CoQ deficiency causes disruption of mitochondrial sulfide oxidation, a new pathomechanism associated with this syndrome

Abstract

Coenzyme Q (CoQ) is a key component of the mitochondrial respiratory chain, but it also has several other functions in the cellular metabolism. One of them is to function as an electron carrier in the reaction catalyzed by sulfide:quinone oxidoreductase (SQR), which catalyzes the first reaction in the hydrogen sulfide oxidation pathway. Therefore, SQR may be affected by CoQ deficiency. Using human skin fibroblasts and two mouse models with primary CoQ deficiency, we demonstrate that severe CoQ deficiency causes a reduction in SQR levels and activity, which leads to an alteration of mitochondrial sulfide metabolism. In cerebrum of Coq9^R239X mice, the deficit in SQR induces an increase in thiosulfate sulfurtransferase and sulfite oxidase, as well as modifications in the levels of thiols. As a result, biosynthetic pathways of glutamate, serotonin, and catecholamines were altered in the cerebrum, and the blood pressure was reduced. Therefore, this study reveals the reduction in SQR activity as one of the pathomechanisms associated with CoQ deficiency syndrome.

Keywords: COX; SQR; blood pressure; glutathione; mitochondrial disease.

Figure 1. Hydrogen sulfide oxidation pathway in mammalian mitochondria

SQR, sulfide:quinone oxidoreductase; TR, thiosulfate reductase; SDO, sulfur deoxygenase or ETHE1; SO, sulfite oxidase or SUOX; TST, thiosulfate sulfurtransferase or rhodanase.

Figure 2. SQR levels and activity depend on CoQ levels in mice tissues

1. A–H

   Sqr mRNA levels (A–C), SQR protein levels (D–F), and SQR activity (G, H) in cerebrum (A, D), kidneys (B, E, G), and muscle (C, F, H) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice. Note that SQR Western blots were performed in isolated cerebral mitochondria due to the low levels of this protein in cerebrum. In kidneys and muscle, the Western blots were performed in tissue homogenates. Data are expressed as mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; Coq9 ^R239X and Coq9 ^Q95X mice versus Coq9 ^+/+ mice. ^# P < 0.05; ^## P < 0.01; ^### P < 0.001; Coq9 ^R239X versus Coq9 ^Q95X mice (one‐way ANOVA with a Tukey's post hoc test; n = 5–9 for each group).

Source data are available online for this figure.

Figure 3. Human skin fibroblasts and mouse tissues with primary CoQ₁₀ deficiency exhibit increased SQR protein levels after exogenous CoQ₁₀ supplementation

1. A

   Levels of CoQ₁₀ in fibroblasts of controls (C) and patients (P1‐4) with primary CoQ₁₀ deficiency.

2. B

   Levels of SQR protein in fibroblasts of controls (C) and patients (P1‐4) with primary CoQ₁₀ deficiency cultured without (vehicle) and with 5 μM of CoQ₁₀ (+ CoQ₁₀) during 1 day or 7 days.

3. C, D

   Total CoQ levels (CoQ₉ + CoQ₁₀) in kidneys (C) and muscle (D) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^R239X + ubiquinol‐10 (Q₁₀H₂) mice.

4. E, F

   Levels of SQR protein in kidneys (E) and muscle (F) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^R239X + ubiquinol‐10 (Q₁₀H₂) mice.

Data information: Data are expressed as mean ± SD. **P < 0.01; ***P < 0.001; patients versus controls, as well as Coq9 ^R239X versus Coq9 ^+/+ mice. ⁺ P < 0.05; ⁺⁺ P < 0.01; ⁺⁺⁺ P < 0.001; + CoQ₁₀ versus vehicle (one‐way ANOVA with a Tukey's post hoc test; n = 3–5 for each group). Source data are available online for this figure.

Figure 4. Changes in the proteins involved in the mitochondrial sulfide oxidation pathway in response to SQR deficiency in Coq9 ^R239X mice

1. A–C

   TST protein levels in cerebrum (A), kidneys (B), and muscle (C) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice.

2. D–F

   TST activity in cerebrum (D), kidneys (E), and muscle (F) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice.

3. G–I

   ETEH1 (SDO) protein levels in cerebrum (G), kidneys (H), and muscle (I) of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice.

