Maternal Metabolic Syndrome Programs Mitochondrial Dysfunction via Germline Changes across Three Generations

Maternal obesity impairs offspring health, but the responsible mechanisms are not fully established. To address this question, we fed female mice a high-fat/high-sugar diet from before conception until weaning and then followed the outcomes in the next three generations of offspring, all fed a control diet. We observed that female offspring born to obese mothers had impaired peripheral insulin signaling that was associated with mitochondrial dysfunction and altered mitochondrial dynamic and complex proteins in skeletal muscle. This mitochondrial phenotype persisted through the female germline and was passed down to the second and third generations. Our results indicate that maternal programming of metabolic disease can be passed through the female germline and that the transfer of aberrant oocyte mitochondria to subsequent generations may contribute to the increased risk for developing insulin resistance.

NF1 mutation drives neuronal activity-dependent initiation of optic glioma

Neurons have recently emerged as essential cellular constituents of the tumour microenvironment, and their activity has been shown to increase the growth of a diverse number of solid tumours¹. Although the role of neurons in tumour progression has previously been demonstrated², the importance of neuronal activity to tumour initiation is less clear-particularly in the setting of cancer predisposition syndromes. Fifteen per cent of individuals with the neurofibromatosis 1 (NF1) cancer predisposition syndrome (in which tumours arise in close association with nerves) develop low-grade neoplasms of the optic pathway (known as optic pathway gliomas (OPGs)) during early childhood^3,4, raising  the possibility that postnatal light-induced activity of the optic nerve drives tumour initiation. Here we use an authenticated mouse model of OPG driven by mutations in the neurofibromatosis 1 tumour suppressor gene (Nf1)⁵ to demonstrate that stimulation of optic nerve activity increases optic glioma growth, and that decreasing visual experience via light deprivation prevents tumour formation and maintenance. We show that the initiation of Nf1-driven OPGs (Nf1-OPGs) depends on visual experience during a developmental period in which Nf1-mutant mice are susceptible to tumorigenesis. Germline Nf1 mutation in retinal neurons results in aberrantly increased shedding of neuroligin 3 (NLGN3) within the optic nerve in response to retinal neuronal activity. Moreover, genetic Nlgn3 loss or pharmacological inhibition of NLGN3 shedding blocks the formation and progression of Nf1-OPGs. Collectively, our studies establish an obligate role for neuronal activity in the development of some types of brain tumours, elucidate a therapeutic strategy to reduce OPG incidence or mitigate tumour progression, and underscore the role of Nf1mutation-mediated dysregulation of neuronal signalling pathways in mouse models of the NF1 cancer predisposition syndrome.

Obesity-exposed oocytes accumulate and transmit damaged mitochondria due to an inability to activate mitophagy

Mitochondria are the most prominent organelle in the oocyte. Somatic cells maintain a healthy population of mitochondria by degrading damaged mitochondria via mitophagy, a specialized autophagy pathway. However, evidence from previous work investigating the more general macroautophagy pathway in oocytes suggests that mitophagy may not be active in the oocyte. This would leave the vast numbers of mitochondria - poised to be inherited by the offspring - vulnerable to damage. Here we test the hypothesis that inactive mitophagy in the oocyte underlies maternal transmission of dysfunctional mitochondria. To determine whether oocytes can complete mitophagy, we used either CCCP or AntimycinA to depolarize mitochondria and trigger mitophagy. After depolarization, we did not detect co-localization of mitochondria with autophagosomes and mitochondrial DNA copy number remained unchanged, indicating the non-functional mitochondrial population was not removed. To investigate the impact of an absence of mitophagy in oocytes with damaged mitochondria on offspring mitochondrial function, we utilized in vitro fertilization of high fat high sugar (HF/HS)-exposed oocytes, which have lower mitochondrial membrane potential and damaged mitochondria. Here, we demonstrate that blastocysts generated from HF/HS oocytes have decreased mitochondrial membrane potential, lower metabolites involved in ATP generation, and accumulation of PINK1, a mitophagy marker protein. This mitochondrial phenotype in the blastocyst mirrors the phenotype we show in HF/HS exposed oocytes. Taken together, these data suggest that the mechanisms governing oocyte mitophagy are fundamentally distinct from those governing somatic cell mitophagy and that the absence of mitophagy in the setting of HF/HS exposure contributes to the oocyte-to-blastocyst transmission of dysfunctional mitochondria.

