Calcitriol Reverses the Down-Regulation Pattern of Tuberous Sclerosis Complex Genes in an In Vitro Calcification Model

Ca2+/Calmodulin induces translocation of membrane-associated TSC2 to the nucleus where it suppresses CYP24A1 expression

Tuberous sclerosis complex 2 (TSC2) is a tumor-suppressor protein. A loss of TSC2 function induces hyperactivation of mechanistic target of rapamycin (mTOR). The C-terminal region of TSC2 contains a calmodulin (CaM) binding region and the CaM-TSC2 interaction contributes to proper mTOR activity. However, other downstream signaling pathways/effectors activated by the CaM-TSC2 complex have not been fully elucidated. In this study, we found that activation of Ca2+/CaM signaling resulted in the translocation of membrane-associated TSC2 to the nucleus and suppressed the transcriptional activity of the vitamin D receptor (VDR). TSC2 was released from the membrane in an activated CaM-dependent state in rat brain and HeLa cells. It subsequently formed a transcriptional complex to partially suppress the transcription of CYP24A1, a well-known VDR target gene. These data suggest, in part, that TSC2 attenuates VDR-associated transcriptional regulation via Ca2+/CaM signaling.

The efficacy and safety of topical rapamycin-calcitriol for facial angiofibromas in patients with tuberous sclerosis complex: a prospective, double-blind, randomized clinical trial

BACKGROUND

The efficacy of topical rapamycin is well documented for tuberous sclerosis complex (TSC)-related facial angiofibromas (FAs). Calcitriol has been shown to lessen skin fibrosis and may be therapeutically beneficial to FAs.

OBJECTIVES

To evaluate whether topical rapamycin-calcitriol combination is an effective and safe treatment for TSC-related FAs.

METHODS

Fifty-two patients with TSC with FAs were enrolled in this prospective study including three 12-week periods. In period 1, either topical rapamycin 0·1% or calcitriol 0·0003% single-agent therapy vs. their combination was applied in a double-blind, left-right-randomized, split-face comparison. The primary outcome was the reduction of modified Facial Angiofibroma Severity Index (mFASI) at week 12. In period 2, the patients were reassigned to use on both cheeks the ointment that resulted in the better primary outcome in period 1. The treatment was discontinued in period 3 (week 25-36) and a follow-up mFASI was scored to evaluate the degree of recurrence.

RESULTS

The mean changes in mFASI at week 12 compared with baseline were -0·92, -0·44 and -1·09 for rapamycin (P ≤ 0·001), calcitriol (P = 0·039) and rapamycin-calcitriol combination (P ≤ 0·001), respectively. Although rapamycin-calcitriol combination and rapamycin had similar statistically significant decreases of mFASI at week 12, rapamycin-calcitriol combination resulted in faster improvement in erythema, greater reduction of papule elevation and longer durability after discontinuing treatment than rapamycin alone. The treatments were well tolerated.

CONCLUSIONS

This randomized clinical trial demonstrates that topical rapamycin-calcitriol combination therapy is an effective and safe regimen for TSC-related FAs. What is already known about this topic? Facial angiofibromas (FAs) cause substantial psychological distress in individuals with tuberous sclerosis complex (TSC), but invasive procedural treatments are not applicable to all patients. Topical rapamycin has been demonstrated as an effective and safe treatment regimen for TSC-related FAs. What does this study add? Compared with baseline (day 0), both topical rapamycin 0·1% and rapamycin 0·1%-calcitriol 0·0003% combination ointment achieved statistically significant reductions in modified Facial Angiofibroma Severity Index at week 12. Compared with rapamycin alone, extended use of the rapamycin-calcitriol combination regimen until week 24 showed more effectiveness in decreasing papule elevation and could maintain a longer therapeutic effect after treatment discontinuation. Linked Comment: Lee. Br J Dermatol 2020; 183:604-606.