Outcomes for maximal bilateral lateral rectus recession in large-angle exotropia.

BACKGROUND: Surgical treatment for large-angle exotropia can be challenging. The aim of this study was to evaluate short-term surgical outcomes of patients with large-angle exotropia (≥50Δ) undergoing maximal bilateral lateral rectus muscle recession of 10 mm. METHODS: This was a retrospective study of consecutive patients at our institution who underwent maximal bilateral lateral rectus muscle recession for exodeviation ≥50Δ from January 1, 2008, to July 22, 2022. We subdivided the cohort into large-angle exotropia (largest amount of exodeviation at near and/or distance ≥50Δ and <65Δ) and very large-angle exotropia (largest exodeviation ≥65Δ). Patients with a history of prior eye muscle surgery, neurologic deficits, and three- or four-muscle surgery were excluded. RESULTS: A total of 22 patients were included. Mean preoperative exodeviation at distance was 51.9Δ in the large-angle group and 67.5Δ in the very-large-angle group (P = 0.001). Outcomes for the large-angle and very-large angle groups were, respectively, as follows: mean follow-up, 31.1 weeks and 11.8 weeks (P = 0.97); success, 75.0% and 16.7% (P = 0.02); undercorrection rates, 18.7% and 83.3% (P = 0.01); and mean postoperative exodeviation at distance, 3.7Δ ± 6.3Δ and 28.0Δ ± 13.5Δ (P = 0.001). CONCLUSIONS: Our study identified good surgical outcomes (75%) with maximal bilateral lateral rectus muscle recession of 10 mm in treating patients with large-angle exotropia between 50Δ and <65Δ. Other surgical techniques such as recession-resection and three- or four-muscle surgery may result in better outcomes when treating patients with exotropia ≥65Δ.

Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acids.

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We find that ALT2 is overexpressed in the liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) is downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver is mediated by activating transcription factor 4, an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuates incorporation of 13C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver has no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviates hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

Multiple antisense oligonucleotides targeted against monoacylglycerol acyltransferase 1 (Mogat1) improve glucose metabolism independently of Mogat1.

OBJECTIVE: Monoacylglycerol acyltransferase (MGAT) enzymes catalyze the synthesis of diacylglycerol from monoacylglycerol. Previous work has suggested the importance of MGAT activity in the development of obesity-related hepatic insulin resistance. Indeed, antisense oligonucleotide (ASO)-mediated knockdown of Mogat1 mRNA, which encodes MGAT1, reduced hepatic MGAT activity and improved glucose tolerance and insulin resistance in high-fat diet (HFD)-fed mice. However, recent work has suggested that some ASOs may have off-target effects on body weight and metabolic parameters via activation of the interferon alpha/beta receptor 1 (IFNAR-1) pathway. METHODS: Mice with whole-body Mogat1 knockout or a floxed allele for Mogat1 to allow for liver-specific Mogat1-knockout (by either a liver-specific transgenic or adeno-associated virus-driven Cre recombinase) were generated. These mice were placed on an HFD, and glucose metabolism and insulin sensitivity were assessed after 16 weeks on diet. In some experiments, mice were treated with control scramble or Mogat1 ASOs in the presence or absence of IFNAR-1 neutralizing antibody. RESULTS: Genetic deletion of hepatic Mogat1, either acutely or chronically, did not improve hepatic steatosis, glucose tolerance, or insulin sensitivity in HFD-fed mice. Furthermore, constitutive Mogat1 knockout in all tissues actually exacerbated HFD-induced obesity, insulin sensitivity, and glucose intolerance on an HFD. Despite markedly reduced Mogat1 expression, liver MGAT activity was unaffected in all knockout mouse models. Mogat1 overexpression in hepatocytes increased liver MGAT activity and TAG content in low-fat-fed mice but did not cause insulin resistance. Multiple Mogat1 ASO sequences improved glucose tolerance in both wild-type and Mogat1 null mice, suggesting an off-target effect. Hepatic IFNAR-1 signaling was activated by multiple Mogat1 ASOs, but its blockade did not prevent the effects of either Mogat1 ASO on glucose homeostasis. CONCLUSION: These results indicate that genetic loss of Mogat1 does not affect hepatic MGAT activity or metabolic homeostasis on HFD and show that multiple Mogat1 ASOs improve glucose metabolism through effects independent of targeting Mogat1 or activation of IFNAR-1 signaling.

