Roman Del Arco Paloma

GDAP1 is an outer mitochondrial membrane protein affiliated in Charcot-Marie-Tooth (CMT) disease. Absence of GDAP1 gives rise to transformed mitochondrial networks and endoplasmic delusion (ER)-mitochondrial interactions result in ns decreased ER-Ca2+ levels follow me with ns defect top top store-operated calcium entry (SOCE) associated to a misallocation that mitochondria to subplasmalemmal sites. Ns defect top top SOCE is mimicked by MCU silencing or mitochondrial depolarization, which prevent mitochondrial calcium uptake. Ca2+ relax from después ER y Ca2+ inflow v SOCE in neuroblastoma cells result in un Ca2+-dependent upregulation the respiration i m sorry is blunted in GDAP1 silenced cells. Lessened SOCE in cells con CMT recessive missense mutations in los α-loop the GDAP1, however not leading mutations, was associated with smaller SOCE-stimulated respiration. These situations of GDAP1 deficiency additionally resulted in uno decreased ER-Ca2+ level which may have actually pathological implications. Los results indicate that CMT neurons may be under energetic constraints upon stimulation through Ca2+ mobilization agonists and point to un potential function of perturbed mitochondria-ER communication related to power metabolism in creates of CMT brought about by part of los recessive or null mutations of GDAP1.

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Charcot-Marie-Tooth (CMT) an illness is los most typical inherited neuromuscular disorder defined by grande locus heterogeneity1,2. Mutations in los GDAP1 gene show phenotypic y Mendelian heterogeneity in CMT patients and lead to several develops of CMT consisting of recessive demyelinating (CMT4A)3, recessive axonal (AR-CMT2K)4, recessive con intermediate clinical functions (CMTRIA)5 y a dominant inheritance pattern y axonal functions (CMT2K)6,7.

GDAP1 is an outer mitochondrial membrane protein include glutathione-S-transferase escribe domains8, y it has been regarded mitochondrial fission/fusion9,10,11,12 or oxidation processes13,14. On ns other hand, GDAP1 interacts with caytaxin and RAB6B, involved in anterograde-retrograde movement of vesicles15. Offered the strategic localization of GDAP1 in los outer mitochondrial membrane, y the number of interacting partner of los protein, the is meant that mutations in the protein can provide rise to countless nonexclusive results on cell function, and understanding i beg your pardon of castle is eventually responsible for ns disease phenotype is a de verdad challenge.

GDAP1-knockdown (KD) in the humanidad neuroblastoma SH-SY5Y cells outcomes in ns defect in store-operated calcium entry (SOCE)15, a calcium entrance pathway activated delaware discharge of ER-Ca2+ stores16. SOCE is regulated by mitochondria in different cell types17,18,19,20, and Ca2+ uptake by mitochondria through mitochondrial calcium uniporter (MCU) regulates both STIM1 activation y SOCE maintain by staying clear of its Ca2+-dependent slow inactivation19,20. GDAP1-KD cells and motoneurons from Gdap1-KO mice21 have uno reduced SOCE activity, associated with reduced SOCE-driven calcium absorb in mitochondria. This to be not as result of an intrinsic defect in mitochondrial calcium uptake yet to ns misallocation that mitochondria nearby to the subplasmalemmal sites15. Lessened SOCE activity in GDAP1-KD cells to be attributed to a Ca2+ induced inactivation that SOCE early to ns lack of Ca2+ uptake by adjacent mitochondria15. Junctophilin-1 (JPH1) protein, encoded by un GDAP1 gene modifier, plays ns role in Ca2+ homeostasis, y is maybe to gain back SOCE activity in GDAP1-KD cells. Ns presence the mutations in both gene (JPH1 y GDAP1) has actually been associated with uno more significant phenotype22.

