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BK channel agonist represents a potential therapeutic approach for lysosomal storage diseases

View Article: PubMed Central - PubMed

ABSTRACT

Efficient lysosomal Ca2+ release plays an essential role in lysosomal trafficking. We have recently shown that lysosomal big conductance Ca2+-activated potassium (BK) channel forms a physical and functional coupling with the lysosomal Ca2+ release channel Transient Receptor Potential Mucolipin-1 (TRPML1). BK and TRPML1 forms a positive feedback loop to facilitate lysosomal Ca2+ release and subsequent lysosome membrane trafficking. However, it is unclear whether the positive feedback mechanism is common for other lysosomal storage diseases (LSDs) and whether BK channel agonists rescue abnormal lysosomal storage in LSDs. In this study, we assessed the effect of BK agonist, NS1619 and NS11021 in a number of LSDs including NPC1, mild cases of mucolipidosis type IV (ML4) (TRPML1-F408∆), Niemann-Pick type A (NPA) and Fabry disease. We found that TRPML1-mediated Ca2+ release was compromised in these LSDs. BK activation corrected the impaired Ca2+ release in these LSDs and successfully rescued the abnormal lysosomal storage of these diseases by promoting TRPML1-mediated lysosomal exocytosis. Our study suggests that BK channel activation stimulates the TRPML1-BK positive reinforcing loop to correct abnormal lysosomal storage in LSDs. Drugs targeting BK channel represent a potential therapeutic approach for LSDs.

No MeSH data available.


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BK upregulation reduces lipofuscin accumulation in NPA cells by promoting TRPML1-mediated Ca2+ release.(A,B) Abnormal lipofuscin accumulation in NPA human fibroblasts and its rescue by BK overexpression or NS1619 (15 μM, 16 h) treatment. Expression of TRPML1-DD/KK or Syt VII DN reversed the rescue effect of BK upregulation. More than 35 cells were analyzed for each condition. (C–E) Impaired ML-SA1 (10 μM)-mediated GECO-TRPML1 response in NPA human fibroblasts and its rescue by NS1619 (15 μM, ~60 s) pretreatment (C) or BK overexpression (D). Paxilline (PAX, 3 μM) treatment reversed the rescue effect of NS1619 or BK overexpression. (F,G) GECO-TRPML1 responses to GPN (200 μM) (F) and Ionomycin (1 μM) (G) were not altered in all the treatments, suggesting lysosomal Ca2+ content, or GECO-TRPML1 expression level was not affected.
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f6: BK upregulation reduces lipofuscin accumulation in NPA cells by promoting TRPML1-mediated Ca2+ release.(A,B) Abnormal lipofuscin accumulation in NPA human fibroblasts and its rescue by BK overexpression or NS1619 (15 μM, 16 h) treatment. Expression of TRPML1-DD/KK or Syt VII DN reversed the rescue effect of BK upregulation. More than 35 cells were analyzed for each condition. (C–E) Impaired ML-SA1 (10 μM)-mediated GECO-TRPML1 response in NPA human fibroblasts and its rescue by NS1619 (15 μM, ~60 s) pretreatment (C) or BK overexpression (D). Paxilline (PAX, 3 μM) treatment reversed the rescue effect of NS1619 or BK overexpression. (F,G) GECO-TRPML1 responses to GPN (200 μM) (F) and Ionomycin (1 μM) (G) were not altered in all the treatments, suggesting lysosomal Ca2+ content, or GECO-TRPML1 expression level was not affected.

Mentions: In Niemann-Pick type A (NPA) and type B (NPB) diseases, sphingomyelin accumulation in lysosomes due to insufficient activity of acid sphingomyelinase results in reduced TRPML1-mediated lysosomal Ca2+ release and lysosomal storage44101115. Given that BK promotes TRPML1-mediated lysosomal Ca2+ release, we hypothesize that BK upregulation rescues NPA phenotypes. As expected, NPA cells displayed increased lipofuscin autofluoresence, as compared to wild type human fibroblasts415, and this was rescued by BK overexpression or NS1619 (15 μM, 16 h) treatment (Fig. 6A,B). Expression of TRPML1-DD/KK or Syt VII DN inhibited the rescue effect of BK. Therefore, BK upregulation rescues lysosomal storage in NPA patient cells through facilitating TRPML1-mediated lysosomal exocytosis.