A maternal high-fat, high-sucrose diet induces transgenerational cardiac mitochondrial dysfunction independently of maternal mitochondrial inheritance

Maternal obesity is correlated with cardiovascular disease in offspring, with a 1.3-fold increase in events observed in offspring of obese women. We have observed that obesity-exposed oocytes demonstrate impaired mitophagy and transmit damaged mitochondria to the offspring. Accordingly, we hypothesized that maternal obesity induces cardiac mitochondrial dysfunction in the offspring via transgenerational inheritance of abnormal oocyte mitochondria. We mated female mice fed a high-fat/high-sucrose (HFS) diet (or chow) with chow-fed males and assessed cardiac structure and function in their descendants that were chow fed in each generation. All F1 to F3 descendants bred via the female in each generation were nonobese and demonstrated cardiac mitochondrial abnormalities with crystal rarefaction and reduced oxygen consumption pointing to a transgenerational effect, while obese F0 dams' hearts were unaffected. Furthermore, male offspring from F1 to F3 generations and female F1 and F2 offspring developed increased left ventricular (LV) mass (vs. chow-fed controls). Increased LV mass was also observed in offspring generated by in vitro fertilization of obesity-exposed oocytes and gestation in nonobese surrogates, ruling out a gestational environment effect. Contrary to our hypothesis, male F1 also transmitted these effects to their offspring, ruling out maternal mitochondria as the primary mode of transmission. We conclude that transmission of obesity-induced effects in the oocyte nucleus rather than abnormal mitochondria underlie transgenerational inheritance of cardiac mitochondrial defects in descendants of obese females. These findings will spur exploration of epigenetic alterations in the oocyte genome as potential mechanisms whereby a family history of maternal obesity predisposes to cardiovascular disease in humans.

The SARS-CoV-2 B.1.1.529 Omicron virus causes attenuated infection and disease in mice and hamsters

Despite the development and deployment of antibody and vaccine countermeasures, rapidly-spreading SARS-CoV-2 variants with mutations at key antigenic sites in the spike protein jeopardize their efficacy. The recent emergence of B.1.1.529, the Omicron variant1,2, which has more than 30 mutations in the spike protein, has raised concerns for escape from protection by vaccines and therapeutic antibodies. A key test for potential countermeasures against B.1.1.529 is their activity in pre-clinical rodent models of respiratory tract disease. Here, using the collaborative network of the SARS-CoV-2 Assessment of Viral Evolution (SAVE) program of the National Institute of Allergy and Infectious Diseases (NIAID), we evaluated the ability of multiple B.1.1.529 Omicron isolates to cause infection and disease in immunocompetent and human ACE2 (hACE2) expressing mice and hamsters. Despite modeling and binding data suggesting that B.1.1.529 spike can bind more avidly to murine ACE2, we observed attenuation of infection in 129, C57BL/6, and BALB/c mice as compared with previous SARS-CoV-2 variants, with limited weight loss and lower viral burden in the upper and lower respiratory tracts. Although K18-hACE2 transgenic mice sustained infection in the lungs, these animals did not lose weight. In wild-type and hACE2 transgenic hamsters, lung infection, clinical disease, and pathology with B.1.1.529 also were milder compared to historical isolates or other SARS-CoV-2 variants of concern. Overall, experiments from multiple independent laboratories of the SAVE/NIAID network with several different B.1.1.529 isolates demonstrate attenuated lung disease in rodents, which parallels preliminary human clinical data.

