E staining (a–e) and LFB staining (f–j) of the white matter of the thoracic region of spinal cord from wild-type mice (a,f) and βLKB1KO mice before (b,g), or 1 day (c,h) or 7 days (d,i) after the initial onset of hind-limb dysfunction, or of the less-affected white matter of the thoracic region of spinal cord from βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction (e,j). Arrows indicate eosinophilic spheroid. Scale bar: 50 μm. (B) Representative H&E staining (a–d) and LFB staining (e–h) of transverse sections of the thoracic region of spinal cord from wild-type mice (a,b,e,f) and βLKB1KO mice 1 day after initial onset of hind-limb dysfunction (c,d,g,h). Arrows indicate eosinophilic spheroid. Scale bars: 100 μm (a,c,e,g); 50 μm (b,d,f,h). (C,D) Quantification of degenerating (C) and demyelinated (D) axons in thoracic, cervical and lumbar regions of white matter spinal cord from βLKB1KO mice before or after 1 day and 7 days of initial onset of hind-limb dysfunction, and their wild-type controls. Intensity of axon staining per μm2 area of white matter were measured based on NF165kD (C) and LFB staining (D) using ImageJ. *P<0.05, **P<0.01, ***P<0.001. n=4 mice per genotype.
Mentions: To try to understand the molecular and cellular basis of the above changes, post-mortem analysis of different organs extracted from βLKB1KO mice was performed 1 or 7 days after the initial onset of hind-limb dysfunction. The tissues analyzed included: whole brain (cerebral cortex, hypothalamus and cerebellum), heart, lung, liver, spleen, kidney, skeletal muscle of hind limb, pelvis, sciatic nerve and spinal cord. Haematoxylin and eosin (H&E) staining was used for general morphological analysis and luxol fast blue (LFB) was used to detect myelin. This analysis revealed several large foci of axon degeneration in the white matter of the thoracic region of βLKB1KO mouse spinal cord 7 days after the initial onset of hind-limb disability (Fig. 2Ad,Ai), whereas fewer and smaller foci only were found 1 day after initial onset (Fig. 2Ac,Ah). In the area where degeneration occurred, axon disintegration and demyelination were evident by using LFB staining, with a loss of dark blue myelin staining and the formation of large digestion chambers caused by myelin vacuolation (Fig. 2Af,Ah,Ai,Bb,Bd,Bf,Bh). Notably, brightly eosinophilic acellular spheroids were present in some of the vacuolated chambers when the sections were stained with H&E (Fig. 2Ac,Bd, arrows), suggesting possible necrosis or swollen axons (Fig. 2Bd,Bh) (Fujimura et al., 2009). At 7 days after the onset of hind-limb dysfunction in βLKB1KO mice, a complete loss of myelin staining and the disappearance of axons was observed in the thoracic region of the spinal cord (Fig. 2Ad,Ai,C,D). A striking increase in the overall number of cell nuclei was also evident at the foci of degeneration of βLKB1KO mice 1 day after the initial onset of hind-limb dysfunction, which is suggestive of inflammation and macrophage infiltration, and this increase continued as degeneration progressed (Fig. 2Ac,Ad,Ah,Ai and Fig. 4A). In addition to the large foci of axon degeneration, several smaller foci with fewer and smaller digestion chambers and vacuolated axons were found in the thoracic area of the spinal cord (Fig. 2Ae,Aj). In these areas, axons were not completely disintegrated, but still retained a partial myelin sheath, which was detached from the axons.

Bottom Line: The molecular basis of this process remains largely unknown.Microtubule structures were also affected in the degenerated foci, with diminished neurofilament and tubulin expression.Deletion of both PRKAA1 genes, whose products AMPKα1 and AMPKα2 are also downstream targets of LKB1, with the same strategy was without effect.

View Article: PubMed Central - PubMed

Affiliation: Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial College London, London, UK.

ABSTRACT
Axon degeneration is observed in neurodegenerative diseases and neuroinflammatory disorders, such as Alzheimer's disease, Parkinson's disease and multiple sclerosis. The molecular basis of this process remains largely unknown. Here, we show that mice deleted for the tumour suppressor LKB1 (also called STK11) in the spinal cord, some parts of the brain and in the endocrine pancreas (βLKB1KO mice) develop hind-limb dysfunction and axon degeneration at about 7 weeks. Demyelination and macrophage infiltration are observed in the white matter of these mice, predominantly in the bilateral and anterior funiculi of the thoracic segment of the spinal cord, suggesting damage to the ascending sensory signalling pathway owing to LKB1 deletion in the brain. Microtubule structures were also affected in the degenerated foci, with diminished neurofilament and tubulin expression. Deletion of both PRKAA1 genes, whose products AMPKα1 and AMPKα2 are also downstream targets of LKB1, with the same strategy was without effect. We thus define LKB1 as an intrinsic suppressor of axon degeneration and a possible target for strategies that can reverse this process.

Show MeSH
Related in: MedlinePlus