The duty of SOCE has actually been related to ER-Ca2+ refilling23,24. In hippocampal neurons, SOCE has been shown to be essential for preserving ER-Ca2+ levels, which room continuously lost at rest23. We have actually observed that GDAP1-KD or Gdap1-KO cells have actually lower ER-Ca2+ levels21,22 linked with the defect in SOCE.

The aim of ns present examine is come explore the functional after-effects of impaired SOCE task in mitochondrial duty of GDAP1 deficient cells. Current findings have actually revealed new roles the calcium and its pathway-specific interaction with mitochondria in bioenergetics. For example, basal respiration reduce in cells lacking MCUR125, un putative regulator of los MCU (but check out ref. 26), in cells con lower mitochondrial Ca2+ transients upon stimulation25, or in cells lacking IP3 receptor or incubated with antagonists that IP3 receptors in which the lack of procesión Ca2+ stimulates autophagy27,28. In addition, workload-induced stimulation the respiration relies upon Ca2+ signaling in mitochondria, as displayed in neurons doing not have Ca2+-regulated AGC1/Aralar, ns Ca2+-dependent ingredient of ns malate aspartate shuttle29,30, and cardiomyocytes doing not have MCU31,32, but not in other studies33. This raises ns possibility that diminished SOCE activity from GDAP1 deficiency impacts on neuronal respiration y thereby may influence ATP manufacturing in ns affected neurons. Therefore, we have explored this possibility in neuroblastoma. In addition, we have studied the effects that GDAP1 pathological missense mutations in SOCE activity and SOCE-induced stimulation that respiration.

The results donar that GDAP1 deficiency outcomes in un defect that SOCE activity y ER- Ca2+ levels, with ns decrease in SOCE-stimulated respiration i m sorry is reproduced by recessive mutations situated in ns α-loop region of GDAP1 connected in mitochondrial movement, however not by other mutations. Ns specificity of these defects for different mutants may aid in understanding the pathogenic instrument of CMT.

Ca2+ signaling is required to upregulate respiration in response to SOCE

Neuroblastoma SH-SY5Y cell gestión can experience comprehensive Ca2+ influx through SOCE channels15. Los role of Ca2+ in tuning ATP production to ATP demand in excitable cells has been well-known for a long time34,35,36,37, y recently, Ca2+ has been shown to cooperate in adjusting coupled respiration to ATP demand under ns workloads induced by carbachol, high K+ depolarization or veratridine in neurons29,30,38. We analyzed even if it is SOCE-driven Ca2+ signals stimulate mitochondrial respiration in direccion SH-SY5Y pLKO neuroblastoma cells formerly described15. To this end, SOCE was triggered by carbachol, i m sorry mobilizes ER-Ca2+ with activation the IP3 receptors, followed by ns addition of 2 mM CaCl2. Ca2+ strongly created respiration (Fig. 1A), largely coupled respiration, together it was greatly inhibited by oligomycin (Fig. 1B). In the absence of exterior Ca2+ (vehicle), los increase in oxygen intake rate (OCR) was no observed (Fig. 1A). SOCE-induced stimulation that respiration was about 140% of early stage values, smaller than los maximal respiration obtained after uncoupler addition (Fig. 1C).


(A) Oxygen intake rate to express as percent of basal OCR in direccion pLKO cell showing los sequential injection the carbachol (Cch, 50 μM), automobile (Veh) or Ca2+ (2 mM) y metabolic inhibitors: oligomycin (Olig, 6 μM) and antimycin A/rotenone (Ant/Rot, 1 μM/1 μM) at los indicated hora points. (B) Quantification of oligomycin perceptible OCR expressed as percent of basal OCR in control pLKO cells. Los effect that calcium was far-ranging (n = 27, obtained representar at least ocho independent experiments). (C) Oxygen consumption rate to express as percentage of basal OCR in control pLKO cells at los time of auto addition. Sequential injection: vehicle, oligomycin, DNP (0.25 mM) y antimycin A/rotenone at ns indicated tiempo points. (D) SOCE-stimulation that respiration in absence or existence of BAPTA-AM (50, veinticinco or 10 μM). Oxygen usage rate express as portion of OCR delaware carbachol addition (Cch, 50 μM) in Ca2+-free medium. (E) Quantification that % OCR 6 min after calcium addition, (n = 3–12, from at least tres independent experiments). All datos are expressed together mean ± SEM. Method were contrasted using one-way and two-way ANOVA, *p posthoc Bonferroni test.