RNA sequence analysis reveals ITGAL/CD11A as a stromal regulator of murine low-grade glioma growth

BACKGROUND

Emerging insights from numerous laboratories have revealed important roles for nonneoplastic cells in the development and progression of brain tumors. One of these nonneoplastic cellular constituents, glioma-associated microglia (GAM), represents a unique population of brain monocytes within the tumor microenvironment that have been reported to both promote and inhibit glioma proliferation. To elucidate the role of GAM in the setting of low-grade glioma (LGG), we leveraged RNA sequencing meta-analysis, genetically engineered mouse strains, and human biospecimens.

METHODS

Publicly available disease-associated microglia (DAM) RNA-seq datasets were used, followed by immunohistochemistry and RNAScope validation. CD11a-deficient mouse microglia were used for in vitro functional studies, while LGG growth in mice was assessed using anti-CD11a neutralizing antibody treatment of Neurofibromatosis type 1 (Nf1) optic glioma mice in vivo.

RESULTS

We identified Itgal/CD11a enrichment in GAM relative to other DAM populations, which was confirmed in several independently generated murine models of Nf1 optic glioma. Moreover, ITGAL/CD11A expression was similarly increased in human LGG (pilocytic astrocytoma) specimens from several different datasets, specifically in microglia from these tumors. Using CD11a-knockout mice, CD11a expression was shown to be critical for murine microglia CX3CL1 receptor (Cx3cr1) expression and CX3CL1-directed motility, as well as glioma mitogen (Ccl5) production. Consistent with an instructive role for CD11a+ microglia in stromal control of LGG growth, antibody-mediated CD11a inhibition reduced mouse Nf1 LGG growth in vivo.

CONCLUSIONS

Collectively, these findings establish ITGAL/CD11A as a critical microglia regulator of LGG biology relevant to future stroma-targeted brain tumor treatment strategies.

Excess Maternal Fructose Consumption Increases Fetal Loss and Impairs Endometrial Decidualization in Mice

The most significant increase in metabolic syndrome over the previous decade occurred in women of reproductive age, which is alarming given that metabolic syndrome is associated with reproductive problems including subfertility and early pregnancy loss. Individuals with metabolic syndrome often consume excess fructose, and several studies have concluded that excess fructose intake contributes to metabolic syndrome development. Here, we examined the effects of increased fructose consumption on pregnancy outcomes in mice. Female mice fed a high-fructose diet (HFrD) for 6 weeks developed glucose intolerance and mild fatty liver but did not develop other prominent features of metabolic syndrome such as weight gain, hyperglycemia, and hyperinsulinemia. Upon mating, HFrD-exposed mice had lower pregnancy rates and smaller litters at midgestation than chow-fed controls. To explain this phenomenon, we performed artificial decidualization experiments and found that HFrD consumption impaired decidualization. This appeared to be due to decreased circulating progesterone as exogenous progesterone administration rescued decidualization. Furthermore, HFrD intake was associated with decreased bone morphogenetic protein 2 expression and signaling, both of which were restored by exogenous progesterone. Finally, expression of forkhead box O1 and superoxide dismutase 2 [Mn] proteins were decreased in the uteri of HFrD-fed mice, suggesting that HFrD consumption promotes a prooxidative environment in the endometrium. In summary, these data suggest that excess fructose consumption impairs murine fertility by decreasing steroid hormone synthesis and promoting an adverse uterine environment.

Therapeutic and vaccine-induced cross-reactive antibodies with effector function against emerging Omicron variants

Currently circulating SARS-CoV-2 variants acquired convergent mutations at receptor-binding domain (RBD) hot spots. Their impact on viral infection, transmission, and efficacy of vaccines and therapeutics remains poorly understood. Here, we demonstrate that recently emerged BQ.1.1. and XBB.1 variants bind ACE2 with high affinity and promote membrane fusion more efficiently than earlier Omicron variants. Structures of the BQ.1.1 and XBB.1 RBDs bound to human ACE2 and S309 Fab (sotrovimab parent) explain the altered ACE2 recognition and preserved antibody binding through conformational selection. We show that sotrovimab binds avidly to all Omicron variants, promotes Fc-dependent effector functions and protects mice challenged with BQ.1.1, the variant displaying the greatest loss of neutralization. Moreover, in several donors vaccine-elicited plasma antibodies cross-react with and trigger effector functions against Omicron variants despite reduced neutralizing activity. Cross-reactive RBD-directed human memory B cells remained dominant even after two exposures to Omicron spikes, underscoring persistent immune imprinting. Our findings suggest that this previously overlooked class of cross-reactive antibodies, exemplified by S309, may contribute to protection against disease caused by emerging variants through elicitation of effector functions.

