Evaluation of the impact of the 2021 revised Neurofibromatosis type 1 diagnostic criteria on time to diagnosis.

Neurofibromatosis type 1 (NF1) has historically been diagnosed clinically based on the NIH Consensus Conference diagnostic criteria. The molecular and clinical knowledge of NF1 has subsequently improved, and an international group of experts published revised diagnostic criteria in 2021, incorporating new diagnostic criteria such as pathogenic variants in NF1. This study aimed to investigate the impact of these new diagnostic criteria on time to diagnosis (TTD) of NF1. A retrospective chart review of individuals evaluated for a diagnosis of NF1 at the Medical Genetics Clinic at Stanford Children's Health was performed. The TTD was determined by calculating the days between their first visit with a medical geneticist for NF1 and the date they would have received a diagnosis based on the previous NF1 diagnostic criteria and the 2021 updated diagnostic criteria. The revised diagnostic criteria for NF1 decreased TTD. The mean difference in TTD was 113 days shorter for the new criteria (p-value = 1.306x-05 ). This study highlights that the revised 2021 NF1 diagnostic criteria can decrease the TTD. The addition of a heterozygous pathogenic variant in NF1 as a criterion was the change that decreased TTD.

PPARγ is a nexus controlling alternative activation of macrophages via glutamine metabolism.

The nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) is known to regulate lipid metabolism in many tissues, including macrophages. Here we report that peritoneal macrophage respiration is enhanced by rosiglitazone, an activating PPARγ ligand, in a PPARγ-dependent manner. Moreover, PPARγ is required for macrophage respiration even in the absence of exogenous ligand. Unexpectedly, the absence of PPARγ dramatically affects the oxidation of glutamine. Both glutamine and PPARγ have been implicated in alternative activation (AA) of macrophages, and PPARγ was required for interleukin 4 (IL4)-dependent gene expression and stimulation of macrophage respiration. Indeed, unstimulated macrophages lacking PPARγ contained elevated levels of the inflammation-associated metabolite itaconate and express a proinflammatory transcriptome that, remarkably, phenocopied that of macrophages depleted of glutamine. Thus, PPARγ functions as a checkpoint, guarding against inflammation, and is permissive for AA by facilitating glutamine metabolism. However, PPARγ expression is itself markedly increased by IL4. This suggests that PPARγ functions at the center of a feed-forward loop that is central to AA of macrophages.

Distinct macrophage populations direct inflammatory versus physiological changes in adipose tissue.

Obesity is characterized by an accumulation of macrophages in adipose, some of which form distinct crown-like structures (CLS) around fat cells. While multiple discrete adipose tissue macrophage (ATM) subsets are thought to exist, their respective effects on adipose tissue, and the transcriptional mechanisms that underlie the functional differences between ATM subsets, are not well understood. We report that obese fat tissue of mice and humans contain multiple distinct populations of ATMs with unique tissue distributions, transcriptomes, chromatin landscapes, and functions. Mouse Ly6c ATMs reside outside of CLS and are adipogenic, while CD9 ATMs reside within CLS, are lipid-laden, and are proinflammatory. Adoptive transfer of Ly6c ATMs into lean mice activates gene programs typical of normal adipocyte physiology. By contrast, adoptive transfer of CD9 ATMs drives gene expression that is characteristic of obesity. Importantly, human adipose tissue contains similar ATM populations, including lipid-laden CD9 ATMs that increase with body mass. These results provide a higher resolution of the cellular and functional heterogeneity within ATMs and provide a framework within which to develop new immune-directed therapies for the treatment of obesity and related sequela.

An HDAC3-PROX1 corepressor module acts on HNF4α to control hepatic triglycerides.

The histone deacetylase HDAC3 is a critical mediator of hepatic lipid metabolism, and liver-specific deletion of HDAC3 leads to fatty liver. To elucidate the underlying mechanism, here we report a method of cross-linking followed by mass spectrometry to define a high-confidence HDAC3 interactome in vivo that includes the canonical NCoR-HDAC3 complex as well as Prospero-related homeobox 1 protein (PROX1). HDAC3 and PROX1 co-localize extensively on the mouse liver genome, and are co-recruited by hepatocyte nuclear factor 4α (HNF4α). The HDAC3-PROX1 module controls the expression of a gene program regulating lipid homeostasis, and hepatic-specific ablation of either component increases triglyceride content in liver. These findings underscore the importance of specific combinations of transcription factors and coregulators in the fine tuning of organismal metabolism.HDAC3 is a critical mediator of hepatic lipid metabolism and its loss leads to fatty liver. Here, the authors characterize the liver HDAC3 interactome in vivo, provide evidence that HDAC3 interacts with PROX1, and show that HDAC3 and PROX1 control expression of genes regulating lipid homeostasis.

Deletion of histone deacetylase 3 in adult beta cells improves glucose tolerance via increased insulin secretion.

OBJECTIVE: Histone deacetylases are epigenetic regulators known to control gene transcription in various tissues. A member of this family, histone deacetylase 3 (HDAC3), has been shown to regulate metabolic genes. Cell culture studies with HDAC-specific inhibitors and siRNA suggest that HDAC3 plays a role in pancreatic ß-cell function, but a recent genetic study in mice has been contradictory. Here we address the functional role of HDAC3 in ß-cells of adult mice. METHODS: An HDAC3 ß-cell specific knockout was generated in adult MIP-CreERT transgenic mice using the Cre-loxP system. Induction of HDAC3 deletion was initiated at 8 weeks of age with administration of tamoxifen in corn oil (2 mg/day for 5 days). Mice were assayed for glucose tolerance, glucose-stimulated insulin secretion, and islet function 2 weeks after induction of the knockout. Transcriptional functions of HDAC3 were assessed by ChIP-seq as well as RNA-seq comparing control and ß-cell knockout islets. RESULTS: HDAC3 ß-cell specific knockout (HDAC3ßKO) did not increase total pancreatic insulin content or ß-cell mass. However, HDAC3ßKO mice demonstrated markedly improved glucose tolerance. This improved glucose metabolism coincided with increased basal and glucose-stimulated insulin secretion in vivo as well as in isolated islets. Cistromic and transcriptomic analyses of pancreatic islets revealed that HDAC3 regulates multiple genes that contribute to glucose-stimulated insulin secretion. CONCLUSIONS: HDAC3 plays an important role in regulating insulin secretion in vivo, and therapeutic intervention may improve glucose homeostasis.