4. J–L

   SUOX protein levels in cerebrum (J), kidneys (K), and muscle (L) of Coq9 ^+/+, Coq9 ^R239X and Coq9 ^Q95X mice.

Data information: Images in panels (C, F, and I) were obtained from the same membrane after stripping and re‐blotting. Data are expressed as mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; Coq9 ^R239X and Coq9 ^Q95X mice versus Coq9 ^+/+ mice. ^# P < 0.05; ^## P < 0.01; ^### P < 0.001; Coq9 ^R239X versus Coq9 ^Q95X mice (one‐way ANOVA with a Tukey's post hoc test; n = 5–9 for each group). Source data are available online for this figure.

Figure 5. Tissue levels of sulfides in CoQ‐deficient mice

1. Quantification of sulfide levels in cerebrum and kidneys of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice. Data are expressed as mean ± SD. *P < 0.05; Coq9 ^R239X and Coq9 ^Q95X mice versus Coq9 ^+/+ mice. ^## P < 0.01; Coq9 ^R239X versus Coq9 ^Q95X mice (one‐way ANOVA with a Tukey's post hoc test; n = 5–10 for each group).

2. Qualitative measurement of hydrogen sulfide in cerebrum and kidneys of Coq9 ^+/+ and Coq9 ^R239X mice.

Figure 6. Glutathione system and neurotransmitters biosynthesis are compromised in cerebrum of Coq9 ^R239X mice

1. A

   Total GSH in cytosol and mitochondria of cerebrum of Coq9 ^+/+ and Coq9 ^R239X mice.

2. B

   Cytosolic GPx and GRd activities in cerebrum of Coq9 ^+/+ and Coq9 ^R239X mice.

3. C, D

   Levels of GPx4 (C) and GRd (D) protein in cerebral homogenate of Coq9 ^+/+ and Coq9 ^R239X mice.

4. E

   Levels of L‐glutamate (L‐Glu), N‐acetylglutamate (NacGlu), L‐tryptophan (L‐Trp), 5‐HIAA, N‐acetyltryptophan (NALT), L‐tyrosine (L‐Tyr) in cerebrum of Coq9 ^+/+ and Coq9 ^R239X mice.

5. F

   Biosynthetic pathway of GSH, serotonin, and catecholamine.

Data information: Data are expressed as mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; Coq9 ^R239X mice versus Coq9 ^+/+ mice (t‐test; n = 5 for each group). Source data are available online for this figure.

Figure 7. Supplementation with an H₂S donor in wild‐type animals induces changes in neurotransmitters levels

1. A, B

   SQR (A) and TST (B) protein levels in human skin fibroblasts supplemented with the H₂S donor GYY4137.

2. C, D

   TST protein level in kidneys (C) and cerebrum (D) of Coq9 ^+/+ mice supplemented with the H₂S donor GYY4137.

3. E

   Levels of neurotransmitters in cerebrum of Coq9 ^+/+ mice supplemented with the H₂S donor GYY4137.

Data information: Images in panels (A and B) were obtained from the same membrane after stripping and re‐blotting. Data are expressed as mean ± SD. **P < 0.01; ***P < 0.001; Coq9 ^+/+ mice supplemented with GYY4137 versus Coq9 ^+/+ mice (t‐test; n = 4–6 for each group). Source data are available online for this figure.

Figure 8. COX activity in tissues from CoQ‐deficient mice

1. COX activity in cerebrum, kidneys, and muscle of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice. Data are expressed as mean ± SD (one‐way ANOVA with a Tukey's post hoc test; n = 3–6 for each group).

2. Images COX histochemistry in gastrocnemius of Coq9 ^+/+, Coq9 ^R239X, and Coq9 ^Q95X mice; scale bar: 100 μm.

Figure 9. Blood pressure and heart rate in Coq9 ^R239X mice

1. Systolic, diastolic, and mean blood pressure in Coq9 ^+/+ and Coq9 ^R239X mice.

2. Heart rate in Coq9 ^+/+ and Coq9 ^R239X mice.

Data information: Data are expressed as mean ± SD. **P < 0.01; Coq9 ^R239X mice versus Coq9 ^+/+ mice (t‐test; n = 5 for each group).