Effects of oral contraceptives on glucoregulatory responses to exercise

Some of the effects of oral contraceptives (OCs) to alter glucoregulation may be ameliorated by exercise. To test this premise, the effects of acute aerobic exercise on postprandial glucose, insulin, and C-peptide responses (area under the curve [AUC]) were measured in 8 users of low-dose estrogen and progestin OCs (OC(+)) and 10 women not using OCs (OC(-)). They completed 2 randomly ordered intervention trials: (1) aerobic exercise on 3 consecutive days with a 2.5-hour, 75-g oral glucose tolerance test (OGTT) on day 4, and (2) no exercise for 3 days prior to the OGTT (control trial). The exercise was 50 minutes of treadmill walking at 70% (.-)VO(2max). The groups were similar in age (27 +/- 3 years), waist-to-hip ratio (0.74 +/- 0.01), and cardiorespiratory fitness (32.5 +/- 1.6 mL x kg body mass(-1) x min(-1)). Fasting plasma glucose, C-peptide, and insulin levels were similar (P >.05) between groups in the control trial. In both trials, glucose(AUC) was significantly greater (13%, P <.05) in OC(+). Exercise resulted in a significant (P <.05) decrease in fasting plasma glucose and insulin, insulin(AUC), glucose(AUC) x insulin(AUC), and C-peptide(AUC) in both groups, suggesting enhanced insulin action and/or reduced pancreatic insulin secretion. Hepatic insulin extraction ([C-peptide(AUC) - insulin(AUC)())]/C-peptide(AUC)) was increased following exercise only in OC(+). Thus, insulin action was enhanced in response to exercise in young sedentary women independent of OC use. The mechanisms for the acute exercise effect on insulin action may be different in OC users compared with normally menstruating women.

LGG-50. Human induced pluripotent stem cell engineering establishes a humanized mouse platform for pediatric low-grade glioma modeling

A major obstacle to identifying improved treatments for pediatric low-grade brain tumors (gliomas) is the inability to reproducibly generate human xenografts. To surmount this barrier, we leveraged human induced pluripotent stem cell (hiPSC) engineering to generate low-grade glioma (LGG) lesions representing the two most common pediatric pilocytic astrocytoma-associated molecular alterations, NF1 loss and KIAA1549:BRAF fusion. Using hiPSCs, we identified the susceptible cells of origin for these tumors, and demonstrated that the resulting tumors retain LGG histologic features for at least 6 months in vivo. Finally, this platform enabled the successful long-term growth of patient-derived pLGGs in vivo. Taken together, these avatars establish tractable experimental humanized platforms to elucidate the pathogenesis of childhood brain tumors.

Nf1 mutation disrupts activity-dependent oligodendroglial plasticity and motor learning in mice

Neurogenetic disorders, such as neurofibromatosis type 1 (NF1), can cause cognitive and motor impairments, traditionally attributed to intrinsic neuronal defects such as disruption of synaptic function. Activity-regulated oligodendroglial plasticity also contributes to cognitive and motor functions by tuning neural circuit dynamics. However, the relevance of oligodendroglial plasticity to neurological dysfunction in NF1 is unclear. Here we explore the contribution of oligodendrocyte progenitor cells (OPCs) to pathological features of the NF1 syndrome in mice. Both male and female littermates (4-24 weeks of age) were used equally in this study. We demonstrate that mice with global or OPC-specific Nf1 heterozygosity exhibit defects in activity-dependent oligodendrogenesis and harbor focal OPC hyperdensities with disrupted homeostatic OPC territorial boundaries. These OPC hyperdensities develop in a cell-intrinsic Nf1 mutation-specific manner due to differential PI3K/AKT activation. OPC-specific Nf1 loss impairs oligodendroglial differentiation and abrogates the normal oligodendroglial response to neuronal activity, leading to impaired motor learning performance. Collectively, these findings show that Nf1 mutation delays oligodendroglial development and disrupts activity-dependent OPC function essential for normal motor learning in mice.

