A mouse model of Weaver syndrome displays overgrowth and excess osteogenesis reversible with KDM6A/6B inhibition

Minimally Humanized Ezh2 Exon-18 Mouse Cell Lines Validate Preclinical CRISPR/Cas9 Approach to Treat Weaver Syndrome

Weaver syndrome is a rare neurodevelopmental disorder that encompasses macrocephaly, tall stature, obesity, brain anomalies, intellectual disability, and increased susceptibility to cancer. This dominant monogenic disorder is caused by germline variants in enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), a key epigenetic writer. Unfortunately, there are no effective treatments for Weaver syndrome. However, preclinical results support the potential for therapeutic gains, despite the prenatal onset. Thus, for the first time, we tested whether CRISPR/Cas9 gene-editing strategies may be able to "correct" a Weaver syndrome variant at the DNA level. We initiated these preclinical studies by humanizing the region surrounding the most-common recurring patient-variant location in mouse embryonic stem cells (ESCs). Humanization ensures that DNA-binding strategies will be directly translatable to human cells and patients. We then introduced into ESCs the humanized region, but now carrying the Weaver syndrome EZH2 variant c.2035C>T p.Arg684Cys, and characterized the enzymatic properties of this missense variant. Our data showed a significant and dramatic reduction in EZH2-enzymatic activity, supporting previous cell-free studies of this variant as well as in vitro and in vivo mouse work by other teams. Intriguingly, this most-common variant does not create a complete loss-of-function, but rather is a hypomorphic allele. Together with prior reports describing hypomorphic effects of missense EZH2 variants, these results demonstrate that the etiology of Weaver syndrome does not require complete loss of EZH2 enzymatic activity. Toward therapy, we tested four CRISPR gene-editing strategies. We demonstrated that Streptococcus pyogenes Cas9 (SpCas9) showed the highest variant correction (70.5%), but unfortunately also the highest alteration of the nonvariant allele (21.1-26.2%), an important consideration for gene-editing treatment of a dominant syndrome. However, Staphylococcus aureus Cas9 (SaCas9) gave a variant correction (52.5%) that was not significantly different than SpCas9, and encouragingly the lowest alteration of the nonvariant allele (2.0%). Thus, the therapeutic strategy using the small SaCas9 enzyme, a size that allows flexibility in therapeutic delivery, was the most optimal for targeting the Weaver syndrome EZH2 variant c.2035C>T p.Arg684Cys.

Elevated levels of neutrophils with a pro-inflammatory profile in Turner syndrome across karyotypes

Turner syndrome (TS) presents with multiple karyotypes, including 45,X monosomy and variants such as isochromosomes and mosaicism, and is characterized by several co-morbidities, including metabolic conditions and autoimmunity. Here, we investigated the genomic landscapes across a range of karyotypes. We show that TS have a common autosomal methylome and transcriptome, despite distinct karyotypic variations. All TS individuals lacked the X chromosome p-arm, and XIST expression from the q-arm did not affect the autosomal transcriptome or methylome, highlighting the critical role of the missing p-arm with its pseudoautosomal region 1. Furthermore, we show increased levels of neutrophils and increased neutrophil activation. The increase in neutrophils was linked to TS clinical traits and to increased expression of the X-Y homologous gene TBL1X, suggesting a genetic basis, which may lead to neutrophil-driven inflammatory stress in TS. Identifying TS individuals with increased neutrophil activation could potentially mitigate the progression towards more severe metabolic issues.

Tricarboxylic Acid Cycle Regulation of Metabolic Program, Redox System, and Epigenetic Remodeling for Bone Health and Disease

Imbalanced osteogenic cell-mediated bone gain and osteoclastic remodeling accelerates the development of osteoporosis, which is the leading risk factor of disability in the elderly. Harmonizing the metabolic actions of bone-making cells and bone resorbing cells to the mineralized matrix network is required to maintain bone mass homeostasis. The tricarboxylic acid (TCA) cycle in mitochondria is a crucial process for cellular energy production and redox homeostasis. The canonical actions of TCA cycle enzymes and intermediates are indispensable in oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis for osteogenic differentiation and osteoclast formation. Knockout mouse models identify these enzymes' roles in bone mass and microarchitecture. In the noncanonical processes, the metabolites as a co-factor or a substrate involve epigenetic modification, including histone acetyltransferases, DNA demethylases, RNA m6A demethylases, and histone demethylases, which affect genomic stability or chromatin accessibility for cell metabolism and bone formation and resorption. The genetic manipulation of these epigenetic regulators or TCA cycle intermediate supplementation compromises age, estrogen deficiency, or inflammation-induced bone mass loss and microstructure deterioration. This review sheds light on the metabolic functions of the TCA cycle in terms of bone integrity and highlights the crosstalk of the TCA cycle and redox and epigenetic pathways in skeletal tissue metabolism and the intermediates as treatment options for delaying osteoporosis.