Targeting neurons of rat nucleus tractus solitarii with the gene transfer vector adeno-associated virus type 2 to up-regulate neuronal nitric oxide synthase

Selection of a novel cell-internalizing RNA aptamer specific for CD22 antigen in B cell acute lymphoblastic leukemia

Despite improvements in B cell acute lymphoblastic leukemia (B-ALL) treatment, a significant number of patients experience relapse of the disease, resulting in poor prognosis and high mortality. One of the drawbacks of current B-ALL treatments is the high toxicity associated with the non-specificity of chemotherapeutic drugs. Targeted therapy is an appealing strategy to treat B-ALL to mitigate these toxic off-target effects. One such target is the B cell surface protein CD22. The restricted expression of CD22 on the B-cell lineage and its ligand-induced internalizing properties make it an attractive target in cases of B cell malignancies. To target B-ALL and the CD22 protein, we performed cell internalization SELEX (Systematic Evolution of Ligands by EXponential enrichment) followed by molecular docking to identify internalizing aptamers specific for B-ALL cells that bind the CD22 cell-surface receptor. We identified two RNA aptamers, B-ALL1 and B-ALL2, that target human malignant B cells, with B-ALL1 the first documented RNA aptamer interacting with the CD22 antigen. These B-ALL-specific aptamers represent an important first step toward developing novel targeted therapies for B cell malignancy treatments.

Cellular Localization of Acid-Sensing Ion Channel 1 in Rat Nucleus Tractus Solitarii

By determining its cellular localization in the nucleus tractus solitarii (NTS), we sought anatomical support for a putative physiological role for acid-sensing ion channel Type 1 (ASIC1) in chemosensitivity. Further, we sought to determine the effect of a lesion that produces gliosis in the area. In rats, we studied ASIC1 expression in control tissue with that in tissue with gliosis, which is associated with acidosis, after saporin lesions. We hypothesized that saporin would increase ASIC1 expression in areas of gliosis. Using fluorescent immunohistochemistry and confocal microscopy, we found that cells and processes containing ASIC1-immunoreactivity (IR) were present in the NTS, the dorsal motor nucleus of vagus, and the area postrema. In control tissue, ASIC1-IR predominantly colocalized with IR for the astrocyte marker, glial fibrillary acidic protein (GFAP), or the microglial marker, integrin αM (OX42). The subpostremal NTS was the only NTS region where neurons, identified by protein gene product 9.5 (PGP9.5), contained ASIC1-IR. ASIC1-IR increased significantly (157 ± 8.6% of control, p < 0.001) in the NTS seven days after microinjection of saporin. As we reported previously, GFAP-IR was decreased in the center of the saporin injection site, but GFAP-IR was increased in the surrounding areas where OX42-IR, indicative of activated microglia, was also increased. The over-expressed ASIC1-IR colocalized with GFAP-IR and OX42-IR in those reactive astrocytes and microglia. Our results support the hypothesis that ASIC1 would be increased in activated microglia and in reactive astrocytes after injection of saporin into the NTS.

No evidence of a role for neuronal nitric oxide synthase in the nucleus tractus solitarius in ventilatory responses to acute or chronic hypoxia in awake rats

When exposed to a hypoxic environment, the body's first response is a reflex increase in ventilation, termed the hypoxic ventilatory response (HVR). With chronic sustained hypoxia (CSH), such as during acclimatization to high altitude, an additional time-dependent increase in ventilation occurs, which increases the HVR and is termed ventilatory acclimatization to hypoxia (VAH). This secondary increase persists after exposure to CSH and involves plasticity within the circuits in the central nervous system that control breathing. The mechanisms of HVR plasticity are currently poorly understood. We hypothesized that changes in neuronal nitric oxide synthase (nNOS) activity or expression in the nucleus tractus solitarius contribute to this plasticity and underlie VAH in rats. To test this, we treated rats held in normoxia or 10% O2 (CSH, PIO2 = 70 Torr) for 7-9 days and measured ventilation in conscious, unrestrained animals before and after microinjecting the general NOS antagonist L-NG-Nitroarginine methyl ester into the nucleus tractus solitarius (NTS) or systemically injecting the nNOS-specific antagonist S-methyl-l-thiocitrulline. Localization of injection sites in the NTS was confirmed by histology following the experiment. We found that 1) neither NTS-specific nor systemic nNOS antagonism had any effect on hypoxia-mediated changes in breathing or metabolism (P > 0.05), but 2) nNOS protein expression was increased in the middle and caudal NTS by CSH. A persistent HVR after nNOS blockade in the NTS contrasts with results in awake mice, and our findings do not support the hypotheses that nNOS in the NTS contribute to the HVR or VAH in awake rats.