We próximo studied even if it is SOCE-stimulated respiration was due to rise in ATP need or through un direct result of cytosolic Ca2+ ~ above oxidative phosphorylation. Come this end, control neuroblastoma cells to be preincubated with different concentration of BAPTA-AM, a rapid intracellular Ca2+ chelator39 prior to measuring SOCE-stimulated respiration. BAPTA loading prevents cytosolic Ca2+ signals however does not adjust Ca2+ inflow through SOCE channels and thereby maintains los SOCE-induced workload29. In BAPTA-AM (50 y 25 μM) loaded cells Ca2+ stimulation the respiration was abolished during ns first 3 min after Ca2+ readmission (Fig. 1D), y the stimulation observed thereafter was much reduced in los presence of los chelator 보다 in its absence. A bajo chelator concentration (10 μM) had smaller, yet significant effects on Ca2+ stimulation respiration (Fig. 1D,E). Therefore, ns results suggest that Ca2+ signaling itself v regulation of mitochondrial respiration is required to pair respiration to SOCE activity.

Mitochondrial Ca2+ absorb regulates SOCE task in neuroblastoma cells

Mitochondrial taking care of of Ca2+ entry v capacitative calcium channels has been displayed to regulate SOCE activity by preventing Ca2+-dependent slow inactivation17,18,19,20. To investigate los role that mitochondrial Ca2+ absorb in modulation that SOCE in neuroblastoma cells, we studied ns effect that MCU knockdown. Neuro-2a cells were transfected con plasmids comprise Mcu-directed small hairpin RNA (shRNA) or non-target direccion sequence (scrambled) along con mCherry, to determine transfected cells40, and studied 72 hours later. This resulted in uno drop of MCU protein levels to 56.2 ± 8.3% of direccion values (Fig. 2A). i signal evoked by ATP were the same in scrambled or Mcu-KD cell (Fig. 2B). However, Ca2+ absorb in mitochondria (Camit) in an answer to this signals, studied with 4mt-D3cpv, un FRET calcium indicator target to the mitochondrial matrix41, was rather different. Ca2+ absorb in Mcu-KD was much lower than in scrambled mitochondria (Fig. 2B).

Figure 2: Mitochondrial Ca2+ uptake throughout SOCE and SOCE-stimulation that respiration is lessened in GDAP1-KD cells.


(A) analysis of MCU level by western blot. Protein extracts were acquired 72 hours after transfection that N2a cells with either shScr or shMcu. Primary antibodies supplied were α-MCU and α-βATPase as a control. MCU protein level drop to 56, 2 ± 8, 3% of direccion values. (B) Fura-2 i signals and 4mt-D3cpv mitochondrial calcium signals in N2a cell transfected con shScr or shMcu upon addition of 25 μM ATP wherein indicated. (C) Lyn-D3cpv subplasmalemmal Ca2+ signals were measured in N2a cells transfected con shScr or shMcu upon addition of 2 mM Ca2+ in Ca2+-free medium with 5 μM Thapsigargin (Tg). Datos were obtained from tres independent experiment (n = 9–16 cells). (D) Quantification of SOCE amplitude as ΔRatio (F510/F440) ± SEM for each condition. (E) SOCE response in control pLKO y GDAP1-KD neuroblastoma cells, in presence or lack of DNP (0.25 mM). Fura-2 i signals to be measured upon addition of 5 μM Tg in Ca2+ -free medium and dos mM CaCl2 wherein indicated. DNP was added 2 min before Ca2+ addition. Traces were obtained averaging in ~ least doscientos cincuenta cells desde at least cuatro independent experiments. (F) Quantification the SOCE amplitude as ΔRatio (F340/F380) ± SEM for each cell line and condition. (G) Oxygen usage rate expressed as portion of basal OCR in direccion pLKO y GDAP1-KD cells, showing ns sequential injection that carbachol (Cch, 50 μM), Ca2+ (2 mM) y metabolic inhibitors. (H,I) Quantification that % OCR 6 min after carbachol addition and 3 min after calcium enhancement respectively. Data were obtained desde at least ocho independent experiments (n = 27–50). All datos are normalized to ns initial values y are expressed as mean ± SEM. Method were contrasted using one-way or two-way ANOVA, *p posthoc Bonferroni test.

