Ischemic preconditioning upregulates expression of phospholipase D2 in the rat hippocampus

The Key Role of Initiation Timing on Stroke Rehabilitation by Remote Ischemic Conditioning with Exercise (RICE)

OBJECTIVE

Physical therapy is an integral part of post-stroke rehabilitation. Remote ischemic conditioning (RIC) induces neuroprotection within 24 hours after stroke, during which exercise is unsafe and ineffective. We combined RIC with exercise to establish a novel rehabilitation strategy, RICE (RIC+Exercise). The aim of this study was to optimize the RICE protocol in neurorehabilitation.

METHODS

Thirty-two adult male Sprague-Dawley rats were placed in one of four groups: stroke with no rehabilitation or stroke with various RICE protocols. To further understand the mechanisms underlying neurorehabilitation, sixteen adult male Sprague-Dawley were added, each placed in one of two groups: stroke with exerciseor RIC  . Long-term functional outcomes were determined by beam balance, rota-rod, grid walk, forelimb placing, and Morris water maze tests up to 28 days after stroke (p < 0.05). Changes in neuroplasticity including synaptogenesis (assessed by measuring synaptophysin, post-synaptic density protein-95, and brain-derived neutrophic factor), angiogenesis (via vascular endothelial growth factor, Angiopoietin-1, and Angiopoietin-2), and regulatory molecules (including hypoxia inducible factor-1α, phospholipase D2 and the mechanistic target of rapamycin pathway), were all measured at both mRNA and protein levels (p < 0.05).

RESULTS

All rehabilitation groups showed significant improvement in functional outcomes and levels of synaptogenesis and angiogenesis. 5 day RICE groups, in which RIC was started five days prior to exercise, demonstrated the greatest improvement among these parameters. The results also suggested that the HIF-1α/PLD2/mTOR signaling pathway may be implicated in post-stroke neuroplasticity.

CONCLUSIONS

RICE, particularly RIC initiation at hour 6 post-reperfusion followed by exercise on day 5, enhanced post-stroke rehabilitation in rats.

Chronic isolated lightheadedness is a sign of abnormal plasma levels of phospholipids

OBJECTIVE

To evaluate whether Chronic Isolated Light-headedness (CIL) commonly manifested in elderly patients is related with cerebral oxygen insufficiency.

METHODS

In this case-control study, 462 patients (aged 40-83 years) with CIL and 238 clinical data matched controls were enrolled consecutively from January 2011 to September 2014. The plasma levels of "phospholipids with solubility similar to that of lysophosphatidic acid" (PSS-LPA), a surrogate marker for cerebral oxygen insufficiency, were assayed for all subjects to compare the occurrence and severity of CIL with the values of PSS-LPA.

RESULTS

Patients with CIL had significantly higher plasma levels of PSS-LPA than controls, regardless of having or having not psychogenic abnormalities, χ2 = 448, odds ratio (95% CI) = 140 (72-260), P < 0.001; the mean plasma levels, 0.573 vs. 0.290 mmol/L respectively (P < 0.001). Receiver operator characteristic (ROC) analyses showed plasma PSS-LPA was both sensitive and specific for CIL. The area under ROC curve (AUC) was as high as 0.953 (0.938-0.968). The changes in severity of CIL between two separate assays of one month apart were correlated closely with the changes in plasma levels of PSS-LPA for the same patients, correlation coefficient (Spearman) = 0.90, p < 0.001.

CONCLUSIONS

CIL is a manifestation of abnormal plasma levels of phospholipids which suggests cerebral oxygen insufficiency. This new finding shows that cerebral oxygen insufficiency is not rare especially in elderly persons.

Accumulating insights into the role of phospholipase D2 in human diseases

Phospholipase D2 (PLD2) is a lipid-signaling enzyme that produces the signaling molecule phosphatidic acid (PA) by catalyzing the hydrolysis of phosphatidylcholine (PC). The molecular characteristics of PLD2, the mechanisms of regulation of its activity, its functions in the signaling pathway involving PA and binding partners, and its role in cellular physiology have been extensively studied over the past decades. Although several potential roles of PLD2 have been proposed based on the results of molecular and cell-based studies, the pathophysiological functions of PLD2 in vivo have not yet been fully investigated at the organismal level. Here, we address accumulated evidences that provide insight into the role of PLD2 in human disease. We summarize recent studies using animal models that provide direct evidence of the function of PLD2 in several pathological conditions such as vascular disease, immunological disease, and neurological disease. In light of the use of recently developed PLD2-specific inhibitors showing potential in alleviating pathological conditions, improving our understanding of the role of PLD2 in human disease would be necessary to target the regulation of PLD2 activity as a therapeutic strategy.

PLD$ is involved in phagocytosis of microglia: expression and localization changes of PLD4 are correlated with activation state of microglia

Phospholipase D4 (PLD4) is a recently identified protein that is mainly expressed in the ionized calcium binding adapter molecule 1 (Iba1)-positive microglia in the early postnatal mouse cerebellar white matter. Unlike PLD1 and PLD2, PLD4 exhibits no enzymatic activity for conversion of phosphatidylcholine into choline and phosphatidic acid, and its function is completely unknown. In the present study, we examined the distribution of PLD4 in mouse cerebellar white matter during development and under pathological conditions. Immunohistochemical analysis revealed that PLD4 expression was associated with microglial activation under such two different circumstances. A primary cultured microglia and microglial cell line (MG6) showed that PLD4 was mainly present in the nucleus, except the nucleolus, and expression of PLD4 was upregulated by lipopolysaccharide (LPS) stimulation. In the analysis of phagocytosis of LPS-stimulated microglia, PLD4 was co-localized with phagosomes that contained BioParticles. Inhibition of PLD4 expression using PLD4 specific small interfering RNA (siRNA) in MG6 cells significantly reduced the ratio of phagocytotic cell numbers. These results suggest that the increased PLD4 in the activation process is involved in phagocytosis of activated microglia in the developmental stages and pathological conditions of white matter.

Neuronal plasticity after ischemic preconditioning and TIA-like preconditioning ischemic periods

Transient ischemic attacks (TIAs) have recently become the center of attention since they are thought to share some characteristics with experimental ischemic preconditioning (IPC). This phenomenon describes the situation that a brief, per se harmless, cerebral ischemic period renders the brain resistant to a subsequent severe and normally damaging ischemia. Preconditioning (PC) is not restricted to the brain but also occurs in other organs. Furthermore, apart from a short ischemia, the PC event may comprise nearly any noxious stimulus which, however, must not exceed the threshold to tissue damage. In the last two decades, our knowledge concerning the underlying molecular basis of PC has substantially grown and there is hope to potentially imitate the induction of an endogenous neuroprotective state in patients with a high risk of cerebral ischemia. While, at present, there is virtually no neuropathological data on changes after TIAs or TIA-like PC ischemic periods in human brains, the following review will briefly summarize the current knowledge of plastic neuronal changes after PC in animal models, still awaiting their detection in the human brain.