Increased aquaporin-1 and Na+ -K+ -2Cl- cotransporter 1 expression in choroid plexus leads to blood-cerebrospinal fluid barrier disruption and necrosis of hippocampal CA1 cells in acute rat models of hyponatremia

Blood-nerve barrier enhances chronic postsurgical pain via the HIF-1α/ aquaporin-1 signaling axis

BACKGROUND

Blood nerve barrier (BNB) participates in the development of neuropathic pain. AQP1 is involved in peripheral pain perception and is negatively correlated with HIF-1α phenotype, which regulates endothelial permeability. However, the role of HIF-1α-AQP1-mediated BNB dysfunction in Chronic Postsurgical Pain (CPSP) has not been reported.

METHODS

Male Sprague-Dawley rats were randomized into 5 groups: (i) Naive group; (ii) Sham group; (iii) SMIR group: skin/muscle incision and retraction for one hour. Behavioral tests were performed for the three groups, BNB vascular permeability and western blotting were conducted to determine HIF-1α and AQP1 protein expression. (iv) The SMIR + HIF-1α inhibitor group; (v) SMIR + DMSO group. Rats in the two groups were administered with HIF-1α inhibitor (2ME2) or DMSO intraperitoneally on the third day post-SMIR surgery followed by performance of behavioral tests, BNB permeability assessment, and determination of HIF-1α, AQP1 and NF200 protein levels.

RESULTS

The permeability of BNB was significantly increased and the expression of AQP1 was downregulated on the 3rd and 7th days post-operation. AQP1 is mainly located in neurons and NF200, CGRP-positive nerve fibers. HIF-1α was highly expressed on the third day post-operation. HIF-1α inhibitor reversed the decrease in AQP1 expression and increase in NF200 expression, barrier permeability and hyperalgesia induced by SMIR on the 3rd day post-surgery.

CONCLUSIONS

Early dysfunction of BNB mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism to promote acute postoperative painful transformation of CPSP. Preadaptive protection of endothelial cells around nerve substructures may be an important countermeasure to inhibit CPSP transformation. Early impairment of BNB function mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism for promoting acute postoperative pain transformation of CPSP.

Progress in Research on TLR4-Mediated Inflammatory Response Mechanisms in Brain Injury after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is one of the common clinical neurological emergencies. Its incidence accounts for about 5-9% of cerebral stroke patients. Even surviving patients often suffer from severe adverse prognoses such as hemiplegia, aphasia, cognitive dysfunction and even death. Inflammatory response plays an important role during early nerve injury in SAH. Toll-like receptors (TLRs), pattern recognition receptors, are important components of the body's innate immune system, and they are usually activated by damage-associated molecular pattern molecules. Studies have shown that with TLR 4 as an essential member of the TLRs family, the inflammatory transduction pathway mediated by it plays a vital role in brain injury after SAH. After SAH occurrence, large amounts of blood enter the subarachnoid space. This can produce massive damage-associated molecular pattern molecules that bind to TLR4, which activates inflammatory response and causes early brain injury, thus resulting in serious adverse prognoses. In this paper, the process in research on TLR4-mediated inflammatory response mechanism in brain injury after SAH was reviewed to provide a new thought for clinical treatment.

AQP4, Astrogenesis, and Hydrocephalus: A New Neurological Perspective

Aquaporin 4 (AQP4) is a cerebral glial marker that labels ependymal cells and astrocytes' endfeet and is the main water channel responsible for the parenchymal fluid balance. However, in brain development, AQP4 is a marker of glial stem cells and plays a crucial role in the pathophysiology of pediatric hydrocephalus. Gliogenesis characterization has been hampered by a lack of biomarkers for precursor and intermediate stages and a deeper understanding of hydrocephalus etiology is needed. This manuscript is a focused review of the current research landscape on AQP4 as a possible biomarker for gliogenesis and its influence in pediatric hydrocephalus, emphasizing reactive astrogliosis. The goal is to understand brain development under hydrocephalic and normal physiologic conditions.

Constitutive activation of canonical Wnt signaling disrupts choroid plexus epithelial fate

The choroid plexus secretes cerebrospinal fluid and is critical for the development and function of the brain. In the telencephalon, the choroid plexus epithelium arises from the Wnt- expressing cortical hem. Canonical Wnt signaling pathway molecules such as nuclear β-CATENIN are expressed in the mouse and human embryonic choroid plexus epithelium indicating that this pathway is active. Point mutations in human β-CATENIN are known to result in the constitutive activation of canonical Wnt signaling. In a mouse model that recapitulates this perturbation, we report a loss of choroid plexus epithelial identity and an apparent transformation of this tissue to a neuronal identity. Aspects of this phenomenon are recapitulated in human embryonic stem cell derived organoids. The choroid plexus is also disrupted when β-Catenin is conditionally inactivated. Together, our results indicate that canonical Wnt signaling is required in a precise and regulated manner for normal choroid plexus development in the mammalian brain.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.