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We siguiente studied ns effects that MCU silencing top top Ca2+ entry with SOCE channels. We used the genetically encoded calcium indicator Lyn-D3cpv i m sorry is target to the plasma membrane41 in order come study transforms in Ca2+ at ns plasma membrane boundary, i.e, ns site the SOCE. Personaje 2C,D dando that Ca2+ inflow ~ above SOCE activation con thapsigargin was lessened in Mcu-KD cells compared con scrambled sequences.

To determine whether lessened SOCE in SH-SY5Y GDAP1-KD cells is because of an disability in mitochondrial Ca2+ handling, we studied Ca2+ influx v SOCE channels in control y the GDAP1-KD clone G4 previously described15 in existence of 0.25 mM 2,4-dinitrophenol (DNP), which collapses los mitochondrial membrane potential y prevents mitochondrial Ca2+ uptake. In control pLKO cells, DNP exposure caused uno decreased SOCE, i beg your pardon was diminished to los level that GDAP1-KD cell gestión (Fig. 2E,F). In contrast, DNP exposure did no affect los amplitude that SOCE in GDAP1-KD cells, a result regular with ns hypothesis the GDAP1 deficiency prevents appropriate positioning of mitochondria and adequate handling of SOCE-driven Ca2+ inflow, in order to causing un decrease in SOCE15. Interestingly, DNP treatment in humanidad SH-SY5Y neuroblastoma cells caused uno decrease in SOCE task to 71.5 ± 2.8% of direccion values and MCU silencing in computer mouse N2a neuroblastoma cells resulted in a raza decrease to 79 ± 6% of los levels in direccion cells treated with scrambled MCU sequences. These outcomes support that uno failure to take up Ca2+ in mitochondria próximo to los sites that SOCE opening causes los early inactivation the SOCE in GDAP1 deficient cells.

GDAP1 silencing impairs SOCE-driven stimulation that respiration

We next tested los effect that GDAP1-KD ~ above SOCE-stimulation that respiration. Figure 2G mirrors that OCR stimulation caused by Ca2+ addition after ER-Ca2+ mobilization by carbachol is plainly lower in GDAP1-KD than direccion pLKO cells. Ca2+-dependent stimulation of respiration 3 min delaware Ca2+ addition, a tiempo at which los SOCE-induced boost in i levels turn off (Fig. 2C,E), was 27.9 ± 2.4% above ns initial worths in control cells and 16.0 ± 0.7% in GDAP1 deficient cells (Fig. 2G,H). Interestingly, los increase in respiration caused by carbachol enhancement in ns Ca2+-free tool is also reduced in ns GDAP1 deficient cells (Fig. 2G,I), a result described by reduced ER-Ca2+ levels observed in GDAP1-KD cells22.

Clinical GDAP1-CMT mutations have different effects on SOCE activity

GDAP1 has two GST domain names separated by a region referred to as α-loop, and a C-terminal transmembrane domain. We have actually previously discovered that the α-loop is the protein domain whereby caytaxin and RAB6B interact15. This says that mutations in ns α-loop or also in ns GST domains might affect ns interaction con other protein partners, if mutations in los transmembrane domain might be regarded failures in mitochondrial anchoring as proposed previously42. Come address the role of this GDAP1 mutant protein in restoring SOCE task in GDAP1-KD cells, us selected a battery the dominant y recessive missense mutations located along los whole protein. Because that recessive mutations us selected p.R120Q, p.R282C y p.L344R together mutations outside the α-loop43,44,45 y p.S130C, p.R161H and p.N178S inside los α-loop46,47. We likewise selected p.R120W, p.H123R and p.T157P as uno dominant mutations6,48,49 (Fig. 3A).

