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Altered Ca2+ kinetics associated with α-actinin-3 deficiency may explain positive selection for ACTN3 allele in human evolution.

Head SI, Chan S, Houweling PJ, Quinlan KG, Murphy R, Wagner S, Friedrich O, North KN - PLoS Genet. (2015)

Bottom Line: Over 1.5 billion people lack the skeletal muscle fast-twitch fibre protein α-actinin-3 due to homozygosity for a common polymorphism (R577X) in the ACTN3 gene. α-Actinin-3 deficiency is detrimental to sprint performance in elite athletes and beneficial to endurance activities.Prolonged exposure to cold can also induce changes in skeletal muscle similar to those observed with endurance training, and changes in Ca2+ handling by the sarcoplasmic reticulum (SR) are a key factor underlying these adaptations.On this basis, we explored the effects of α-actinin-3 deficiency on Ca2+ kinetics in single flexor digitorum brevis muscle fibres from Actn3 KO mice, using the Ca2+-sensitive dye fura-2.

View Article: PubMed Central - PubMed

Affiliation: School of Medical Sciences, University of New South Wales, Sydney, Australia.

ABSTRACT
Over 1.5 billion people lack the skeletal muscle fast-twitch fibre protein α-actinin-3 due to homozygosity for a common polymorphism (R577X) in the ACTN3 gene. α-Actinin-3 deficiency is detrimental to sprint performance in elite athletes and beneficial to endurance activities. In the human genome, it is very difficult to find single-gene loss-of-function variants that bear signatures of positive selection, yet intriguingly, the ACTN3 variant has undergone strong positive selection during recent evolution, appearing to provide a survival advantage where food resources are scarce and climate is cold. We have previously demonstrated that α-actinin-3 deficiency in the Actn3 KO mouse results in a shift in fast-twitch fibres towards oxidative metabolism, which would be more "energy efficient" in famine, and beneficial to endurance performance. Prolonged exposure to cold can also induce changes in skeletal muscle similar to those observed with endurance training, and changes in Ca2+ handling by the sarcoplasmic reticulum (SR) are a key factor underlying these adaptations. On this basis, we explored the effects of α-actinin-3 deficiency on Ca2+ kinetics in single flexor digitorum brevis muscle fibres from Actn3 KO mice, using the Ca2+-sensitive dye fura-2. Compared to wild-type, fibres of Actn3 KO mice showed: (i) an increased rate of decay of the twitch transient; (ii) a fourfold increase in the rate of SR Ca2+ leak; (iii) a threefold increase in the rate of SR Ca2+ pumping; and (iv) enhanced maintenance of tetanic Ca2+ during fatigue. The SR Ca2+ pump, SERCA1, and the Ca2+-binding proteins, calsequestrin and sarcalumenin, showed markedly increased expression in muscles of KO mice. Together, these changes in Ca2+ handling in the absence of α-actinin-3 are consistent with cold acclimatisation and thermogenesis, and offer an additional explanation for the positive selection of the ACTN3 577X allele in populations living in cold environments during recent evolution.

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Expression of major Ca2+-handling proteins in muscles of WT and Actn3 KO mice.Protein expression analysis of the EDL (A), FDB (B) and quadriceps (C) muscles of WT and Actn3 KO mice. Representative Western blots are shown with densitometry values normalised to total protein and the average of all WT samples. A significant increase in SERCA1 was observed in the EDL, FDB and quadriceps, along with an increase in calsequestrin (CSQ1) in the EDL and sarcalumenin (SAR) in the FDB and quadriceps. No change in RyR1 and DHPR expression were seen in the EDL and parvalbumin (PARVALB) is unchanged in both the EDL and FDB. A total of 6 WT and 6 Actn3 KO EDL, 3 WT and 3 Actn3 KO FDB and 4 WT and 4 Actn3 KO quadriceps muscles were analysed. Statistical analyses were performed using the Mann-Whitney U non-parametric test (* denotes p < 0.05).
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pgen.1004862.g005: Expression of major Ca2+-handling proteins in muscles of WT and Actn3 KO mice.Protein expression analysis of the EDL (A), FDB (B) and quadriceps (C) muscles of WT and Actn3 KO mice. Representative Western blots are shown with densitometry values normalised to total protein and the average of all WT samples. A significant increase in SERCA1 was observed in the EDL, FDB and quadriceps, along with an increase in calsequestrin (CSQ1) in the EDL and sarcalumenin (SAR) in the FDB and quadriceps. No change in RyR1 and DHPR expression were seen in the EDL and parvalbumin (PARVALB) is unchanged in both the EDL and FDB. A total of 6 WT and 6 Actn3 KO EDL, 3 WT and 3 Actn3 KO FDB and 4 WT and 4 Actn3 KO quadriceps muscles were analysed. Statistical analyses were performed using the Mann-Whitney U non-parametric test (* denotes p < 0.05).

