TRPML1 activation may boost Pompe ERT effects in new cell study
Experimental compounds improved enzyme uptake, processing in fibroblasts
Written by |
Activating a protein called TRPML1 with two experimental drugs improved the effects of enzyme replacement therapy (ERT) in cells derived from people with Pompe disease, a new study shows.
Boosting TRPML1 increased the amount and cell-surface availability of M6PR, a receptor that acts as a “docking station” to capture the infused ERT enzyme and help guide it into cells.
TRPML1 strategy may help enzyme therapy reach cells
“These data provide [cell-based] proof-of-concept evidence supporting the combination of ERT with pharmacological manipulation of secondarily altered M6PR distribution as a strategy to obtain better exposure of cells to therapeutic enzymes,” the researchers wrote.
The study, “TRPML1 agonists synergize with enzyme replacement therapy in fibroblasts from Pompe disease patients,” was published in the Journal of Translational Medicine.
Pompe disease is caused by a deficiency in acid alpha-glucosidase (GAA), the enzyme responsible for breaking down glycogen, a form of stored sugar, inside lysosomes, the cell’s recycling centers. Without sufficient GAA activity, glycogen accumulates inside lysosomes and damages cells, particularly in muscle tissue.
ERT is the current standard treatment for Pompe, which involves regular infusions of a lab-made version of the GAA enzyme (rhGAA). However, disease progression can resume in some patients after a few years of therapy, and some muscles appear resistant to treatment.
One factor that can limit ERT’s effectiveness is a protein called M6PR, a receptor that helps cells take up the infused enzyme and guide it into lysosomes. Previous research has shown that in Pompe disease cells, the total amount of M6PR and its cell-surface availability are reduced compared with healthy cells.
TRPML1 is a channel protein located in the lysosome membrane. It’s known to have several functions, including promoting the formation of new lysosomes and enhancing the movement of vesicles, or small transport packages, and membranes within the cell.
Given TRPML1’s functions, scientists in Italy explored whether activating it might help improve M6PR distribution and availability at the cell surface and improve how well ERT works.
Compounds boosted M6PR availability at cell surface
The team tested two TRPML1-activating compounds, WR54-006 and WR7-003, in fibroblasts, the most common cells in connective tissue, derived from six Pompe patients with different genetic mutations and disease severities.
As expected, treating fibroblasts with WR54-006 or WR7-003 increased TRPML1 expression. In tested Pompe fibroblasts, both compounds also improved markers of autophagy, the cell’s recycling process, and reduced oxidative stress, a type of cellular damage caused by reactive oxygen molecules.
At the same time, treatment with WR54-006 increased M6PR levels at the cell surface by 48%, and treatment with WR7-003 increased them by 29%, compared with untreated Pompe cells. Also, M6PR appeared scattered in untreated fibroblasts, whereas in cells treated with either compound, M6PR showed a more organized pattern, similar to that observed in healthy control cells.
Pompe fibroblasts were then pretreated with the TRPML1 activators and exposed to recombinant human GAA, the same type of enzyme used in Myozyme (alglucosidase alfa; marketed as Lumizyme in the U.S.), an ERT approved in the U.S. for all types of Pompe disease.
GAA enzyme activity was enhanced in all six cell lines tested. The mean GAA activity increased 2.05 times for WR54-006 and 2.6 times for WR7-003 compared with the ERT enzyme alone. When a TRPML1 inhibitor was added, this enhancement was abolished, confirming that the effect was mediated by TRPML1 activation, the team noted.
ERT enzyme uptake, processing improved in Pompe cells
Lastly, the team examined what happens to the ERT enzyme after it enters cells. The infused enzyme starts as a large precursor protein that is processed into smaller, active forms during lysosomal trafficking, allowing it to become fully functional.
In two Pompe cell lines co-treated with the ERT enzyme and the TRPML1 activators, both the amount of enzyme taken up by cells and its processing into these mature active forms were significantly increased.
When the researchers examined whether the ERT enzyme reached lysosomes in three Pompe cell lines, they found that cells treated with the ERT enzyme alone showed poor localization. In contrast, cells pretreated with either WR54-006 or WR7-003 showed significant improvements in the localization of the ERT enzyme with lysosomes.
“Our data provide the [basis] for pharmacological manipulation of secondarily altered cellular pathways as a strategy to obtain better exposure of tissues to therapeutic enzymes and, possibly, better [outcomes for] patients,” the researchers wrote.
Leave a comment
Fill in the required fields to post. Your email address will not be published.