Figure 3: Pathological GDAP1 missense mutations donar different effects on SOCE and ER-Ca2+ content depending on ns mode the inheritance and their domain-location in ns protein.


(A) Schematic watch of ns GDAP1 missense mutations selected for ns experiment. (B) SOCE rescue in GDAP1-KD cells (black line) transfected with pCAGIG-GDAP1 (brown line). The control pLKO cell línea was transfected with pCAGIG north vector and used as un control. Fura-2 i signals to be measured upon enhancement of 5 μM TG in Ca2+-free medium y 2 mM Ca2+ wherein indicated. (CE) SOCE in GDAP1-KD cell expressing recessive mutations situated outside los protein-protein interaction domain α-loop (C), recessive mutations located inside ns α-loop domain (D) and dominant mutations (E). Fura-2 i signals to be measured upon enhancement of 5 μM TG in Ca2+-free medium and 2 mM Ca2+ whereby indicated. Quantification that SOCE amplitude together ΔRatio (F340/F380) is displayed in (C’,D’ y E’). (FH) comparison of ER-Ca2+ content by measure ionomycin-induced Ca2+ release in ns GDAP1-KD cell line or in ns GDAP1-KD cell line overexpressing the indicated plasmids with recessive mutations exterior (F) and inside los α-loop (G), y dominant mutations (H). Quantification the ionomycin-induced Ca2+ release amplitude together ΔRatio (F340/F380) is presented in (F’,G’ and H’). Fura-2 i signals were measured upon addition 5 μM ionomycin in Ca2+-free medium. In all los experiments, much more than 50 transfected cells were analyzed in 5 independent experiments. Data are normalized to the initial values and are expressed together mean ± SEM. Method were compared using one-way ANOVA test. *p posthoc Bonferroni test.

The effect related to each mutation to be tested on SH-SY5Y GDAP1-KD cells after transfection with un bicistronic pCAGIG plasmid, which codified for the GDAP1 mutant and GFP, choosing for evaluation only transfected cells. An north vector (only GFP) and a vector con wild type GDAP1 were used as controls. SOCE was set off by emptying ER-Ca2+ con thapsigargin (TG) prior to activate SOCE with dos mM CaCl2. As GDAP1 silencing results in an increase in relaxing cytosolic Ca2+15, every responses were normalized to los basal level. The expression of north vector walk not alter SOCE task (compare traces of direccion cell line pLKO con that the GDAP1, both express GFP (Fig. 3B)). Overexpression that WT GDAP1 protein does not recoup SOCE activity at ns level of control pLKO cells. Therefore, to address los effect of GDAP1 missense mutations us compared los responses of each mutant with cells overexpressing WT GDAP1 protein.

The GDAP1 impact on SOCE was different depending on los type the mutation. Recessive GDAP1 mutations situated inside los α-loop to be unable come compensate for the lack the GDAP1 in SOCE activity, indicating a complete loss of function. Neither p.S130C, p.R161H nor p.N178S can rescue ns defect in SOCE and acted as the empty vector (Fig. 3D,D’). However, recessive mutations located external loop, in TM (p.L344R) or GST domains (pR282C, R120Q) have los same effect on SOCE as GDAP1 (Fig. 3C,C’). In contrast, overexpression of leading GDAP1 missense mutations produced a completely various effect (Fig. 3E,E’). P.H123R and p.T157P, in the α-loop region, and p.R120W in a GST domain, every one of them con an inherited leading pattern, cause uno significant rise in SOCE activity compared to wild type GDAP1, suggesting a gain of duty of this mutations.

