Yaoxian Liang

Prophylactic angiotensin type 1 receptor antagonism confers neuroprotection in an aged rat model of postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a common geriatric complication, although its exact neuropathogenesis remains elusive. Blockers of the renin-angiotensin system (RAS) ameliorate cognitive deficits in inflammatory brain disorders, with its effects on POCD not yet fully elucidated. The aim of the present study was to investigate regulation of the brain RAS and the effect of angiotensin II receptor type 1 (AT1) inhibition on surgery-induced cognitive impairment in a well-established rat POCD model. We observed upregulation of angiotensin II protein expression and AT1 subtype B transcript levels in the hippocampus after laparotomy, suggesting surgical stress activates the hippocampal RAS in aged rats. Chronic pretreatment with 0.1 mg/kg/day candesartan, an AT1 antagonist, significantly attenuated surgery-induced cognitive deficits in the Morris water maze task without altering blood pressure. Candesartan also decreased hippocampal blood-brain barrier (BBB) permeability. Concomitant with these functional benefits, we observed significant inhibition of hippocampal neuroinflammation, evidenced by decreased glial reactivity and phosphorylation of the NF-κB p65 subunit, as well as marked reductions in interleukin-1β, tumor necrosis factor-α, and cyclooxygenase-2. Our results are the first to show that activation of the brain RAS after surgery contributes to POCD in aged rats. Chronic treatment with low doses of candesartan may elicit blood pressure-independent neuroprotective effects in POCD by improving BBB function and promoting resolution of neuroinflammation.

Surgery-Induced Hippocampal Angiotensin II Elevation Causes Blood-Brain Barrier Disruption via MMP/TIMP in Aged Rats

Reversible blood-brain barrier (BBB) disruption has been uniformly reported in several animal models of postoperative cognitive dysfunction (POCD). Nevertheless, the precise mechanism underlying this occurrence remains unclear. Using an aged rat model of POCD, we investigated the dynamic changes in expression of molecules involved in BBB disintegration, matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9), as well as three of their endogenous tissue inhibitors of MMP (TIMP-1, -2, -3), and tried to establish the correlation between MMP/TIMP balance and surgery-induced hippocampal BBB disruption. We validated the increased hippocampal expression of angiotensin II (Ang II) and Ang II receptor type 1 (AT1) after surgery. We also found MMP/TIMP imbalance as early as 6 h after surgery, together with increased BBB permeability and decreased expression of Occludin and zonula occludens-1 (ZO-1), as well as increased basal lamina protein laminin at 24 h postsurgery. The AT1 antagonist candesartan restored MMP/TIMP equilibrium and modulated expression of Occludin and laminin, but not ZO-1, thereby improving BBB permeability. These events were accompanied by suppression of the surgery-induced canonical nuclear factor-κB (NF-κB) activation cascade. Nevertheless, AT1 antagonism did not affect nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) expression. Collectively, these findings suggest that surgery-induced Ang II release impairs BBB integrity by activating NF-κB signaling and disrupting downstream MMP/TIMP balance via AT1 receptor.

Urinary angiotensin converting enzyme 2 increases in patients with type 2 diabetic mellitus.

