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Two different pathogenic mechanisms, dying-back axonal neuropathy and pancreatic senescence, are present in the YG8R mouse model of Friedreich ’ s ataxia

View Article: PubMed Central - PubMed

ABSTRACT

Frataxin (FXN) deficiency causes Friedreich’s ataxia (FRDA), a multisystem disorder with neurological and non-neurological symptoms. FRDA pathophysiology combines developmental and degenerative processes of dorsal root ganglia (DRG), sensory nerves, dorsal columns and other central nervous structures. A dying-back mechanism has been proposed to explain the peripheral neuropathy and neuropathology. In addition, affected individuals have non-neuronal symptoms such as diabetes mellitus or glucose intolerance. To go further in the understanding of the pathogenic mechanisms of neuropathy and diabetes associated with the disease, we have investigated the humanized mouse YG8R model of FRDA. By biochemical and histopathological studies, we observed abnormal changes involving muscle spindles, dorsal root axons and DRG neurons, but normal findings in the posterior columns and brain, which agree with the existence of a dying-back process similar to that described in individuals with FRDA. In YG8R mice, we observed a large number of degenerated axons surrounded by a sheath exhibiting enlarged adaxonal compartments or by a thin disrupted myelin sheath. Thus, both axonal damage and defects in Schwann cells might underlie the nerve pathology. In the pancreas, we found a high proportion of senescent islets of Langerhans in YG8R mice, which decreases the β-cell number and islet mass to pathological levels, being unable to maintain normoglycemia. As a whole, these results confirm that the lack of FXN induces different pathogenic mechanisms in the nervous system and pancreas in the mouse model of FRDA: dying back of the sensory nerves, and pancreatic senescence.

No MeSH data available.


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Assessment of mitochondrial bioenergetics in neuronal tissues (brainstem, posterior columns, nerve roots and dorsal root ganglia). A quantitative western blot assay was developed to measure FXN (A), COXI and COXII (B), cytochrome c (C), ATP synthase (D) and TOM22 (E) in neuronal tissues [brainstem, posterior columns (PC), nerve roots and dorsal root ganglia (DRG)]. (A) Representative western blot of human FXN expression in YG8R mice in the four neuronal tissues used in the study. Human FXN was only detected in YG8R mice, in which the transgene was present, and not in wild type (WT; data not shown). Western blot results were quantified for each lane using Fujifilm's Multi-Gauge software. To allow for loading variation, values were normalized to the actin control. Final values were expressed as a ratio to the value of FXN expression in nerve roots. DRG and nerve roots (distal tissues) expressed less FXN than the posterior columns and brainstem (proximal tissues). Values are expressed as mean±s.e.m.; ***P<0.001 neuronal tissues of YG8R (DRG/PC/brainstem) compared with YG8R roots. (B-E) Western blot results were quantified as in A, but the final values were expressed as a percentage of the C57BL/6J value. The most affected tissues were the distal tissues, especially the nerve roots. (E) Graph of TOM22 confirmed that the differences observed in the previous studies were not due to a reduction in mitochondrial number. Values are expressed as mean±s.e.m.; **P≤0.01 YG8R compared with WT (C57).
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DMM024273F2: Assessment of mitochondrial bioenergetics in neuronal tissues (brainstem, posterior columns, nerve roots and dorsal root ganglia). A quantitative western blot assay was developed to measure FXN (A), COXI and COXII (B), cytochrome c (C), ATP synthase (D) and TOM22 (E) in neuronal tissues [brainstem, posterior columns (PC), nerve roots and dorsal root ganglia (DRG)]. (A) Representative western blot of human FXN expression in YG8R mice in the four neuronal tissues used in the study. Human FXN was only detected in YG8R mice, in which the transgene was present, and not in wild type (WT; data not shown). Western blot results were quantified for each lane using Fujifilm's Multi-Gauge software. To allow for loading variation, values were normalized to the actin control. Final values were expressed as a ratio to the value of FXN expression in nerve roots. DRG and nerve roots (distal tissues) expressed less FXN than the posterior columns and brainstem (proximal tissues). Values are expressed as mean±s.e.m.; ***P<0.001 neuronal tissues of YG8R (DRG/PC/brainstem) compared with YG8R roots. (B-E) Western blot results were quantified as in A, but the final values were expressed as a percentage of the C57BL/6J value. The most affected tissues were the distal tissues, especially the nerve roots. (E) Graph of TOM22 confirmed that the differences observed in the previous studies were not due to a reduction in mitochondrial number. Values are expressed as mean±s.e.m.; **P≤0.01 YG8R compared with WT (C57).

Mentions: To determine the major neural structural level responsible for motor coordination dysfunction in the spinal cord, we proceeded to investigate molecular changes by western blot analysis in the YG8R mouse. We selected the DRGs, nerve roots, posterior columns of the spinal cord, and brainstem because they are affected in the neuropathology of FRDA. Studies were carried out on 19- to 22-month-old mice, the age at which motor coordination abnormalities had been observed. First, we analyzed FXN and proteins involved in biological processes related to neurodegeneration. FXN levels were reduced in nerve roots and DRGs (Fig. 2A). In contrast, levels in the brainstem were 18-fold higher than in the nerve roots. This finding suggests that a reduction of FXN levels is more evident in peripheral (nerve roots and DRG) than central (posterior columns and brainstem) neural structures.Fig. 2.