Mentions: As we have demonstrated that [Ca2+]i kinetics are altered in Actn3 KO fibres, it was important to examine the expression of the major proteins involved in Ca2+ release and re-uptake. Fig. 5 shows results of Western blots performed on extensor digitorum longus (EDL), FDB and quadriceps muscles from WT and Actn3 KO mice. The major proteins involved in the rise of the Ca2+ transient are the dihydropyridine-receptor voltage sensor (DHPR) and the ryanodine-receptor Ca2+-release channel (RyR1) [28]. There was no difference between WT and KO in the expression of either of these proteins (Fig. 5A). The decay of the Ca2+ transient in fast-twitch fibres involves the binding of Ca2+ to myoplasmic buffers, the main one being parvalbumin, and the re-uptake of Ca2+ by the SR [28]. In fast-twitch fibres the SR Ca2+ pump is SERCA1, while calsequestrin and sarcalumenin are Ca2+-binding proteins within the SR lumen [29,30]. There was no difference between WT and KO in parvalbumin expression (Fig. 5A and B). However, muscles from Actn3 KO mice showed significantly increased expression of SERCA1, calsequestrin and sarcalumenin (Fig. 5A, B and C).


Altered Ca2+ kinetics associated with α-actinin-3 deficiency may explain positive selection for ACTN3 allele in human evolution.

Head SI, Chan S, Houweling PJ, Quinlan KG, Murphy R, Wagner S, Friedrich O, North KN - PLoS Genet. (2015)

Expression of major Ca2+-handling proteins in muscles of WT and Actn3 KO mice.Protein expression analysis of the EDL (A), FDB (B) and quadriceps (C) muscles of WT and Actn3 KO mice. Representative Western blots are shown with densitometry values normalised to total protein and the average of all WT samples. A significant increase in SERCA1 was observed in the EDL, FDB and quadriceps, along with an increase in calsequestrin (CSQ1) in the EDL and sarcalumenin (SAR) in the FDB and quadriceps. No change in RyR1 and DHPR expression were seen in the EDL and parvalbumin (PARVALB) is unchanged in both the EDL and FDB. A total of 6 WT and 6 Actn3 KO EDL, 3 WT and 3 Actn3 KO FDB and 4 WT and 4 Actn3 KO quadriceps muscles were analysed. Statistical analyses were performed using the Mann-Whitney U non-parametric test (* denotes p < 0.05).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4295894&req=5

