Selective vulnerability of motor neuron types and functional groups to degeneration in amyotrophic lateral sclerosis: review of the neurobiological mechanisms and functional correlates

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition characterised by a progressive loss of motor neurons controlling voluntary muscle activity. The disease manifests through a variety of motor dysfunctions related to the extent of damage and loss of neurons at different anatomical locations. Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared. In this article, we review the neurobiological mechanisms, neurochemical profiles, and morpho-functional characteristics of various motor neuron groups and types of motor units implicated in their differential exposure to degeneration. We discuss specific cell-autonomous (intrinsic) and extrinsic factors influencing the vulnerability gradient of motor units and motor neuron types to ALS, with their impact on disease manifestation, course, and prognosis, as revealed in preclinical and clinical studies. We consider the outstanding challenges and emerging opportunities for interpreting the phenotypic and mechanistic variability of the disease to identify targets for clinical interventions

Disruption of Myelin Leads to Ectopic Expression of K(V)1.1 Channels with Abnormal Conductivity of Optic Nerve Axons in a Cuprizone-Induced Model of Demyelination

The molecular determinants of abnormal propagation of action potentials along axons and ectopic conductance in demyelinating diseases of the central nervous system, like multiple sclerosis (MS),are poorly defined. Widespread interruption of myelin occurs in several mouse models of demyelination, rendering them useful for research. Herein, considerable myelin loss is shown in the optic nerves of cuprizone-treated demyelinating mice. Immuno-fluorescence confocal analysis of the expression and distribution of voltage-activated K+ channels (K(V)1.1 and 1.2 alpha subunits) revealed their spread from typical juxta-paranodal (JXP) sites to nodes in demyelinated axons, albeit with a disproportionate increase in the level of K(V)1.1 subunit. Functionally, in contrast to monophasic compound action potentials (CAPs) recorded in controls, responses derived from optic nerves of cuprizone-treated mice displayed initial synchronous waveform followed by a dispersed component. Partial restoration of CAPs by broad spectrum (4-aminopyridine) or K(V)1.1-subunit selective (dendrotoxin K) blockers of K+ currents suggest enhanced K(V)1.1-mediated conductance in the demyelinated optic nerve. Biophysical profiling of K+ currents mediated by recombinant channels comprised of different K(V)1.1 and 1.2 stoichiometries revealed that the enrichment of K(V)1 channels K(V)1.1 subunit endows a decrease in the voltage threshold and accelerates the activation kinetics. Together with the morphometric data, these findings provide important clues to a molecular basis for temporal dispersion of CAPs and reduced excitability of demyelinated optic nerves, which could be of potential relevance to the patho-physiology of MS and related disorders

Selective vulnerability of motor neuron types and functional groups to degeneration in amyotrophic lateral sclerosis: review of the neurobiological mechanisms and functional correlates

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition characterised by a progressive loss of motor neurons controlling voluntary muscle activity. The disease manifests through a variety of motor dysfunctions related to the extent of damage and loss of neurons at different anatomical locations. Despite extensive research, it remains unclear why some motor neurons are especially susceptible to the disease, while others are affected less or even spared. In this article, we review the neurobiological mechanisms, neurochemical profiles, and morpho-functional characteristics of various motor neuron groups and types of motor units implicated in their differential exposure to degeneration. We discuss specific cell-autonomous (intrinsic) and extrinsic factors influencing the vulnerability gradient of motor units and motor neuron types to ALS, with their impact on disease manifestation, course, and prognosis, as revealed in preclinical and clinical studies. We consider the outstanding challenges and emerging opportunities for interpreting the phenotypic and mechanistic variability of the disease to identify targets for clinical interventions.SVO: Innovation Fund Award 2022 from the University of Greenwich; VBO: Charles University, Third Faculty of Medicine Research Program COOPERATIO-207036; Medical Diagnostics and Basic Medical Sciences in ‘Medical Genetics’; SM: Generalitat Valenciana (GVA: Prometeo/2018/041); MINECO/AEI/ERDF, EU, Spanish State Research Agency, and the European Union via the European Regional Development Fund (ERDF)—“Una manera de hacer Europa” (SAF2017-83702-R); Instituto de Salud Carlos III (“RD16/001/0010”, co-funded by ERDF).Peer reviewe

The glucose-dependent insulinotropic polypeptide and glucose-stimulated insulin response to exercise training and diet in obesity

