MEKT1, a type of therapy called a PPAR-γ agonist, acts to reduce levels of the adrenocorticotropic hormone and could be a potential new therapy for Cushing’s disease, according to researchers.
Their study, “Inhibitory Effects of a Novel PPAR-γ Agonist MEKT1 on Pomc Expression/ACTH Secretion in AtT20 Cells,” was published in the journal PPAR Research.
Cushing’s disease is caused by a tumor in the pituitary gland — generally a type of tumor called an adenoma that produces high levels of adrenocorticotropic hormone (ACTH).
ACTH causes the adrenal glands to make too much cortisol, leading to the classic symptoms associated with Cushing’s disease.
PPAR-gamma (PPAR-γ) is a transcription factor protein (meaning it regulates the levels of certain genes by acting through other proteins), and is seen in high levels in the normal human pituitary and in ACTH-secreting pituitary adenomas.
The Pomc gene is a precursor molecule to ACTH. While it is known that PPAR-γ plays a role in regulating Pomc levels, its mechanism has not yet been clarified in pituitary cells.
PPAR-γ agonists — agents that activate PPAR-γ — include the medications rosiglitazone and pioglitazone, both of which are used to treat type 2 idabetes. Some studies have shown that rosiglitazone and pioglitazone have an effect on Pomc suppression, which would lead to lower levels of ACTH and help treat patients with Cushing’s disease.
However, the benefits of PPAR-γ agonists in the treatment of Cushing’s disease are still controversial.
Researchers examined the effects of a new PPAR-γ agonist, MEKT1, on Pomc levels and ACTH secretion using a mouse pituitary tumor-derived cell line called AtT20 cells. They also compared its effects with the well-established PPAR-γ agonists rosiglitazone and pioglitazone.
AtT20 cells were treated with either MEKT1, rosiglitazone, or pioglitazone at various concentrations ranging from 1 nM to 10 μM (micrometers) for 24 hours.
Results showed that 10 μM of MEKT1 significantly inhibited Pomc gene levels compared to rosiglitazone and pioglitazone. Additionally, ACTH secretion from AtT20 cells was also significantly inhibited by the agonist.
To see if it worked to decrease Pomc levels by acting specifically on PPAR-γ, researchers eliminated the PPAR-γ protein using a technique called siRNA knockdown. In this case, the effects of MEKT1 on Pomc levels were significantly halted.
It is known that other proteins, such as Nur77, Nurr1, and Tpit activate Pomc levels by binding to the promoter region of Pomc — the area of the gene responsible for activating gene levels.
To determine whether these proteins could be targeted by MEKT1, researchers also looked at levels of Nur77, Nurr1, and Tpit. The PPAR-γ agonist was found to significantly suppress the levels of the three genes that encode these proteins.
“Although clinical trials of MEKT1 are needed to determine its drug efficacy in the future, it can be speculated that MEKT1 is much more effective than the previously recognized PPAR-γ agonists rosiglitazone, and pioglitazone for the suppression of Pomc expression/ACTH secretion from our in vitro [laboratory] research,” they added.
Results from this study suggest MEKT1 could be a potential new therapy for the treatment of Cushing’s disease.
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