Acid-sensing ion channel 1 and nitric oxide synthase are in adjacent layers in the wall of rat and human cerebral arteries

Extracellular acidification activates a family of proteins known as acid-sensing ion channels (ASICs). One ASIC subtype, ASIC type 1 (ASIC1), may play an important role in synaptic plasticity, memory, fear conditioning and ischemic brain injury. ASIC1 is found primarily in neurons, but one report showed its expression in isolated mouse cerebrovascular cells. In this study, we sought to determine if ASIC1 is present in intact rat and human major cerebral arteries. A potential physiological significance of such a finding is suggested by studies showing that nitric oxide (NO), which acts as a powerful vasodilator, may modulate proton-gated currents in cultured cells expressing ASIC1s. Because both constitutive NO synthesizing enzymes, neuronal nitric oxide synthase (nNOS) and endothelial NOS (eNOS), are expressed in cerebral arteries we also studied the anatomical relationship between ASIC1 and nNOS or eNOS in both rat and human cerebral arteries. Western blot analysis demonstrated ASIC1 in cerebral arteries from both species. Immunofluorescent histochemistry and confocal microscopy also showed that ASIC1-immunoreactivity (IR), colocalized with the smooth muscle marker alpha-smooth muscle actin (SMA), was present in the anterior cerebral artery (ACA), middle cerebral artery (MCA), posterior cerebral artery (PCA) and basilar artery (BA) of rat and human. Expression of ASIC1 in cerebral arteries is consistent with a role for ASIC1 in modulating cerebrovascular tone both in rat and human. Potential interactions between smooth muscle ASIC1 and nNOS or eNOS were supported by the presence of nNOS-IR in the neighboring adventitial layer and the presence of nNOS-IR and eNOS-IR in the adjacent endothelial layer of the cerebral arteries.

Synergistic effects of BDNF and rehabilitative training on recovery after cervical spinal cord injury

Promoting the rewiring of lesioned motor tracts following a spinal cord injury is a promising strategy to restore motor function. For instance, axonal collaterals may connect to spared, lesion-bridging neurons, thereby establishing a detour for descending signals and thus promoting functional recovery. In our rat model of cervical spinal cord injury, we attempted to promote targeted rewiring of the unilaterally injured corticospinal tract (CST) via the spared reticulospinal tract (RtST). To promote new connections between the two tracts in the brainstem, we administered viral vectors producing two neurotrophins. Brain-derived neurotrophic factor (BDNF), a known promotor of collateral growth, was expressed in the motor cortex, and neurotrophin 3 (NT-3), which has chemoattractive properties, was expressed in the reticular formation. Because rehabilitative training has proven to be beneficial in promoting functionally meaningful plasticity following injury, we added training in a skilled reaching task. Different neurotrophin or control treatments with or without training were evaluated. As hypothesized, improvements of motor performance with the injured forelimb following neurotrophin treatment alone were absent or modest compared to untreated controls. In contrast, we found a significant synergistic effect on performance when BDNF treatment was combined with training. The mechanism of this recovery remains unidentified, as histological analyses of CST and RtST collateral projections did not reveal differences among treatment groups. In conclusion, we demonstrate that following a cervical spinal lesion, rehabilitative training is necessary to translate effects of BDNF into functional recovery by mechanisms which are likely independent of collateral sprouting of the CST or RtST into the gray matter.

Decreased expression of neuronal nitric oxide synthase in the nucleus tractus solitarii inhibits sympathetically mediated baroreflex responses in rat

Despite numerous studies it remains controversial whether nitric oxide (NO·) synthesized by neuronal NOS (nNOS) plays an excitatory or inhibitory role in transmission of baroreflex signals in the nucleus tractus solitarii (NTS). In the current studies we sought to test the hypothesis that nNOS is involved in excitation of baroreflex pathways in NTS while excluding pharmacological interventions in assessing the influence of nNOS. We therefore developed, validated and utilized a short hairpin RNA (shRNA) to reduce expression of nNOS in the NTS of rats whose baroreflex activity was then studied. We demonstrate downregulation of nNOS through transduction with adeno-associated virus type 2 (AAV2) carrying shRNA for nNOS. When injected bilaterally into NTS AAV2nNOSshRNA significantly reduced reflex tachycardic responses to acute hypotension while not affecting reflex bradycardic responses to acute increases of arterial pressure. Control animals treated with intravenous propranolol to block sympathetically mediated chronotropic responses manifested the same baroreflex responses as animals that had been treated with AAV2nNOSshRNA. Neither AAV2 eGFP nor AAV2nNOScDNA affected baroreflex responses. Blocking cardiac vagal influences with atropine similarly reduced baroreflex-mediated bradycardic responses to increases in arterial pressure both in control animals and in those treated with AAV2nNOSshRNA. We conclude that NO· synthesized by nNOS in the NTS is integral to excitation of baroreflex pathways involved in reflex tachycardia, a largely sympathetically mediated response, but not reflex bradycardia, a largely parasympathetically mediated response. We suggest that, at the basal state, nNOS is maximally engaged. Thus, its upregulation does not augment the baroreflex.