pgen.1004862.g005: Expression of major Ca2+-handling proteins in muscles of WT and Actn3 KO mice.Protein expression analysis of the EDL (A), FDB (B) and quadriceps (C) muscles of WT and Actn3 KO mice. Representative Western blots are shown with densitometry values normalised to total protein and the average of all WT samples. A significant increase in SERCA1 was observed in the EDL, FDB and quadriceps, along with an increase in calsequestrin (CSQ1) in the EDL and sarcalumenin (SAR) in the FDB and quadriceps. No change in RyR1 and DHPR expression were seen in the EDL and parvalbumin (PARVALB) is unchanged in both the EDL and FDB. A total of 6 WT and 6 Actn3 KO EDL, 3 WT and 3 Actn3 KO FDB and 4 WT and 4 Actn3 KO quadriceps muscles were analysed. Statistical analyses were performed using the Mann-Whitney U non-parametric test (* denotes p < 0.05).
Mentions: As we have demonstrated that [Ca2+]i kinetics are altered in Actn3 KO fibres, it was important to examine the expression of the major proteins involved in Ca2+ release and re-uptake. Fig. 5 shows results of Western blots performed on extensor digitorum longus (EDL), FDB and quadriceps muscles from WT and Actn3 KO mice. The major proteins involved in the rise of the Ca2+ transient are the dihydropyridine-receptor voltage sensor (DHPR) and the ryanodine-receptor Ca2+-release channel (RyR1) [28]. There was no difference between WT and KO in the expression of either of these proteins (Fig. 5A). The decay of the Ca2+ transient in fast-twitch fibres involves the binding of Ca2+ to myoplasmic buffers, the main one being parvalbumin, and the re-uptake of Ca2+ by the SR [28]. In fast-twitch fibres the SR Ca2+ pump is SERCA1, while calsequestrin and sarcalumenin are Ca2+-binding proteins within the SR lumen [29,30]. There was no difference between WT and KO in parvalbumin expression (Fig. 5A and B). However, muscles from Actn3 KO mice showed significantly increased expression of SERCA1, calsequestrin and sarcalumenin (Fig. 5A, B and C).

Bottom Line: Over 1.5 billion people lack the skeletal muscle fast-twitch fibre protein α-actinin-3 due to homozygosity for a common polymorphism (R577X) in the ACTN3 gene. α-Actinin-3 deficiency is detrimental to sprint performance in elite athletes and beneficial to endurance activities.Prolonged exposure to cold can also induce changes in skeletal muscle similar to those observed with endurance training, and changes in Ca2+ handling by the sarcoplasmic reticulum (SR) are a key factor underlying these adaptations.On this basis, we explored the effects of α-actinin-3 deficiency on Ca2+ kinetics in single flexor digitorum brevis muscle fibres from Actn3 KO mice, using the Ca2+-sensitive dye fura-2.

View Article: PubMed Central - PubMed

Affiliation: School of Medical Sciences, University of New South Wales, Sydney, Australia.

ABSTRACT
Over 1.5 billion people lack the skeletal muscle fast-twitch fibre protein α-actinin-3 due to homozygosity for a common polymorphism (R577X) in the ACTN3 gene. α-Actinin-3 deficiency is detrimental to sprint performance in elite athletes and beneficial to endurance activities. In the human genome, it is very difficult to find single-gene loss-of-function variants that bear signatures of positive selection, yet intriguingly, the ACTN3 variant has undergone strong positive selection during recent evolution, appearing to provide a survival advantage where food resources are scarce and climate is cold. We have previously demonstrated that α-actinin-3 deficiency in the Actn3 KO mouse results in a shift in fast-twitch fibres towards oxidative metabolism, which would be more "energy efficient" in famine, and beneficial to endurance performance. Prolonged exposure to cold can also induce changes in skeletal muscle similar to those observed with endurance training, and changes in Ca2+ handling by the sarcoplasmic reticulum (SR) are a key factor underlying these adaptations. On this basis, we explored the effects of α-actinin-3 deficiency on Ca2+ kinetics in single flexor digitorum brevis muscle fibres from Actn3 KO mice, using the Ca2+-sensitive dye fura-2. Compared to wild-type, fibres of Actn3 KO mice showed: (i) an increased rate of decay of the twitch transient; (ii) a fourfold increase in the rate of SR Ca2+ leak; (iii) a threefold increase in the rate of SR Ca2+ pumping; and (iv) enhanced maintenance of tetanic Ca2+ during fatigue. The SR Ca2+ pump, SERCA1, and the Ca2+-binding proteins, calsequestrin and sarcalumenin, showed markedly increased expression in muscles of KO mice. Together, these changes in Ca2+ handling in the absence of α-actinin-3 are consistent with cold acclimatisation and thermogenesis, and offer an additional explanation for the positive selection of the ACTN3 577X allele in populations living in cold environments during recent evolution.

Show MeSH
Related in: MedlinePlus