Younger and Rural Children are More Likely to be Hospitalized for SARS-CoV-2 Infections.

Purpose: To identify characteristics of SARS-CoV-2 infection that are associated with hospitalization in children initially evaluated in a Pediatric Emergency Department (ED). Methods: We identified cases of SARS-CoV-2 positive patients seen in the Arkansas Children's Hospital (ACH) ED or hospitalized between May 27, 2020, and April 28, 2022 using ICD-10 codes within the Pediatric Hospital Information System (PHIS) Database. We compared infection waves for differences in patient characteristics, and used logistic regressions to examine which characteristics led to a higher chance of hospitalization. Findings: We included 681 pre-Delta cases, 673 Delta cases, and 970 Omicron cases. Almost 17% of patients were admitted to the hospital. Compared to Omicron infected children, pre-Delta and Delta infected children were twice as likely to be hospitalized (OR=2.2 and 2.0, respectively; p<0.0001). Infants less than 1 year of age were >3 times as likely to be hospitalized than children ages 5-14 years regardless of wave (OR=3.42; 95%CI=2.36-4.94). Rural children were almost 3 times as likely than urban children to be hospitalized across all waves (OR=2.73; 95%CI=1.97-3.78). Finally, those with a complex condition had nearly a 15-fold increase in odds of admission (OR=14.6; 95%CI=10.6-20.0). Conclusions: Children diagnosed during the pre-Delta or Delta waves were more likely to be hospitalized than those diagnosed during the Omicron wave. Younger and rural patients were more likely to be hospitalized regardless of wave. We suspect lower vaccination rates and larger distances from medical care influenced higher hospitalization rates.

A germline point mutation in Runx1 uncouples its role in definitive hematopoiesis from differentiation.

Definitive hematopoiesis requires the master hematopoietic transcription factor Runx1, which is a frequent target of leukemia-related chromosomal translocations. Several of the translocation-generated fusion proteins retain the DNA binding activity of Runx1, but lose subnuclear targeting and associated transactivation potential. Complete loss of these functions in vivo resembles Runx1 ablation, which causes embryonic lethality. We developed a knock-in mouse that expresses full-length Runx1 with a mutation in the subnuclear targeting cofactor interaction domain, Runx1(HTY350-352AAA). Mutant mice survive to adulthood, and hematopoietic stem cell emergence appears to be unaltered. However, defects are observed in multiple differentiated hematopoietic lineages at stages where Runx1 is known to play key roles. Thus, a germline mutation in Runx1 reveals uncoupling of its functions during developmental hematopoiesis from subsequent differentiation across multiple hematopoietic lineages in the adult. These findings indicate that subnuclear targeting and cofactor interactions with Runx1 are important in many compartments throughout hematopoietic differentiation.

Dicer inactivation in osteoprogenitor cells compromises fetal survival and bone formation, while excision in differentiated osteoblasts increases bone mass in the adult mouse.

MicroRNA attenuation of protein translation has emerged as an important regulator of mesenchymal cell differentiation into the osteoblast lineage. A compelling question is the extent to which miR biogenesis is obligatory for bone formation. Here we show conditional deletion of the Dicer enzyme in osteoprogenitors by Col1a1-Cre compromised fetal survival after E14.5. A mechanism was associated with the post-commitment stage of osteoblastogenesis, demonstrated by impaired ECM mineralization and reduced expression of mature osteoblast markers during differentiation of mesenchymal cells of ex vivo deleted Dicer(c/c). In contrast, in vivo excision of Dicer by Osteocalcin-Cre in mature osteoblasts generated a viable mouse with a perinatal phenotype of delayed bone mineralization which was resolved by 1 month. However, a second phenotype of significantly increased bone mass developed by 2 months, which continued up to 8 months in long bones and vertebrae, but not calvariae. Cortical bone width and trabecular thickness in Dicer(Deltaoc/Deltaoc) was twice that of Dicer(c/c) controls. Normal cell and tissue organization was observed. Expression of osteoblast and osteoclast markers demonstrated increased coupled activity of both cell types. We propose that Dicer generated miRs are essential for two periods of bone formation, to promote osteoblast differentiation before birth, and control bone accrual in the adult.

Definitive hematopoiesis requires Runx1 C-terminal-mediated subnuclear targeting and transactivation.

