Characterizing the human APOE epsilon 4 knock-in transgene in female and male rats with multimodal magnetic resonance imaging

Exploring the parity paradox: Differential effects on neuroplasticity and inflammation by APOEe4 genotype at middle age

Female sex and Apolipoprotein E (APOE) ε4 genotype are top non-modifiable risk factors for Alzheimer's disease (AD). Although female-unique experiences like parity (pregnancy and motherhood) have positive effects on neuroplasticity at middle age, previous pregnancy may also contribute to AD risk. To explore these seemingly paradoxical long-term effects of parity, we investigated the impact of parity with APOEε4 genotype by examining behavioural and neural biomarkers of brain health in middle-aged female rats. Our findings show that primiparous (parous one time) hAPOEε4 rats display increased use of a non-spatial cognitive strategy and exhibit decreased number and recruitment of new-born neurons in the ventral dentate gyrus of the hippocampus in response to spatial working memory retrieval. Furthermore, primiparity and hAPOEε4 genotype synergistically modulate inflammatory markers in the ventral hippocampus. Collectively, these findings demonstrate that previous parity in hAPOEε4 rats confers an added risk to present with reduced activity and engagement of the hippocampus as well as elevated pro-inflammatory signaling, and underscore the importance of considering female-specific factors and genotype in health research.

Neuroanatomical and functional consequences of oxytocin treatment at birth in prairie voles

Birth is a critical period for the developing brain, a time when surging hormone levels help prepare the fetal brain for the tremendous physiological changes it must accomplish upon entry into the 'extrauterine world'. A number of obstetrical conditions warrant manipulations of these hormones at the time of birth, but we know little of their possible consequences on the developing brain. One of the most notable birth signaling hormones is oxytocin, which is administered to roughly 50% of laboring women in the United States prior to / during delivery. Previously, we found evidence for behavioral, epigenetic, and neuroendocrine consequences in adult prairie vole offspring following maternal oxytocin treatment immediately prior to birth. Here, we examined the neurodevelopmental consequences in adult prairie vole offspring following maternal oxytocin treatment prior to birth. Control prairie voles and those exposed to 0.25 mg/kg oxytocin were scanned as adults using anatomical and functional MRI, with neuroanatomy and brain function analyzed as voxel-based morphometry and resting state functional connectivity, respectively. Overall, anatomical differences brought on by oxytocin treatment, while widespread, were generally small, while differences in functional connectivity, particularly among oxytocin-exposed males, were larger. Analyses of functional connectivity based in graph theory revealed that oxytocin-exposed males in particular showed markedly increased connectivity throughout the brain and across several parameters, including closeness and degree. These results are interpreted in the context of the organizational effects of oxytocin exposure in early life and these findings add to a growing literature on how the perinatal brain is sensitive to hormonal manipulations at birth.

Loss of aquaporin-4 results in glymphatic system dysfunction via brain-wide interstitial fluid stagnation

The glymphatic system is a fluid transport network of cerebrospinal fluid (CSF) entering the brain along arterial perivascular spaces, exchanging with interstitial fluid (ISF), ultimately establishing directional clearance of interstitial solutes. CSF transport is facilitated by the expression of aquaporin-4 (AQP4) water channels on the perivascular endfeet of astrocytes. Mice with genetic deletion of AQP4 (AQP4 KO) exhibit abnormalities in the brain structure and molecular water transport. Yet, no studies have systematically examined how these abnormalities in structure and water transport correlate with glymphatic function. Here, we used high-resolution 3D magnetic resonance (MR) non-contrast cisternography, diffusion-weighted MR imaging (MR-DWI) along with intravoxel-incoherent motion (IVIM) DWI, while evaluating glymphatic function using a standard dynamic contrast-enhanced MR imaging to better understand how water transport and glymphatic function is disrupted after genetic deletion of AQP4. AQP4 KO mice had larger interstitial spaces and total brain volumes resulting in higher water content and reduced CSF space volumes, despite similar CSF production rates and vascular density compared to wildtype mice. The larger interstitial fluid volume likely resulted in increased slow but not fast MR diffusion measures and coincided with reduced glymphatic influx. This markedly altered brain fluid transport in AQP4 KO mice may result from a reduction in glymphatic clearance, leading to enlargement and stagnation of fluid in the interstitial space. Overall, diffusion MR is a useful tool to evaluate glymphatic function and may serve as valuable translational biomarker to study glymphatics in human disease.