Background/Aims: Angiotensin converting enzyme 2 (ACE2) is highly expressed in the kidney and recognized to be renoprotective by degrading Angiotensin II to Angiotensin (1-7) in diabetic nephropathy. However, little is known about the role of urinary ACE2 (UACE2) in diabetes. The present study was performed to evaluate UACE2 levels in type 2 diabetic patients with various degrees of albuminuria and its associations with metabolic parameters. The effect of RAS inhibitors on UACE2 excretion was also assessed. Methods: A total of 132 type 2 diabetic patients with different degrees of albuminuria and 34 healthy volunteers were studied. UACE2 levels and activity were measured. Results: Compared to healthy controls, UACE2 to creatinine (UACE2/Cr) levels were significantly increased in both albuminuric and non-albuminuric diabetic patients. UACE2/Cr levels were much higher in hypertensive diabetic patients compared with their normotensive counterparts and treatment with RAS inhibitors markedly attenuated the augmentation. Furthermore, UACE2/Cr was positively correlated with fasting blood glucose, hemoglobin A1C (HbA1C), triglyceride, and total cholesterol. In multiple regression analysis, UACE2/Cr was independently predicted by HbA1C and RAS inhibitors treatment. Conclusions: UACE2 increased in type 2 diabetic patients with various degrees of albuminuria and RAS inhibitors suppresses UACE2 excretion. UACE2 might potentially function as a marker for monitoring the metabolic status and therapeutic response of RAS inhibitors in diabetes.

Up-Regulation of Intrarenal Renin- Agiotensin System Contributes to Renal Damage in High-Salt Induced Hypertension Rats

Background/Aims: To investigate the change of intrarenal renin-agiotensin system (RAS) and its role in high-salt induced hypertension. Methods: Wistar rats were divided into normal-salt (NS), high-salt diet (HS) and high-salt diet with Losartan group (HS+L), for 6 weeks. Systolic blood pressure (SBP) was monitored. Blood and urine samples were collected every 2 weeks. Angiotensinogen (AGT) was measured by ELISA. AGT mRNA and protein were measured by real-time PCR and immunohistochemistry. Renin activity and angiotensin II (Ang II) were measured by radioimmunoassay. Results: HS versus NS group, SBP increased from 2nd week (P<0.05), urinary protein increased at 6th week (P<0.05). Although plasma renin, AGT and Ang II had no significant changes (P>0.05), renal cortex renin, AGT, and Ang II increased significantly in HS (P<0.05). In HS+L, Losartan failed to reduce SBP (P>0.05) but abolished the increase of proteinuria (P<0.01), renal cortex renin, AGT, Ang II and urinary AGT reduced (P<0.05) while plasma renin, AGT and Ang II enhanced (P<0.05) when compared with HS. Urinary AGT was positively correlated with renal AGT (r=0.592, P <0.01) and Ang II (r=0.726, P <0.01). Conclusion: Inappropriate response of the renal RAS to a high salt diet may contribute to hypertension and renal damage, and urinary AGT could reflect intrarenal RAS activity.

Duration-dependent regulation of autophagy by isoflurane exposure in aged rats

Current evidence suggests a central role for autophagy in many inflammatory brain disorders, including Alzheimer’s disease (AD). Furthermore, it is also well accepted that some i nhalation anesthetics, such as isoflurane, may cause AD-like neuropathogenesis and resultant postoperative cognitive dysfunction, especially in the elderly population. However, the impact of inhalation anesthetics on autophagic components in the brain remains to be documented. Hence, our objective was to investigate the effects of different durations of isoflurane exposure on hippocampus-dependent learning and hippocampal autophagy in aged rats. Aged Sprague-Dawley rats (20 months old) were randomly exposed to 1.5% isoflurane or 100% oxygen for 1 or 4 h. Animals were then trained in the Morris water maze (4 trials/day for 5 consecutive days). Hippocampal phagophore formation markers, beclin 1 and protein microtubule-associated protein 1 light chain-3B (LC3B), as well as p62, an indicator of autophagic fl ux, were quantifi ed by western blotting. There was no significant difference in the escape latencies and time spent in the target quadrant, as well as hippocampal expression of beclin 1, LC3B-II, and p62 at 24 h post-anesthesia between the 1-h isoflurane-exposed rats and their controls (P >0.05). Four-hour exposure to isofl urane resulted in spatial learning and memory deficits, as evidenced by prolonged escape latencies on days 4 and 5 post-anesthesia and less time spent in the target quadrant than sham-exposed animals (P <0.05). These events were accompanied by a decline in hippocampal expression of LC3B-I, LC3B-II, and beclin 1 24 h after isofl urane (P <0.01 and P <0.05). Nevertheless, no significant change in p62 expression was found. Further kinetics study of autophagic changes induced by 4 h of isofl urane showed a transient upregulation of LC3B-I, LC3B-II, and beclin 1 at the end of exposure and a subsequent striking decrease w ithin 12–24 h post-anesthesia (P <0.05). Hippocampal p62 p eaked at 6 h but subsequently resolved. These results from our pilot in vivo study support a duration-dependent relationship between 1.5% isoflurane exposure, and s patial cognitive function as well as hippocampal phagophore formation.