Two different pathogenic mechanisms, dying-back axonal neuropathy and pancreatic senescence, are present in the YG8R mouse model of Friedreich ’ s ataxia
Assessment of mitochondrial bioenergetics in neuronal tissues (brainstem, posterior columns, nerve roots and dorsal root ganglia). A quantitative western blot assay was developed to measure FXN (A), COXI and COXII (B), cytochrome c (C), ATP synthase (D) and TOM22 (E) in neuronal tissues [brainstem, posterior columns (PC), nerve roots and dorsal root ganglia (DRG)]. (A) Representative western blot of human FXN expression in YG8R mice in the four neuronal tissues used in the study. Human FXN was only detected in YG8R mice, in which the transgene was present, and not in wild type (WT; data not shown). Western blot results were quantified for each lane using Fujifilm's Multi-Gauge software. To allow for loading variation, values were normalized to the actin control. Final values were expressed as a ratio to the value of FXN expression in nerve roots. DRG and nerve roots (distal tissues) expressed less FXN than the posterior columns and brainstem (proximal tissues). Values are expressed as mean±s.e.m.; ***P<0.001 neuronal tissues of YG8R (DRG/PC/brainstem) compared with YG8R roots. (B-E) Western blot results were quantified as in A, but the final values were expressed as a percentage of the C57BL/6J value. The most affected tissues were the distal tissues, especially the nerve roots. (E) Graph of TOM22 confirmed that the differences observed in the previous studies were not due to a reduction in mitochondrial number. Values are expressed as mean±s.e.m.; **P≤0.01 YG8R compared with WT (C57).
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4920149&req=5

DMM024273F2: Assessment of mitochondrial bioenergetics in neuronal tissues (brainstem, posterior columns, nerve roots and dorsal root ganglia). A quantitative western blot assay was developed to measure FXN (A), COXI and COXII (B), cytochrome c (C), ATP synthase (D) and TOM22 (E) in neuronal tissues [brainstem, posterior columns (PC), nerve roots and dorsal root ganglia (DRG)]. (A) Representative western blot of human FXN expression in YG8R mice in the four neuronal tissues used in the study. Human FXN was only detected in YG8R mice, in which the transgene was present, and not in wild type (WT; data not shown). Western blot results were quantified for each lane using Fujifilm's Multi-Gauge software. To allow for loading variation, values were normalized to the actin control. Final values were expressed as a ratio to the value of FXN expression in nerve roots. DRG and nerve roots (distal tissues) expressed less FXN than the posterior columns and brainstem (proximal tissues). Values are expressed as mean±s.e.m.; ***P<0.001 neuronal tissues of YG8R (DRG/PC/brainstem) compared with YG8R roots. (B-E) Western blot results were quantified as in A, but the final values were expressed as a percentage of the C57BL/6J value. The most affected tissues were the distal tissues, especially the nerve roots. (E) Graph of TOM22 confirmed that the differences observed in the previous studies were not due to a reduction in mitochondrial number. Values are expressed as mean±s.e.m.; **P≤0.01 YG8R compared with WT (C57).
Mentions: To determine the major neural structural level responsible for motor coordination dysfunction in the spinal cord, we proceeded to investigate molecular changes by western blot analysis in the YG8R mouse. We selected the DRGs, nerve roots, posterior columns of the spinal cord, and brainstem because they are affected in the neuropathology of FRDA. Studies were carried out on 19- to 22-month-old mice, the age at which motor coordination abnormalities had been observed. First, we analyzed FXN and proteins involved in biological processes related to neurodegeneration. FXN levels were reduced in nerve roots and DRGs (Fig. 2A). In contrast, levels in the brainstem were 18-fold higher than in the nerve roots. This finding suggests that a reduction of FXN levels is more evident in peripheral (nerve roots and DRG) than central (posterior columns and brainstem) neural structures.Fig. 2.

View Article: PubMed Central - PubMed

ABSTRACT

Frataxin (FXN) deficiency causes Friedreich&rsquo;s ataxia (FRDA), a multisystem disorder with neurological and non-neurological symptoms. FRDA pathophysiology combines developmental and degenerative processes of dorsal root ganglia (DRG), sensory nerves, dorsal columns and other central nervous structures. A dying-back mechanism has been proposed to explain the peripheral neuropathy and neuropathology. In addition, affected individuals have non-neuronal symptoms such as diabetes mellitus or glucose intolerance. To go further in the understanding of the pathogenic mechanisms of neuropathy and diabetes associated with the disease, we have investigated the humanized mouse YG8R model of FRDA. By biochemical and histopathological studies, we observed abnormal changes involving muscle spindles, dorsal root axons and DRG neurons, but normal findings in the posterior columns and brain, which agree with the existence of a dying-back process similar to that described in individuals with FRDA. In YG8R mice, we observed a large number of degenerated axons surrounded by a sheath exhibiting enlarged adaxonal compartments or by a thin disrupted myelin sheath. Thus, both axonal damage and defects in Schwann cells might underlie the nerve pathology. In the pancreas, we found a high proportion of senescent islets of Langerhans in YG8R mice, which decreases the &beta;-cell number and islet mass to pathological levels, being unable to maintain normoglycemia. As a whole, these results confirm that the lack of FXN induces different pathogenic mechanisms in the nervous system and pancreas in the mouse model of FRDA: dying back of the sensory nerves, and pancreatic senescence.

No MeSH data available.


Related in: MedlinePlus