Repeat propofol anesthesia does not exacerbate plaque deposition or synapse loss in APP/PS1 Alzheimer's disease mice.

BACKGROUND: There is increasing interest in whether anesthetic agents affect the risk or progression of Alzheimer's disease (AD). To mitigate many of the methodological issues encountered in human retrospective cohort studies we have used a transgenic model of AD to investigate the effect of propofol on AD pathology. METHODS: Six month-old amyloid precursor protein/presenilin 1 (APP/PS1) transgenic AD mice and control mice were exposed to 3 doses of propofol (200 mg/kg) or vehicle, delivered at monthly intervals. RESULTS: There was no difference in the extent of ß-amyloid (Aß) immunolabeled plaque deposition in APP/PS1 mice in vehicle versus propofol treatment groups. We also detected no difference in plaque-associated synapse loss in APP/PS1 mice following repeat propofol exposure relative to vehicle. Western blotting indicated that there was no difference in post-synaptic density protein 95, synaptophysin or glutamic acid decarboxylase 65/67 expression in control or APP/PS1 mice subjected to repeat propofol treatment relative to vehicle. CONCLUSIONS: These data suggest that repeat propofol anesthesia may not exacerbate plaque deposition or associated synapse loss in AD. Interestingly, this data also provides some of the first evidence suggesting that repeat propofol exposure in adult wild-type mice does not result in robust long-term alterations in the levels of key excitatory and inhibitory synaptic markers.

Wnts are expressed in the spinal cord of adult mice and are differentially induced after injury.

The Wnt family of proteins plays key roles during central nervous system development and has been involved in several neuropathologies during adulthood, including spinal cord injury (SCI). However, Wnts expression knowledge is relatively limited during adult stages. Here, we sought to define the Wnt family expression pattern after SCI in adult mice by using quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Under physiological conditions, the messenger RNAs (mRNAs) of most Wnt ligands, inhibitors, receptors, and coreceptors are constitutively expressed in healthy adult mice. After dorsal hemisection, we found significant time-dependent variations, with a prominent up-regulation of Wnt inhibitory factor 1 (Wif1). IHC against Frizzled (Fz) 1 and Fz4, as representatives of late and acute up-regulated receptors, showed a differential expression in the uninjured spinal cord of Fz1 by neurons and oligodendrocytes and Fz4 by astrocytes. After injury, both receptors were maintained in the same type of cells. Finally, by using BATgal reporter mice, our results revealed active ß-catenin signaling in neurons of the dorsal horn and cells of the central canal of uninjured spinal cords, besides a lack of additional SCI-induced activation. In conclusion, we demonstrate Wnt expression in the adult spinal cord of mice that is modulated by SCI, which differs from that previously described in rats. Further, Fz receptors are differentially expressed by neurons and glial cells, suggestive for cell-specific patterns and thus diverse physiological roles. Further studies will help toward in-depth characterization of the role of all Wnt factors and receptors described and eventually allow for the design of novel therapies.

The Ryk receptor is expressed in glial and fibronectin-expressing cells after spinal cord injury.

Wnt proteins play a critical role in central nervous system development and have been implicated in several neuropathologies, including spinal cord injury (SCI). Ryk, an unconventional Wnt receptor, regulates axonal regeneration after SCI, although its expression pattern in this neuropathology remains unclear. Therefore, we sought to define the spatiotemporal and cellular pattern of Ryk expression after a contusive SCI in adult rats using quantitative reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical analysis. Under physiological conditions, Ryk is expressed in neurons, astrocytes, and blood vessels, but not in oligodendrocytes, microglia, NG2+ glial precursor cells, or axonal projections. Following SCI, we observed an increase in Ryk mRNA expression from 24 h post-injury until 7 days post-injury, whereas its protein levels were significantly augmented at 7 and 14 days post-injury. Moreover, the spatial and cellular Ryk expression pattern was altered in the damaged tissue, where this receptor was observed in reactive astrocytes and microglia/macrophages, NG2+ glial precursors, fibronectin+ cells, oligodendrocytes, and axons. In conclusion, we demonstrate that Ryk is expressed in the unlesioned spinal cord and that, after SCI, its spatiotemporal and cellular expression pattern changed dramatically, being expressed in cells involved in the spinal cord response to damage.

Spatio-temporal expression pattern of frizzled receptors after contusive spinal cord injury in adult rats.