Aging and obesity are characterized by decreased β-cell sensitivity and defects in the potentiation of nutrient-stimulated insulin secretion by GIP. Exercise and diet are known to improve glucose metabolism and the pancreatic insulin response to glucose, and this effect may be mediated through the incretin effect of GIP. The purpose of this study was to assess the effects of a 12-wk exercise training intervention (5 days/wk, 60 min/day, 75% V̇o2 max) combined with a eucaloric (EX, n = 10) or hypocaloric (EX-HYPO, pre: 1,945 ± 190, post: 1,269 ± 70, kcal/day; n = 9) diet on the GIP response to glucose in older (66.8 ± 1.5 yr), obese (34.4 ± 1.7 kg/m2) adults with impaired glucose tolerance. In addition to GIP, plasma PYY3–36, insulin, and glucose responses were measured during a 3-h, 75-g oral glucose tolerance test. Both interventions led to a significant improvement in V̇o2 max (P < 0.05). Weight loss (kg) was significant in both groups but was greater after EX-HYPO (−8.3 ± 1.1 vs. −2.8 ± 0.5, P = 0.002). The glucose-stimulated insulin response was reduced after EX-HYPO (P = 0.02), as was the glucose-stimulated GIP response (P < 0.05). Furthermore, after the intervention, changes in insulin (ΔI0–30/ΔG0–30) and GIP (Δ0–30) secretion were correlated (r = 0.69, P = 0.05). The PYY3–36 (Δ0–30) response to glucose was increased after both interventions (P < 0.05). We conclude that 1) a combination of caloric restriction and exercise reduces the GIP response to ingested glucose, 2) GIP may mediate the attenuated glucose-stimulated insulin response after exercise/diet interventions, and 3) the increased PYY3–36 response represents an improved capacity to regulate satiety and potentially body weight in older, obese, insulin-resistant adults

Exercise and diet enhance fat oxidation and reduce insulin resistance in older obese adults

Older, obese, and sedentary individuals are at high risk of developing diabetes and cardiovascular disease. Exercise training improves metabolic anomalies associated with such diseases, but the effects of caloric restriction in addition to exercise in such a high risk group are not known. Changes in body composition and metabolism during a lifestyle intervention were investigated in twenty three older, obese men and women (aged 66 ± 1 years, BMI 33.2 ± 1.4 kg.m(−2)) with impaired glucose tolerance. All volunteers undertook twelve weeks of aerobic exercise training (5 days per week for 60 min @ 75% VO(2)max) with either normal caloric intake (eucaloric group, 1901 ± 277 kcal.day(−1), n = 12) or a reduced-calorie diet (hypocaloric group, 1307 ± 70 kcal.day(−1), n = 11), as dictated by nutritional counseling. Body composition (decreased fat mass; maintained fat-free mass), aerobic fitness (VO(2)max), leptinemia, insulin sensitivity, and intramyocellular lipid accumulation (IMCL) in skeletal muscle improved in both groups (P < 0.05). Improvements in body composition, leptin and basal fat oxidation were greater in the hypocaloric group. Following the intervention there was a correlation between the increase in basal fat oxidation and the decrease in IMCL (r = −0.53, P = 0.04). In addition, basal fat oxidation was associated with circulating leptin after (r = 0.65, P = 0.0007), but not before the intervention (r = 0.05, P = 0.84). In conclusion, these data show that exercise training improves resting substrate oxidation and creates a metabolic milieu that appears to promote lipid utilization in skeletal muscle, thus facilitating a reversal of insulin resistance. We also demonstrate that leptin sensitivity is improved, but that such a trend may rely on reducing caloric intake in addition to exercise training

Demyelination disrupts the conductivity of ON axons which can be partially restored by 4-AP.

<p>(A, B) A low magnification micrograph (4×) demonstrating the semi-dissected ON (ventral view) with stimulation (suction, Suc. pipette) and recording (Rec.) electrodes. Graded synchronous CAPs recorded from control animals contrasting with bi-component CAPs derived from experimental ON activated from elevated stimuli thresholds (<b>C</b>). Insert illustrates the experimental set-up for CAPs recordings. Rec. - recording electrode; Suc. - suction pipette used for stimulation. ON – optic nerve, OX – optic xiasm. (<b>B</b>) Typical CAPs evoked in control ON by paired-pulse stimulation (PPS). Note the second CAP from the refractory phase following the first CAP. The evoked CAPs recorded from cuprizone-treated (demyelinated) ON axons showed lower amplitudes and protracted late components compared to the untreated (myelinated) ON axons. (<b>C</b>) Stimulus-response relation of CAPs in controls and experimental ON, showing lower activation threshold and higher amplitudes of evoked CAPs in demyelianted ON. (<b>D</b>) Representative recordings of CAPs from ON of control and cuprizone fed mice before (1) in the presence of TEA (2, upper row) or 4-AP (lower row) and (1+2) superimposed traces. (F, G) Summary of the effects of TEA (15–20 min application) on the CAPs in control and cuprizone-treated ONs (n = 5 in each group) (<b>E</b>) The summary histogram of CAP amplitudes scored before and after application of 1 mM 4-AP. Note the significant enhancement of the CAP amplitudes in demyelinated ON caused by 4- AP (P<0.05, n = 5 in each group).</p