Autoregulation of Pax6 in neuronal cells is mediated by Pax6(5a), Pax6(ΔPD), SPARC, and p53

BACKGROUND

Pax6, a multifunctional protein and a transcriptional regulator is critical for optimal functioning of neuronal cells. It is known that alternatively spliced Pax6 isoforms and co-expressed interacting proteins mediate cell/tissue specific autoregulation of Pax6, however, underlying mechanism(s) are poorly understood.

METHODS AND RESULTS

We used Neuro-2a cells to explore the mechanism of autoregulation of Pax6 in neuronal cells whereas NIH/3T3 cells were used as control. We first studied the transcript expression of the three Pax6 isoforms: Pax6, Pax6(5a), and Pax6(ΔPD); and the two co-expressed Pax6-interacting partners: SPARC and p53 in normal and overexpressed conditions, through the semi-quantitative RT-PCR. Further, we used the luciferase reporter assay to study the binding and transactivation of the three Pax6 isoforms: Pax6, Pax6(5a), and Pax6(ΔPD) to their respective promoters: P0, P1, and Pα; followed by that of the two co-expressed Pax6-interacting partners: SPARC and p53 to the Pax6-P1 promoter. Expression and distribution of Pax6, Pax6(5a) and Pax6(ΔPD), their binding to Pax6-promoters (P0, P1, and Pα) and transactivation were modulated in transfected Neuro-2a cells.

CONCLUSION

Our results suggest that autoregulation of Pax6 in neuronal cells is driven by a promoter dependent mechanism which is mediated by spliced variants [Pax6(5a) and Pax6(ΔPD)] and interacting proteins (SPARC and p53) of Pax6.

Genetic Variants Associated With Resilience in Human and Animal Studies

Resilience is broadly defined as the ability to maintain or regain functioning in the face of adversity and is influenced by both environmental and genetic factors. The identification of specific genetic factors and their biological pathways underpinning resilient functioning can help in the identification of common key factors, but heterogeneities in the operationalisation of resilience have hampered advances. We conducted a systematic review of genetic variants associated with resilience to enable the identification of general resilience mechanisms. We adopted broad inclusion criteria for the definition of resilience to capture both human and animal model studies, which use a wide range of resilience definitions and measure very different outcomes. Analyzing 158 studies, we found 71 candidate genes associated with resilience. OPRM1 (Opioid receptor mu 1), NPY (neuropeptide Y), CACNA1C (calcium voltage-gated channel subunit alpha1 C), DCC (deleted in colorectal carcinoma), and FKBP5 (FKBP prolyl isomerase 5) had both animal and human variants associated with resilience, supporting the idea of shared biological pathways. Further, for OPRM1, OXTR (oxytocin receptor), CRHR1 (corticotropin-releasing hormone receptor 1), COMT (catechol-O-methyltransferase), BDNF (brain-derived neurotrophic factor), APOE (apolipoprotein E), and SLC6A4 (solute carrier family 6 member 4), the same allele was associated with resilience across divergent resilience definitions, which suggests these genes may therefore provide a starting point for further research examining commonality in resilience pathways.

Neurovascular imaging with QUTE-CE MRI in APOE4 rats reveals early vascular abnormalities

Cerebrovascular abnormality is linked to Alzheimer's disease and related dementias (ADRDs). ApoE-Ɛ4 (APOE4) is known to play a critical role in neurovascular dysfunction, however current medical imaging technologies are limited in quantification. This cross-sectional study tested the feasibility of a recently established imaging modality, quantitative ultra-short time-to-echo contrast-enhanced magnetic resonance imaging (QUTE-CE MRI), to identify small vessel abnormality early in development of human APOE4 knock-in female rat (TGRA8960) animal model. At 8 months, 48.3% of the brain volume was found to have significant signal increase (75/173 anatomically segmented regions; q<0.05 for multiple comparisons). Notably, vascular abnormality was detected in the tri-synaptic circuit, cerebellum, and amygdala, all of which are known to functionally decline throughout AD pathology and have implications in learning and memory. The detected abnormality quantified with QUTE-CE MRI is likely a result of hyper-vascularization, but may also be partly, or wholly, due to contributions from blood-brain-barrier leakage. Further exploration with histological validation is warranted to verify the pathological cause. Regardless, these results indicate that QUTE-CE MRI can detect neurovascular dysfunction with high sensitivity with APOE4 and may be helpful to provide new insights into health and disease.