BK channel agonist represents a potential therapeutic approach for lysosomal storage diseases
BK upregulation reduces lipofuscin accumulation in NPA cells by promoting TRPML1-mediated Ca2+ release.(A,B) Abnormal lipofuscin accumulation in NPA human fibroblasts and its rescue by BK overexpression or NS1619 (15 μM, 16 h) treatment. Expression of TRPML1-DD/KK or Syt VII DN reversed the rescue effect of BK upregulation. More than 35 cells were analyzed for each condition. (C–E) Impaired ML-SA1 (10 μM)-mediated GECO-TRPML1 response in NPA human fibroblasts and its rescue by NS1619 (15 μM, ~60 s) pretreatment (C) or BK overexpression (D). Paxilline (PAX, 3 μM) treatment reversed the rescue effect of NS1619 or BK overexpression. (F,G) GECO-TRPML1 responses to GPN (200 μM) (F) and Ionomycin (1 μM) (G) were not altered in all the treatments, suggesting lysosomal Ca2+ content, or GECO-TRPML1 expression level was not affected.
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Related In: Results  -  Collection

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f6: BK upregulation reduces lipofuscin accumulation in NPA cells by promoting TRPML1-mediated Ca2+ release.(A,B) Abnormal lipofuscin accumulation in NPA human fibroblasts and its rescue by BK overexpression or NS1619 (15 μM, 16 h) treatment. Expression of TRPML1-DD/KK or Syt VII DN reversed the rescue effect of BK upregulation. More than 35 cells were analyzed for each condition. (C–E) Impaired ML-SA1 (10 μM)-mediated GECO-TRPML1 response in NPA human fibroblasts and its rescue by NS1619 (15 μM, ~60 s) pretreatment (C) or BK overexpression (D). Paxilline (PAX, 3 μM) treatment reversed the rescue effect of NS1619 or BK overexpression. (F,G) GECO-TRPML1 responses to GPN (200 μM) (F) and Ionomycin (1 μM) (G) were not altered in all the treatments, suggesting lysosomal Ca2+ content, or GECO-TRPML1 expression level was not affected.
Mentions: In Niemann-Pick type A (NPA) and type B (NPB) diseases, sphingomyelin accumulation in lysosomes due to insufficient activity of acid sphingomyelinase results in reduced TRPML1-mediated lysosomal Ca2+ release and lysosomal storage44101115. Given that BK promotes TRPML1-mediated lysosomal Ca2+ release, we hypothesize that BK upregulation rescues NPA phenotypes. As expected, NPA cells displayed increased lipofuscin autofluoresence, as compared to wild type human fibroblasts415, and this was rescued by BK overexpression or NS1619 (15 μM, 16 h) treatment (Fig. 6A,B). Expression of TRPML1-DD/KK or Syt VII DN inhibited the rescue effect of BK. Therefore, BK upregulation rescues lysosomal storage in NPA patient cells through facilitating TRPML1-mediated lysosomal exocytosis.

View Article: PubMed Central - PubMed

ABSTRACT

Efficient lysosomal Ca2+ release plays an essential role in lysosomal trafficking. We have recently shown that lysosomal big conductance Ca2+-activated potassium (BK) channel forms a physical and functional coupling with the lysosomal Ca2+ release channel Transient Receptor Potential Mucolipin-1 (TRPML1). BK and TRPML1 forms a positive feedback loop to facilitate lysosomal Ca2+ release and subsequent lysosome membrane trafficking. However, it is unclear whether the positive feedback mechanism is common for other lysosomal storage diseases (LSDs) and whether BK channel agonists rescue abnormal lysosomal storage in LSDs. In this study, we assessed the effect of BK agonist, NS1619 and NS11021 in a number of LSDs including NPC1, mild cases of mucolipidosis type IV (ML4) (TRPML1-F408∆), Niemann-Pick type A (NPA) and Fabry disease. We found that TRPML1-mediated Ca2+ release was compromised in these LSDs. BK activation corrected the impaired Ca2+ release in these LSDs and successfully rescued the abnormal lysosomal storage of these diseases by promoting TRPML1-mediated lysosomal exocytosis. Our study suggests that BK channel activation stimulates the TRPML1-BK positive reinforcing loop to correct abnormal lysosomal storage in LSDs. Drugs targeting BK channel represent a potential therapeutic approach for LSDs.

No MeSH data available.


Related in: MedlinePlus