Functional characterization of recombinant K_V1.1 homo-tetramers reveals distinctive biophysical profiles from those of K_V1.1/1.2 heteromers.

<p>(<b>A</b>) Western blots of surface expressed concatenated K_V1 channels in[HEK293 cells. Lanes: 1, non-transfected cells show no immuno-reactivity for K_V1.1 (or K_V1.2, not shown); 2, K_V(1.1)₄ and 3, K_V1.1-1.1-1.2-1.1 detected with anti-K_V1.1 IgG giving a band size of ∼250 kD; 4 and 6, K_V(1.2)₄ homo-tetramer was non-reactive with anti-K_V1.1 IgG (4) but gave a distinct band when probed with K_V1.2 IgG (6). Protein markers are indicated in lanes 5 and 7. (<b>B, D1–F1</b>) Representative recordings of macroscopic currents (300 ms pulse) from HEK293 cells transfected with the individual recombinant channels. (<b>B, C</b>) Activation rate of the voltage-dependent K⁺ currents mediated by K_V(1.1)₄ (left) and K_V(1.2)₄ (middle) channels (within the range of 10–30% of max. current) at 5 mV from indicated voltages (below) with super-imposed (right) representative traces from. A notable difference between the rates of activation of K_V(1.1)₄ and K_V(1.2)₄ is revealed by fitting the data with a single exponential (see <b>C</b>). (<b>D2–F2</b>) Conductance-voltage relations of macroscopic currents measured, based on the K⁺ current of the last 100 ms for each channel. Conductance at various command potentials were normalised and fitted with a single Boltzmann function. The difference in conductance values of K_V(1.1)₄ and K_V(1.2)₄ channel were statistically significant from −55 mV (P<0.05, Mann-Whitney <i>U</i>-test, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087736#pone-0087736-t001" target="_blank">Table 1</a> for summary of the biophysical data).</p

Demyelination alters the distribution and composition of K_V1 channels in ON.

<p>Double [pan-Na (red)/K_V1.2 (green)] immuno-labelling of control (<b>A1</b>) and experimental (<b>A2</b>) ON: note elongated JXPs with alterations in most of the nodal Na_V channel clusters in samples from the cuprizone-treated mice. (<b>B1–2</b>) Double immuno-labelling of ON for K_V1.1 (red) and K_V1.2 (green) subunits of K_V1 channels: control (<b>B1</b>) and experimental (<b>B2</b>) samples, respectively. Note the highly localized occurrence of these proteins in JXPs of controls contrasting with their diffuse location along the ON axons in demyelinated specimens. Yellow staining corresponds to JXP regions showing co-localization of these proteins. The scale bars for low and high magnifications are 6 and 2 µm, respectively. (<b>C</b>) Summary histogram of the intact JXP labelled with anti-K_V1.2 antibody of control and experimental ON axons (n = 3 in each group). (<b>D</b>) A plot of the mean area of JXPs labelled for K_V1.1 channels in control (2.4±0.5 µm²) compared to the increased area of fluorescence intensity of JXPs in demyelinated (8.2±1 µm²) axons. (<b>E</b>) The mean fluorescence area of JXPs labelled for Kv1.2 channels in control (3.8±0.4) was lower than that in the treated ON axons (8.2±1 µm²). (<b>F</b>) A summary histogram of K_V1.1 and 1.2 co-localization in control (0.86±0.06) and demyelinated (0.27±0.04) ON demonstrating a significant (p<0.001) reduction in the degree of K_V1.1/1.2 co-localization in ON axons of the experimental mice. (<b>G</b>) The degree of K_V1.2/1.1 co-localization in ON axons of the experimental mice showed a reduction, which is still significant (P<0.05), when comparing the control (0.71±0.06) and the demyelinated ON (0.49±0.04) values. Data are taken from control and demylinated ON axons of 3 animals, in each group.</p