Runx1 is a key hematopoietic transcription factor required for definitive hematopoiesis and is a frequent target of leukemia-related chromosomal translocations. The resulting fusion proteins, while retaining DNA binding activity, display loss of subnuclear targeting and associated transactivation functions encoded by the C-terminus of the protein. To define the precise contribution of the Runx1 C-terminus in development and leukemia, we created a knock-in mouse with a C-terminal truncation by introducing a single nucleic acid substitution in the native Runx1 locus. This mutation (Runx1(Q307X)) models genetic lesions observed in patients with leukemia and myeloproliferative disorders. The Runx1(Q307X) homozygous mouse exhibits embryonic lethality at E12.5 due to central nervous system hemorrhages and a complete lack of hematopoietic stem cell function. While able to bind DNA, Runx1(Q307X) is unable to activate target genes, resulting in deregulation of various hematopoietic markers. Thus, we demonstrate that the subnuclear targeting and transcriptional regulatory activities of the Runx1 C-terminus are critical for hematopoietic development. We propose that compromising the C-terminal functions of Runx1 is a common mechanism for the pathological consequences of a variety of somatic mutations and Runx1-related leukemic fusion proteins observed in human patients.

A Runx2 threshold for the cleidocranial dysplasia phenotype.

Cleidocranial dysplasia (CCD) in humans is an autosomal-dominant skeletal disease that results from mutations in the bone-specific transcription factor RUNX2 (CBFA1/AML3). However, distinct RUNX2 mutations in CCD do not correlate with the severity of the disease. Here we generated a new mouse model with a hypomorphic Runx2 mutant allele (Runx2(neo7)), in which only part of the transcript is processed to full-length (wild-type) Runx2 mRNA. Homozygous Runx2(neo7/neo7) mice express a reduced level of wild-type Runx2 mRNA (55-70%) and protein. This mouse model allowed us to establish the minimal requirement of functional Runx2 for normal bone development. Runx2(neo7/neo7) mice have grossly normal skeletons with no abnormalities observed in the growth plate, but do exhibit developmental defects in calvaria and clavicles that persist through post-natal growth. Clavicle defects are caused by disrupted endochondral bone formation during embryogenesis. These hypomorphic mice have altered calvarial bone volume, as observed by histology and microCT imaging, and decreased expression of osteoblast marker genes. The bone phenotype of the heterozygous mice, which have 79-84% of wild-type Runx2 mRNA, is normal. These results show there is a critical gene dosage requirement of functional Runx2 for the formation of intramembranous bone tissues during embryogenesis. A decrease to 70% of wild-type Runx2 levels results in the CCD syndrome, whereas levels >79% produce a normal skeleton. Our findings suggest that the range of bone phenotypes in CCD patients is attributable to quantitative reduction in the functional activity of RUNX2.

Synergistic inhibitory effects of gastrin and histamine receptor antagonists on Helicobacter-induced gastric cancer.

BACKGROUND & AIMS: Apart from its importance as an acid secretogogue, the role of histamine as a downstream target of gastrin has not been fully explored. Previous studies have shown that the combination of hypergastrinemia and Helicobacter infection resulted in accelerated gastric cancer in mice. We used this model to examine the role of cholecystokinin 2 (CCK2)/gastrin receptor and histamine H2-receptor signaling in the development of gastric atrophy and cancer. METHODS: Male hypergastrinemic mice (INS-GAS mice) were infected with Helicobacter felis and given the CCK2/gastrin receptor antagonist YF476 and/or the histamine H2-receptor antagonist loxtidine for 3 or 6 months. In addition, mice were treated with omeprazole alone or in combination with either YF476 or loxtidine for 3 months. RESULTS: Mice treated with YF476 or loxtidine alone showed partial suppression of both gastric acid secretion and progression to neoplasia. The combination of YF476 plus loxtidine treatment resulted in nearly complete inhibition of both parameters. YF476 and/or loxtidine treatment did not alter the overall level of H. felis colonization but did result in significant down-regulation of the growth factors regenerating gene I and amphiregulin. Loxtidine treatment, with or without YF476, induced a mild shift in T-helper cell polarization. In contrast, omeprazole treatment resulted in mild progression of gastric hyperplasia/dysplasia, which was ameliorated by the addition of YF476 or loxtidine. CONCLUSIONS: The combination of CCK2/gastrin- and histamine H2-receptor antagonists has synergistic inhibitory effects on development of gastric atrophy and cancer in H. felis/INS-GAS mice, while the proton pump inhibitor showed no such effects. These results support an important role for the gastrin-histamine axis in Helicobacter-induced gastric carcinogenesis.