Neonatal Bartter syndrome with cholelithiasis and hydrocephalus: Rare association

Neonatal Bartter syndrome (NBS) is a rare autosomal recessive renal tubular disorder. This disease is characterized by hypokalemia, hypochloremia, and metabolic alkalosis that is often associated with failure to thrive and recurrent episodes of dehydration. The combination of BS and cholelithiasis in an infant is very rare. Herein, we report a premature male infant with NBS who developed cholelithiasis and hydrocephalus on clinical follow up. We recommend that periodic routine hepatobiliary ultrasonograpic screening for cholelithiasis should be performed in patients with NBS.

Overexpression of aquaporin‑1 aggravates hippocampal damage in mouse traumatic brain injury models

'Secondary insult' following primary traumatic brain injury (TBI), including ischemia and edema, may aggravate brain impairments and affect the outcomes. The hippocampus is particularly sensitive to ischemia or edema due to its selective vulnerability, as neural cells of the hippocampus may be more prone to abnormal function or cell death in response to ischemia and edema. Aquaporin‑1 (AQP‑1) was reported to be associated with cerebral edema; however, the expression and role of AQP‑1 in hippocampal edema following TBI have seldom been investigated. In the current study, BALB/c mouse closed craniocerebral injury models were established and the changes of AQP‑1 expression in hippocampi of mouse models following TBI were investigated. Neurological function and edema formation of the models were evaluated and the apoptotic hippocampal cells were then stained in situ and detected, followed by determination of AQP‑1 expression in the hippocampus using immunohistochemistry and western blot analysis. As a result, the majority of mice in the TBI group were severely injured and hippocampal edema was confirmed. The apoptotic cells increased significantly in the hippocampi of mice in the TBI group compared with those in the sham group (P<0.01) and the apoptotic rate increased gradually in a time‑dependent manner. The expression levels of AQP‑1 in the hippocampi of mice were markedly higher in the TBI group than in the sham group (P<0.05) at various time points and AQP‑1 expression levels peaked one day following TBI. These results indicate that upregulation of AQP‑1 may participate in edema formation and delayed cell death of the hippocampus following TBI and may also be a novel therapeutic target to protect the hippocampus from secondary injury following TBI.

Relationship between hyponatremia and hepatic encephalopathy and renal function in patients with decompensated cirrhosis

AIM: To explore the relationship between hyponatremia and hepatic encephalopathy and liver and kidney syndrome in patients with decompensated cirrhosis.

METHODS: One hundred and twenty patients with decompensated cirrhosis treated at our hospital were divided into three groups based on the level of serum sodium: mild, moderate and severe hyponatremia groups. Child-Pugh class and MELD score were calculated in all patients. The association of hyponatremia with hepatorenal syndrome and hepatic encephalopathy was analyzed.

RESULTS: Compared to the mild hyponatremia group, Child-Pugh class and MELD score increased significantly in the moderate and severe groups (U = 4.303, 6.317, both P < 0.05); and the increase was more significant in the severe group (U = 2.816, both P < 0.05). The incidences of hepatic encephalopathy and hepatorenal syndrome were significantly lower in the mild group than in the moderate group and the severe group (χ² = 17.912, 76.305, 6.058, 37.502, all P < 0.05), as well as in the moderate group than in the severe group (χ² = 26.531, 21.694, both P < 0.05).

CONCLUSION: The levels of serum sodium are closely related to the occurrence of hepatic encephalopathy and renal function in patients with decompensated cirrhosis. Blood sodium level can be used as a parameter for evaluation of the patient's condition and complications.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

α3Na+/K+-ATPase deficiency causes brain ventricle dilation and abrupt embryonic motility in zebrafish

Na(+)/K(+)-ATPases are transmembrane ion pumps that maintain ion gradients across the basolateral plasma membrane in all animal cells to facilitate essential biological functions. Mutations in the Na(+)/K(+)-ATPase α3 subunit gene (ATP1A3) cause rapid-onset dystonia-parkinsonism, a rare movement disorder characterized by sudden onset of dystonic spasms and slow movements. In the brain, ATP1A3 is principally expressed in neurons. In zebrafish, the transcripts of the two ATP1A3 orthologs, Atp1a3a and Atp1a3b, show distinct expression in the brain. Surprisingly, targeted knockdown of either Atp1a3a or Atp1a3b leads to brain ventricle dilation, a likely consequence of ion imbalances across the plasma membrane that cause accumulation of cerebrospinal fluid in the ventricle. The brain ventricle dilation is accompanied by a depolarization of spinal Rohon-Beard neurons in Atp1a3a knockdown embryos, suggesting impaired neuronal excitability. This is further supported by Atp1a3a or Atp1a3b knockdown results where altered responses to tactile stimuli as well as abnormal motility were observed. Finally, proteomic analysis identified several protein candidates highlighting proteome changes associated with the knockdown of Atp1a3a or Atp1a3b. Our data thus strongly support the role of α3Na(+)/K(+)-ATPase in zebrafish motility and brain development, associating for the first time the α3Na(+)/K(+)-ATPase deficiency with brain ventricle dilation.