Taken together, the results suggest that recessive y dominant mutations in ns α-loop and N-terminal flanking GST domain law as lack of duty or get of duty mutants respectively, possibly through their intervención with protein-protein interactions within the α-loop domain. These interactions, possibly via caytaxin and RAB6B, space likely forced for los adequate localization the mitochondria close come SOCE sites and their perturbation by mutations in GDAP1 is more than likely responsible for ns inhibition of SOCE activity or stimulation the abnormal SOCE. On los other side, recessive mutations in other positions of los protein may act in un different way y do not admitir any impairment of SOCE activity. This is no surprising given los number that functions and interacting partner of GDAP1, and suggest that mutations in regions of the protein other than los α-loop result in pathogenesis through special needs of their certain interactions. In agreement con this specificity, los p.R161H recessive mutation in los α-loop which we now show to impair SOCE task did not have any kind of effect top top mitochondrial fission9.

As GDAP1 missense mutations within los α-loop domain reducir SOCE activity, y SOCE is concerned filling of ER-Ca2+, these mutations may affect ER-Ca2+ levels. To attend to this possibility, we evaluated los Ca2+ transients induced by discharging ER-Ca2+ con ionomycin in a Ca2+-free media. Overexpression in GDAP1-KD cell of WT GDAP1, or any of los recessive missense mutant proteins el fin of los α-loop (Fig. 3F,F’) or any kind of of ns dominant mutant proteins (Fig. 3H,H’), resulted in similar Ca2+ transients obtained by discharge the ER-Ca2+. In contrast, transient expression the recessive GDAP1 mutant proteins with changes located inside the α-loop result in un decrease in los Ca2+ peak, saying that reduced SOCE activity results in ns reduced volume to refill ns ER with Ca2+ (Fig. 3G,G’).

Impaired mitochondrial localization at ns suplasmalemmal domain in GDAP1 mutants

Our results are consistent with uno major duty of mitochondria in managing SOCE task in neuroblastoma cells. Us previously discovered that mitochondria relocate to los suplasmalemmal (SP) domain (defined together 0–2 μm from plasma membrane) delaware ER-Ca2+ depletion in control but no in GDAP1-silenced neuroblastoma cells15. In order come address los mechanisms whereby the different mutations impact SOCE activity, we have actually studied ns localization that mitochondria in relation to SP microdomains in basal problems and after ER-Ca2+ depletion in neuroblastoma cell expressing leading or recessive mutations in ns α-loop. Un Orai1::CFP expression vector was offered to mark of los plasma membrane while the c-myc epitope from GDAP1-c-myc expression plasmids served as marker for mitochondria in immunofluorescence assays. The mitochondrial fluorescence distribution between opposite plasma membranes within the SP y the centrar cell area was analyzed (Supplementary Fig. S2).

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As presented previously15, delaware ER-Ca2+ mobilization, mitochondria representar GDAP1-silenced cells expressing an empty vector fail to localize at SP, bring about a similar mitochondrial distribution in basal y SOCE-activation conditions (Fig. 4A,B). Re-expression that WT GDAP1 protein enabled mitochondria to be positioned in SP after ER-Ca2+ depletion (Figs 4A,g,h and 5B), when overexpression of the recessive mutation p.R161H had actually an effect similar to silencing the GDAP1, alguno relocation that mitochondria to SP (Fig. 4A,B). Mitochondria desde cells overexpressing ns dominant mutation execute not relocalize to SP delaware ER-Ca2+ depletion (Fig. 4B) but dando a surprisingly higher percentage that mitochondria close to SP debajo basal conditions (Fig. 4A,m). This difference is much more pronounced in the interval from 0 to 1 μm representar the plasma membrane (Fig. 4C), and suggests that this abnormal mitochondrial localization, closer come plasma membrane, may be associated with the higher SOCE activity caused by ns dominant mutant.