Expression of immunoglobulin A in human mesangial cells and its effects on cell apoptosis and adhesion

IgA nephropathy (IgAN) is characterized by predominant IgA deposition in the glomerular mesangium. It has been considered that the deposited IgA is synthesized by B cells, although recent reports have suggested the implication of other cell types. Therefore, the present study investigated whether glomerular mesangial cells could produce IgA by themselves. Semi-quantitative reverse transcription-polymerase chain reaction, and immunostaining analysis revealed that the IgA protein and gene transcripts were expressed in primary human renal mesangial cells (HRMCs). Furthermore, the IgA heavy chain (α1 and α2) and the light chain (κ and λ) were localized in the cytoplasm or were located on the cell membranes of human mesangial cells (HMCs). Mass spectrometry results indicated that Ig α1 and Ig α2 were secreted in the culture media of HMCs. The transcripts of Ig α, Ig κ and Ig λ constant regions were detected. The predominant rearrangement pattern of the variable region of Ig κ, was Vκ3-20*01/Jκ1*01 in HMCs and Vκ1-12*01/Jκ4*01 in HRMCs. In addition, knockdown of Ig α1 expression by small interfering RNA (siRNA) inhibited cell adhesion and promoted apoptosis. Our findings demonstrate that HMCs can express IgA, and that this expression is associated with cell functions, which may contribute to the deposition of IgA in patients with IgAN.

Expression of immunoglobulin G in human podocytes, and its role in cell viability and adhesion

Podocyte injury occurs during the initiation and development of numerous forms of glomerular disease, and antibodies targeting podocytes have become a biomarker for diagnosis and monitoring treatment response. Accumulating evidence has suggested that immunoglobulin (Ig) is expressed in non-B lineage cells, including epithelial cancer cells, myeloid cells and several types of normal cells. The main aim of the present study was to ascertain the expression of IgG in human podocytes and to determine its potential role in cellular bioactivity. The present study detected positive staining for IgG heavy chain (Igγ) and its subtype γ4, and the light chains κ and λ in the cytoplasm or on the membrane by immunofluorescence. In addition, positive bands were detected for Igγ, γ1, γ3, γ4, κ and λ in the lysates of a podocyte cell line by western blotting. Mass spectrometry confirmed IgG1 as an intact tetramer in the culture supernatant. Constant region transcripts of Igγ, γ1, γ3, γ4, κ and λ were identified by reverse transcription-polymerase chain reaction, and DNA sequencing of these transcripts revealed 96–99% similarity with Ig mRNAs in the National Center for Biotechnology Information database. Compared with the diverse gene rearrangements from B cell-derived Ig, podocyte-derived Ig exhibited conservative V(D)J patterns in the variable regions of Igγ and κ chains. Furthermore, the present study investigated the mechanism underlying IgG production in these cells by examining the expression of recombination activating gene (RAG)1, RAG2 and activation-induced cytidine deaminase. The expression levels of these proteins suggested that podocyte-derived Ig and traditional Ig may be generated in a similar manner. Furthermore, small interfering RNA-mediated downregulation of IgG expression reduced podocyte viability and adhesive capabilities. These findings suggested that IgG is expressed in podocytes and that this expression may be associated with podocyte function. Due to its potential biological and clinical significance, this phenomenon warrants further investigation.