Circumventricular organ-hypothalamic circuit endoplasmic reticulum stress drives hepatic steatosis during obesity.

OBJECTIVE: Nonalcoholic fatty liver disease (NAFLD), characterized by excess liver triglyceride accumulation (hepatic steatosis), leads to an increased risk for cardiometabolic diseases and obesity-related mortality. Emerging evidence points to endoplasmic reticulum (ER) stress in the central nervous system as critical in NAFLD pathogenesis. Here, we tested the contribution of ER stress in a circumventricular organ-hypothalamic circuit in NAFLD development during obesity. METHODS: C57BL/6J male mice were fed a high-fat diet (HFD) or normal chow. A combination of histological, viral tracing, intersectional viral targeting, and in vivo integrative physiological approaches were used to examine the role of ER stress in subfornical organ to hypothalamic paraventricular nucleus projecting neurons (SFO➔PVN) in NAFLD during diet-induced obesity. RESULTS: Immunohistochemical analysis revealed marked unfolded protein response activation in the SFO, particularly in excitatory SFO➔PVN neurons of HFD-fed animals. Moreover, intersectional viral inhibition of ER stress in SFO➔PVN neurons resulted in a reduction in hepatomegaly, hepatic steatosis, and a blunted increase in body weight gain during diet-induced obesity, independent of changes in food intake, substrate partitioning, energy expenditure, and ambulatory activity. CONCLUSIONS: These results indicate that ER stress in an SFO➔PVN neural circuit contributes to hepatic steatosis during obesity.

Salient brain entities labelled in P2rx7-EGFP reporter mouse embryos include the septum, roof plate glial specializations and circumventricular ependymal organs.

The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the ionotropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R is known to regulate crucial aspects of neuronal cell biology, including axonal elongation, path-finding, synapse formation and neuroprotection. Moreover, P2X7R modulates neuroinflammation and is posed as a therapeutic target in inflammatory, oncogenic and degenerative disorders. However, the lack of reliable technical and pharmacological approaches to detect this receptor represents a major hurdle in its study. Here, we took advantage of the P2rx7-EGFP reporter mouse, which expresses enhanced green fluorescence protein (EGFP) immediately downstream of the P2rx7 proximal promoter, to conduct a detailed study of its distribution. We performed a comprehensive analysis of the pattern of P2X7R expression in the brain of E18.5 mouse embryos revealing interesting areas within the CNS. Particularly, strong labelling was found in the septum, as well as along the entire neural roof plate zone of the brain, except chorioidal roof areas, but including specialized circumventricular roof formations, such as the subfornical and subcommissural organs (SFO; SCO). Moreover, our results reveal what seems a novel circumventricular organ, named by us postarcuate organ (PArcO). Furthermore, this study sheds light on the ongoing debate regarding the specific presence of P2X7R in neurons and may be of interest for the elucidation of additional roles of P2X7R in the idiosyncratic histologic development of the CNS and related systemic functions.

Transient increase of microglial C1q expression in the circumventricular organs of adult mouse during LPS-induced inflammation.

The circumventricular organs (CVOs) are the brain regions that lack the blood-brain barrier and allow free entry of blood-derived molecules, offering specialized niche to initiate rapid and early neuroinflammatory responses in the brain. Complement component 1q (C1q) is shown to be the first recognition component of the complement pathway and has a crucial function in the brain under pathological conditions. In the present study, we found that C1q expression in CX3CR1-positive microglia was increased in the CVOs and their neighbouring brain regions of adult mice at 1 day after a single administration of 1 mg/kg lipopolysaccharide (LPS), whereas it returned to control levels at 3 days after LPS stimulation. C1q expression was also seen to localize at synapsin-positive presynaptic axonal terminals in various brain regions. Thus, the present study demonstrates a transient upregulation of microglial C1q expression in the CVOs and their adjacent brain regions, indicating that a transient upregulation of C1q is possibly concerned with physiological responses at early phase of brain inflammation. SIGNIFICANCE OF THE STUDY: The circumventricular organs (CVOs) are specialized brain regions that lack the blood-brain barrier (BBB) and initiate neuroinflammatory responses in the brains. The present study showed that the expression of complement protein C1q was highly increased in microglia of the CVOs and their adjacent brain regions. Moreover, C1q expression was observed to localize specifically at presynaptic axonal terminals in the CVOs and their neighbouring brain regions. Thus, the present study indicates that C1q is possibly correlated with physiological responses at early phase of brain inflammation.

Anatomical, molecular and pathological consideration of the circumventricular organs.

BACKGROUND AND PURPOSE: Circumventricular organs (CVOs) are a diverse group of specialised structures characterized by peculiar vascular and position around the third and fourth ventricles of the brain. In humans, these organs are present during the fetal period and some become vestigial after birth. Some, such as the pineal gland (PG), subcommissural organ (SCO) and organum vasculosum of the lamina terminalis (OVLT), which are located around the third ventricle, might be the site of origin of periventricular tumours. In contrast to humans, CVOs are present in the adult rat and can be dissected by laser capture microdissection (LCM). METHODS: In this study, we used LCM and microarrays to analyse the transcriptomes of three CVOs, the SCO, the subfornical organ (SFO) and the PG and the third ventricle ependyma of the adult rat, in order to better characterise these organs at the molecular level. Furthermore, an immunohistochemical study of Claudin-3 (CLDN3), a membrane protein involved in forming cellular tight junctions, was performed at the level of the SCO. RESULTS: This study highlighted some potentially new or already described specific markers of these structures as Erbb2 and Col11a1 in ependyma, Epcam and CLDN3 in the SCO, Ren1 and Slc22a3 in the SFO and Tph, Anat and Asmt in the PG. Moreover, we found that CLDN3 expression was restricted to the apical pole of ependymocytes in the SCO.

Apoptosis and necrosis in the circumventricular organs after experimental subarachnoid hemorrhage as detected with annexin V and caspase 3 immunostaining.

OBJECTIVES: The circumventricular organs (CVOs) are essential for most autonomic and endocrine functions. Trauma and bleeding can affect their function. The aim of this study was to investigate apoptosis and necrosis in CVOs in the early period after experimental subarachnoid hemorrhage (SAH) in rats, using annexin V affinity and caspase 3 immunostaining. METHODS: Three experimental groups were used: Days 1 and 2 after SAH, and a control group, seven Wistar albino rats each. Subarachnoid hemorrhage was accomplished by transclival basilar artery puncture. Rats were perfused with 0.9% NaCl and 0·1M phosphate buffer pH 7.4 until heart stoppage. Apoptosis and necrosis in CVOs were measured by flow cytometry with annexin V staining, and by caspase 3 immunostaining. RESULTS: Apoptosis in the organum vasculosum lamina terminalis (OVLT), median eminence (ME), and area postrema (AP) was significantly higher in the Day 1 group than in the control group. Apoptosis in the subfornicial organ (SFO), OVLT, ME, and AP was significantly higher in the Day 2 group than in the control group. There were significant differences between the Day 1 and Day 2 groups, except for AP. Necrosis in SFO and OVLT was significantly higher in the Day 2 group than in the Day 1 or control groups, whereas necrosis in the ME and AP did not differ between the three groups. Caspase 3-positive cell density was more intense in the Day 2 group than in the Day 1 and control groups. DISCUSSION: Prevention of apoptosis may potentially improve impaired functions of CVOs after SAH.