TAMI-69. NF1 MUTATION DRIVES NEURONAL ACTIVITY-DEPENDENT OPTIC GLIOMA INITIATION

Neurons have recently emerged as essential cellular constituents of the tumor microenvironment, where their activity increases the growth of a diverse number of solid tumors. While the role of neurons in tumor progression has been previously demonstrated, the importance of neuronal activity to tumor initiation is less clear, particularly in the setting of cancer predisposition syndromes. In the Neurofibromatosis-1 (NF1) cancer predisposition syndrome, in which tumors arise in close association with nerves, 15% of individuals develop low-grade neoplasms of the optic pathway (optic pathway gliomas [OPGs]), during early childhood, raising the intriguing possibility that postnatal light-induced optic nerve activity drives tumor initiation. Here, we employ an authenticated murine model of Nf1-OPG to demonstrate that stimulation of optic nerve activity increases optic glioma growth, while decreasing visual experience via light deprivation prevents tumor formation and maintenance. We show that Nf1-OPG initiation depends on visual experience during a developmental period susceptible to tumorigenesis. Germline Nf1 mutation in retinal neurons results in aberrantly high optic nerve neuroligin-3 (Nlgn3) shedding in response to retinal neuronal activity. Moreover, genetic Nlgn3 loss or pharmacological inhibition of Nlgn3 shedding blocks murine Nf1 optic gliomagenesis and progression. Collectively, these studies establish an obligate role for neuronal activity in the development of certain brain tumors, elucidate a therapeutic strategy to reduce OPG incidence or mitigate tumor progression, and underscore the role of Nf1 mutation-mediated dysregulation of neuronal signaling pathways in the NF1 cancer predisposition syndrome.

LGG-01. NF1 MUTATION DRIVES NEURONAL ACTIVITY-DEPENDENT OPTIC GLIOMA INITIATION

Neurons have recently emerged as essential cellular constituents of the tumor microenvironment, where their activity increases the growth of a diverse number of solid tumors. While the role of neurons in tumor progression has been previously demonstrated, the importance of neuronal activity to tumor initiation is less clear, particularly in the setting of cancer predisposition syndromes. In the Neurofibromatosis type 1 (NF1) cancer predisposition syndrome, in which tumors arise in close association with nerves, 15% of individuals develop low-grade neoplasms of the optic pathway (optic gliomas) during early childhood, raising the intriguing possibility that postnatal light-induced optic nerve activity drives tumor initiation. Here, we employ an authenticated murine model of Nf1 optic glioma to demonstrate that stimulation of optic nerve activity increases optic glioma growth, while decreasing optic nerve activity via light deprivation prevents tumor formation and maintenance. By manipulating environmental light to modulate optic pathway (retinal) neuron activity, we show that Nf1 optic glioma initiation depends on neuronal activity during a developmental period susceptible to tumorigenesis. Germline Nf1 mutation in retinal neurons results in aberrantly high optic nerve neuroligin-3 (Nlgn3) shedding in response to retinal neuronal activity. Moreover, genetic Nlgn3 loss or pharmacologic inhibition of Nlgn3 shedding blocks murine Nf1 optic gliomagenesis and progression. Collectively, these studies establish an obligate role for neuronal activity in the development of certain brain tumors, elucidate a therapeutic strategy to reduce optic glioma incidence or mitigate tumor progression, and underscore the role of Nf1 mutation-mediated dysregulation of neuronal signaling pathways in the NF1 cancer predisposition syndrome.