Features of Lipid Metabolism in Humanized ApoE Knockin Rat Models

Apolipoprotein E (ApoE), an essential plasma apolipoprotein, has three isoforms (E2, E3, and E4) in humans. E2 is associated with type III hyperlipoproteinemia. E4 is the major susceptibility gene to Alzheimer’s disease (AD) and coronary heart disease (CHD). We investigated lipid metabolism and atherosclerotic lesions of novel humanized ApoE knockin (hApoE KI) rats in comparison to wide-type (WT) and ApoE knockout (ApoE KO) rats. The hApoE2 rats showed the lowest bodyweight and white fat mass. hApoE2 rats developed higher serum total cholesterol (TC), total triglyceride (TG), and low- and very low density lipoprotein (LDL-C&VLDL-C). ApoE KO rats also exhibited elevated TC and LDL-C&VLDL-C. Only mild atherosclerotic lesions were detected in hApoE2 and ApoE KO aortic roots. Half of the hApoE2 rats developed hepatic nodular cirrhosis. A short period of the Paigen diet (PD) treatment led to the premature death of the hApoE2 and ApoE KO rats. Severe vascular wall thickening of the coronary and pulmonary arteries was observed in 4-month PD-treated hApoE4 rats. In conclusion, hApoE2 rats develop spontaneous hyperlipidemia and might be suitable for studies of lipid metabolism-related diseases. With the PD challenge, hApoE4 KI rats could be a novel model for the analysis of vascular remodeling.

Novel Influences of Sex and APOE Genotype on Spinal Plasticity and Recovery of Function after Spinal Cord Injury

Spinal cord injuries can abolish both motor and sensory function throughout the body. Spontaneous recovery after injury is limited and can vary substantially between individuals. Despite an abundance of therapeutic approaches that have shown promise in preclinical models, there is currently a lack of effective treatment strategies that have been translated to restore function after spinal cord injury (SCI) in the human population. We hypothesized that sex and genetic background of injured individuals could impact how they respond to treatment strategies, presenting a barrier to translating therapies that are not tailored to the individual. One gene of particular interest is APOE, which has been extensively studied in the brain because of its allele-specific influences on synaptic plasticity, metabolism, inflammation, and neurodegeneration. Despite its prominence as a therapeutic target in brain injury and disease, little is known about how it influences neural plasticity and repair processes in the spinal cord. Using humanized mice, we examined how the ε3 and ε4 alleles of APOE influence the efficacy of therapeutic intermittent hypoxia (IH) in inducing spinally-mediated plasticity after cervical SCI (cSCI). IH is sufficient to enhance plasticity and restore motor function after experimental SCI in genetically similar rodent populations, but its effect in human subjects is more variable (Golder and Mitchell, 2005; Hayes et al., 2014). Our results demonstrate that both sex and APOE genotype determine the extent of respiratory motor plasticity that is elicited by IH, highlighting the importance of considering these clinically relevant variables when translating therapeutic approaches for the SCI community.

Differences in Diffusion-Weighted Imaging and Resting-State Functional Connectivity Between Two Culturally Distinct Populations of Prairie Vole

BACKGROUND

We used the highly prosocial prairie vole to test the hypothesis that higher-order brain structure-microarchitecture and functional connectivity (FC)-would differ between males from populations with distinctly different levels of prosocial behavior. Specifically, we studied males from Illinois (IL), which display high levels of prosocial behavior, and first generation males from Kansas dams and IL males (KI), which display the lowest level of prosocial behavior and higher aggression. Behavioral differences between these males are associated with overexpression of estrogen receptor alpha in the medial amygdala and bed nucleus of the stria terminalis and neuropeptide expression in the paraventricular nucleus.

METHODS

We compared apparent diffusion coefficient, fractional anisotropy, and blood oxygen level-dependent resting-state FC between males.

RESULTS

IL males displayed higher apparent diffusion coefficient in regions associated with prosocial behavior, including the bed nucleus of the stria terminalis, paraventricular nucleus, and anterior thalamic nuclei, while KI males showed higher apparent diffusion coefficient in the brainstem. KI males showed significantly higher fractional anisotropy than IL males in 26 brain regions, with the majority being in the brainstem reticular activating system. IL males showed more blood oxygen level-dependent resting-state FC between the bed nucleus of the stria terminalis, paraventricular nucleus, and medial amygdala along with other brain regions, including the hippocampus and areas associated with social and reward networks.

CONCLUSIONS

Our results suggest that gray matter microarchitecture and FC may play a role the expression of prosocial behavior and that differences in other brain regions, especially the brainstem, could be involved. The differences between males suggests that this system represents a potentially valuable model system for studying emotional differences and vulnerability to stress and addiction.