Iwasaki Yorihiro, Reyes Monica, Ryabets-Lienhard Anna, Gales Barbara, Linglart Agnès, Miller Danny E, Salusky Isidro B, Bastepe Murat, Jüppner Harald
Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114.
Division of Endocrinology, Metabolism & Nephrology, Tazuke Kofukai Medical Research Institute, Kitano Hospital, Osaka 5308480, Japan.
Proc Natl Acad Sci U S A. 2025 Apr 22;122(16):e2423271122. doi: 10.1073/pnas.2423271122. Epub 2025 Apr 18.
Pseudohypoparathyroidism type 1B (PHP1B) is a multihormone resistance disorder caused by aberrant methylation. Characteristic epigenetic changes at differentially methylated regions (DMRs), i.e., NESP, AS1, AS2, XL, and A/B, are associated with specific structural defects in different autosomal dominant PHP1B (AD-PHP1B) subtypes. However, mechanisms underlying abnormal methylation remain incompletely defined, largely because viable PHP1B mouse models are lacking. Using lymphoblastoid cells and induced pluripotent stem cells, we show that various methylation patterns in PHP1B reflect differential disruption of sense and antisense transcripts. In cases with broad methylation changes, loss of the maternal, sense-transcribed exon H/AS region impairs methylation of the AS1 DMR, which results in biallelic expression of an antisense transcript, , and NESP hypermethylation. In contrast, cases with normal AS1 methylation, including deletions, show monoallelic expression and normal NESP methylation. The roles of these transcripts were confirmed by a retrotransposon in intron 1, identified in an AD-PHP1B family. This insertion impaired exon H/AS transcription when located on the maternal allele, thus preventing the complete establishment of methylation at all maternal DMRs, leading to biallelic transcription. However, maternal transcription was profoundly attenuated, thus allowing only a small gain-of-methylation at NESP. Likewise, on the paternal allele, the retrotransposon attenuated transcription, thus preventing complete NESP methylation. Our findings support a model of bidirectional transcription-mediated regulation of methylation at DMRs and will help to refine systematic approaches for establishing molecular defects underlying different PHP1B subtypes.
1B型假性甲状旁腺功能减退症（PHP1B）是一种由异常甲基化引起的多激素抵抗性疾病。在差异甲基化区域（DMRs），即NESP、AS1、AS2、XL和A/B处的特征性表观遗传变化，与不同常染色体显性PHP1B（AD-PHP1B）亚型中的特定结构缺陷相关。然而，异常甲基化的潜在机制仍未完全明确，这主要是因为缺乏可行的PHP1B小鼠模型。利用淋巴母细胞和诱导多能干细胞，我们发现PHP1B中的各种甲基化模式反映了正义和反义转录本的差异破坏。在广泛甲基化变化的病例中，母本正义转录的外显子H/AS区域的缺失会损害AS1 DMR的甲基化，这会导致反义转录本的双等位基因表达以及NESP高甲基化。相比之下，AS1甲基化正常的病例，包括缺失，表现为单等位基因表达和正常的NESP甲基化。在一个AD-PHP1B家族中鉴定出的内含子1中的逆转座子证实了这些转录本的作用。当位于母本等位基因上时，这种插入会损害外显子H/AS转录，从而阻止所有母本DMR处甲基化的完全建立，导致双等位基因转录。然而，母本转录会显著减弱，因此仅允许NESP处有少量甲基化增加。同样，在父本等位基因上，逆转座子会减弱转录，从而阻止NESP的完全甲基化。我们的研究结果支持一种双向转录介导的DMR甲基化调控模型，并将有助于完善用于确定不同PHP1B亚型潜在分子缺陷的系统方法。
