NIBP (NIK-and-IKK2-binding protein; also known as TRAPPC9), is an important mediator of NFκB signaling and protein transport/trafficking, both of which play key roles in many physiological processes and pathological conditions. Recently, human NIBP deficiency has been linked to a novel autosomal recessive intellectual disability syndrome, NIBP Syndrome. Patients with NIBP Syndrome exhibit various symptoms including intellectual disability, developmental delays, facial dysmorphia, microcephaly, brain abnormalities, and obesity. However, the pathogenic mechanisms underlying NIBP syndrome is still unclear. In order to elucidate the mechanistic pathways impacted by NIBP deficiency, we focused on two major aspects of this disorder: neuropathological dysfunctions and spontaneous obesity. Our major hypothesis is that NIBP deficiency causes defective neural induction and impaired neuronal differentiation and causes impaired energy homeostasis in the hypothalamus.In the first part of this study, we focused on the role of NIBP in neural induction and neurogenesis, and generated microglia-containing cerebral organoids (MCOs) and neural stem/progenitor cells (NS/PCs) from NIBP Syndrome patient-derived induced pluripotent stem cells (iPSCs). Our results show that NIBP patient-derived MCOs and NS/PCs have a distinct phenotype from healthy subjects, with MCOs displaying abnormal morphology after neural induction and NS/PCs having impaired neuronal lineage differentiation. Patient MCOs have reduced numbers of NS/PCs during early stages of development, and form fewer neural rosettes during maturation. Additionally, the laminar structures present in patient MCOs are thinner and less intricate. Bulk RNAseq analysis highlights several dysregulated pathways in patient MCOs, including many genes related to protein transport/trafficking, neuritogenesis, and synaptogenesis.
The second half of this study characterized novel mouse models of Nibp deficiency, with a focus on elucidating mechanisms related to obesity and energy homeostasis. Global knockout mice (Nibp-/-) recapitulated most phenotypical characteristics with NIBP Syndrome patients, including neurogenic deficits, neurocognitive impairments, and spontaneous obesity. As mice do not develop obesity without the introduction of a high fat diet in general, this spontaneous obesity under normal chow diet is an exceptionally interesting phenotype, highlighting an important anti-obesity role of NIBP under physiological conditions. Further DEXA (dual-energy X-ray absorptiometry) and metabolic characterization of global Nibp-/- mice demonstrated that they have increased fat mass, impaired glucose and insulin tolerance, and increased food intake in addition to increased body weight. Indirect calorimetry using Comprehensive Lab Animal Monitoring System (CLAMS) metabolic cages showed Nibp-/- mice had increased respiratory exchange ratio (RER) as well as reduced locomotor activity. Finally, whole body histopathological analysis showed no apparent histopathologic abnormalities in fat, liver, pancreas, intestine, kidney, heart, and spleen tissues in Nibp-/- mice, indicating that these tissues/organs may not be directly impaired, at least at a gross level, and therefore the obesity is occurring because of other factors.
Given the hypothalamus is the master regulator of feeding behavior and energy expenditure, we addressed whether hypothalamic NIBP knockout contributes to the obese phenotype. Most interestingly, targeted knockout of Nibp in the arcuate nucleus of floxed Nibp mice via AAV-DJ8-Cre stereotactic injection resulted in spontaneous obesity similar to the global Nibp-/- mice, indicating a key role for hypothalamic NIBP signaling in food intake and energy homeostasis. To elucidate the cellular mechanisms that may be involved, we generated AgRP and POMC-specific neuronal knockout mice. However, these mice showed no significant differences in food intake and body weight from wildtype littermates during longitudinal tracking studies. Indirect calorimetry showed increased RER in both AgRP and POMC knockout mice, as well as increased food intake, locomotor activity, and energy expenditure in POMC knockout mice. Therefore, this data suggests that while hypothalamic NIBP plays an important role in energy homeostasis, it likely involves additional or separate cell types than AGRP and/or POMC neurons.
In summary, the studies conducted provide evidence that NIBP plays a significant role in neurodevelopment related to neural induction and neuronal differentiation and hypothalamic NIBP is important for maintaining energy homeostasis. / Biomedical Sciences
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/8902 |
| Date | January 2023 |
| Creators | Bodnar, Brittany, 0000-0003-0467-5219 |
| Contributors | Hu, Wenhui, Barbe, Mary F., Kim, Seonhee, Wang, Hong, 1956 September 19-, Wu, Sheng, Bethea, John R. |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 170 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/8866, Theses and Dissertations |
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