BACKGROUND: Wnt proteins are a large family of molecules that are critically involved in multiple central nervous system (CNS) developmental processes. Experimental evidences suggest a role for this family of proteins in many CNS disorders, including spinal cord injury (SCI), which is a major neuropathology owing to its high prevalence and chronic sensorimotor functional sequelae. Interestingly, most Wnt proteins and their inhibitors are expressed in the uninjured spinal cord, and their temporal expression patterns are dramatically altered after injury. However, little is known regarding the expression of their better-known receptors, the Frizzled family, after SCI. Thus, the aim of the present study was to evaluate the expression of Frizzled receptors in the damaged spinal cord. FINDINGS: Based on the evidence that Wnts are expressed in the spinal cord and are transcriptionally regulated by SCI in adulthood, we analysed the spatio-temporal mRNA and protein expression patterns of Frizzled receptors after contusive SCI using quantitative RT-PCR and single and double immunohistochemistry, respectively. Our results show that almost all of the 10 known Frizzled receptors were expressed in specific spatial patterns in the uninjured spinal cords. Moreover, the Frizzled mRNAs and proteins were expressed after SCI, although their expression patterns were altered during the temporal progression of SCI. Finally, analysis of cellular Frizzled 5 expression pattern by double immunohistochemistry showed that, in the uninjured spinal cord, this receptor was expressed in neurons, oligodendrocytes, astrocytes, microglia and NG2(+) glial precursors. After injury, Frizzled 5 was not only still expressed in oligodendrocytes, astrocytes and NG2(+) glial precursors but also in axons at all evaluated time points. Moreover, Frizzled 5 was expressed in reactive microglia/macrophages from 3 to 14 days post-injury. CONCLUSIONS: Our data suggest the involvement of Frizzled receptors in physiological spinal cord function and in the cellular and molecular events that characterise its neuropathology.

Acute leptin treatment enhances functional recovery after spinal cord injury.

BACKGROUND: Spinal cord injury is a major cause of long-term disability and has no current clinically accepted treatment. Leptin, an adipocyte-derived hormone, is best known as a regulator of food intake and energy expenditure. Interestingly, several studies have demonstrated that leptin has significant effects on proliferation and cell survival in different neuropathologies. Here, we sought to evaluate the role of leptin after spinal cord injury. FINDINGS: Based on its proposed neuroprotective role, we have evaluated the effects of a single, acute intraparenchymal injection of leptin in a clinically relevant animal model of spinal cord injury. As determined by quantitative Real Time-PCR, endogenous leptin and the long isoform of the leptin receptor genes show time-dependent variations in their expression in the healthy and injured adult spinal cord. Immunohistochemical analysis of post-injury tissue showed the long isoform of the leptin receptor expression in oligodendrocytes and, to a lesser extent, in astrocytes, microglia/macrophages and neurons. Moreover, leptin administered after spinal cord injury increased the expression of neuroprotective genes, reduced caspase-3 activity and decreased the expression of pro-inflammatory molecules. In addition, histological analysis performed at the completion of the study showed that leptin treatment reduced microglial reactivity and increased caudal myelin preservation, but it did not modulate astroglial reactivity. Consequently, leptin improved the recovery of sensory and locomotor functioning. CONCLUSIONS: Our data suggest that leptin has a prominent neuroprotective and anti-inflammatory role in spinal cord damage and highlights leptin as a promising therapeutic agent.

Differential expression of Wnts after spinal cord contusion injury in adult rats.

BACKGROUND: Spinal cord injury is a major cause of disability that has no clinically accepted treatment. Functional decline following spinal cord injury is caused by mechanical damage, secondary cell death, reactive gliosis and a poor regenerative capacity of damaged axons. Wnt proteins are a family of secreted glycoproteins that play key roles in different developmental processes although little is known of the expression patterns and functions of Wnts in the adult central nervous system in normal or diseased states. FINDINGS: Using qRT-PCR analysis, we demonstrate that mRNA encoding most Wnt ligands and soluble inhibitors are constitutively expressed in the healthy adult spinal cord. Strikingly, contusion spinal cord injury induced a time-dependent increase in Wnt mRNA expression from 6 hours until 28 days post-injury, and a narrow peak in the expression of soluble Wnt inhibitors between 1 and 3 days post-injury. These results are consistent with the increase in the migration shift, from day 1 to 7, of the intracellular Wnt signalling component, Dishevelled-3. Moreover, after an initial decrease by 1 day, we also found an increase in phosphorylation of the Wnt co-receptor, low-density lipoprotein receptor-related protein 6, and an increase in active ß-catenin protein, both of which suffer a dramatic change, from a homogeneous expression pattern in the grey matter to a disorganized injury-induced pattern. CONCLUSIONS: Our results suggest a role for Wnts in spinal cord homeostasis and injury. We demonstrate that after injury Wnt signalling is activated via the Wnt/ß-catenin and possibly other pathways. These findings provide an important foundation to further address the function of individual Wnt proteins in vivo and the pathophysiology of spinal cord injury.