Growth Factor Independence 1B-Mediated Transcriptional Repression and Lineage Allocation Require Lysine-Specific Demethylase 1-Dependent Recruitment of the BHC Complex.

Growth factor independence 1B (GFI1B) coordinates assembly of transcriptional repressor complexes comprised of corepressors and histone-modifying enzymes to control gene expression programs governing lineage allocation in hematopoiesis. Enforced expression of GFI1B in K562 erythroleukemia cells favors erythroid over megakaryocytic differentiation, providing a platform to define molecular determinants of binary fate decisions triggered by GFI1B. We deployed proteome-wide proximity labeling to identify factors whose inclusion in GFI1B complexes depends upon GFI1B's obligate effector, lysine-specific demethylase 1 (LSD1). We show that GFI1B preferentially recruits core and putative elements of the BRAF-histone deacetylase (HDAC) (BHC) chromatin-remodeling complex (LSD1, RCOR1, HMG20A, HMG20B, HDAC1, HDAC2, PHF21A, GSE1, ZMYM2, and ZNF217) in an LSD1-dependent manner to control acquisition of erythroid traits by K562 cells. Among these elements, depletion of both HMG20A and HMG20B or of GSE1 blocks GFI1B-mediated erythroid differentiation, phenocopying impaired differentiation brought on by LSD1 depletion or disruption of GFI1B-LSD1 binding. These findings demonstrate the central role of the GFI1B-LSD1 interaction as a determinant of BHC complex recruitment to enable cell fate decisions driven by GFI1B.

GFI1 functions in transcriptional control and cell fate determination require SNAG domain methylation to recruit LSD1.

Proper hematopoietic cell fate decisions require co-ordinated functions of transcription factors, their associated co-regulators, and histone-modifying enzymes. Growth factor independence 1 (GFI1) is a zinc finger transcriptional repressor and master regulator of normal and malignant hematopoiesis. While several GFI1-interacting proteins have been described, how GFI1 leverages these relationships to carry out transcriptional repression remains unclear. Here, we describe a functional axis involving GFI1, SMYD2, and LSD1 that is a critical contributor to GFI1-mediated transcriptional repression. SMYD2 methylates lysine-8 (K8) within a -(8)KSKK(11)- motif embedded in the GFI1 SNAG domain. Methylation-defective GFI1 SNAG domain lacks repressor function due to failure of LSD1 recruitment and persistence of promoter H3K4 di-methyl marks. Methylation-defective GFI1 also fails to complement GFI1 depletion phenotypes in developing zebrafish and lacks pro-growth and survival functions in lymphoid leukemia cells. Our data show a discrete methylation event in the GFI1 SNAG domain that facilitates recruitment of LSD1 to enable transcriptional repression and co-ordinate control of hematopoietic cell fate in both normal and malignant settings.

SUMOylation Regulates Growth Factor Independence 1 in Transcriptional Control and Hematopoiesis.

Cell fate specification requires precise coordination of transcription factors and their regulators to achieve fidelity and flexibility in lineage allocation. The transcriptional repressor growth factor independence 1 (GFI1) is comprised of conserved Snail/Slug/Gfi1 (SNAG) and zinc finger motifs separated by a linker region poorly conserved with GFI1B, its closest homolog. Moreover, GFI1 and GFI1B coordinate distinct developmental fates in hematopoiesis, suggesting that their functional differences may derive from structures within their linkers. We show a binding interface between the GFI1 linker and the SP-RING domain of PIAS3, an E3-SUMO (small ubiquitin-related modifier) ligase. The PIAS3 binding region in GFI1 contains a conserved type I SUMOylation consensus element, centered on lysine-239 (K239). In silico prediction algorithms identify K239 as the only high-probability site for SUMO modification. We show that GFI1 is modified by SUMO at K239. SUMOylation-resistant derivatives of GFI1 fail to complement Gfi1 depletion phenotypes in zebrafish primitive erythropoiesis and granulocytic differentiation in cultured human cells. LSD1/CoREST recruitment and MYC repression by GFI1 are profoundly impaired for SUMOylation-resistant GFI1 derivatives, while enforced expression of MYC blocks granulocytic differentiation. These findings suggest that SUMOylation within the GFI1 linker favors LSD1/CoREST recruitment and MYC repression to govern hematopoietic differentiation.