Rasal1 regulates calcium dependent neuronal maturation by modifying microtubule dynamics

BACKGROUND

Rasal1 is a Ras GTPase-activating protein which contains C2 domains necessary for dynamic membrane association following intracellular calcium elevation. Membrane-bound Rasal1 inactivates Ras signaling through its RasGAP activity, and through such mechanisms has been implicated in regulating various cellular functions in the context of tumors. Although highly expressed in the brain, the contribution of Rasal1 to neuronal development and function has yet to be explored.

RESULTS

We examined the contributions of Rasal1 to neuronal development in primary culture of hippocampal neurons through modulation of Rasal1 expression using molecular tools. Fixed and live cell imaging demonstrate diffuse expression of Rasal1 throughout the cell soma, dendrites and axon which localizes to the neuronal plasma membrane in response to intracellular calcium fluctuation. Pull-down and co-immunoprecipitation demonstrate direct interaction of Rasal1 with PKC, tubulin, and CaMKII. Consequently, Rasal1 is found to stabilize microtubules, through post-translational modification of tubulin, and accordingly inhibit dendritic outgrowth and branching. Through imaging, molecular, and electrophysiological techniques Rasal1 is shown to promote NMDA-mediated synaptic activity and CaMKII phosphorylation.

CONCLUSIONS

Rasal1 functions in two separate roles in neuronal development; calcium regulated neurite outgrowth and the promotion of NMDA receptor-mediated postsynaptic events which may be mediated both by interaction with direct binding partners or calcium-dependent regulation of down-stream pathways. Importantly, the outlined molecular mechanisms of Rasal1 may contribute notably to normal neuronal development and synapse formation.

SNAP-25, but not SNAP-23, is essential for photoreceptor development, survival, and function in mice

SNARE-mediated vesicular transport is thought to play roles in photoreceptor glutamate exocytosis and photopigment delivery. However, the functions of Synaptosomal-associated protein (SNAP) isoforms in photoreceptors are unknown. Here, we revisit the expression of SNAP-23 and SNAP-25 and generate photoreceptor-specific knockout mice to investigate their roles. Although we find that SNAP-23 shows weak mRNA expression in photoreceptors, SNAP-23 removal does not affect retinal morphology or vision. SNAP-25 mRNA is developmentally regulated and undergoes mRNA trafficking to photoreceptor inner segments at postnatal day 9 (P9). SNAP-25 knockout photoreceptors develop normally until P9 but degenerate by P14 resulting in severe retinal thinning. Photoreceptor loss in SNAP-25 knockout mice is associated with abolished electroretinograms and vision loss. We find mistrafficked photopigments, enlarged synaptic vesicles, and abnormal synaptic ribbons which potentially underlie photoreceptor degeneration. Our results conclude that SNAP-25, but not SNAP-23, mediates photopigment delivery and synaptic functioning required for photoreceptor development, survival, and function.

Interleukin-6 as a marker of Huntington's disease progression: Systematic review and meta-analysis

Huntington's disease (HD) is a rare, inherited disorder with a broad spectrum of manifestations that vary with disease severity and progression. Although genetic testing can readily confirm the initial diagnosis of HD, markers sensitive to HD progression are needed to aid the development of individual treatment plans. The current analysis aims to identify plasma Interleukin-6 (IL-6) as a marker of disease progression in HD patients. A systematic search of PubMed and Medline from conception through October 2021 was conducted. Studies reporting plasma IL-6 levels of mutation-positive HD patients and healthy controls that met inclusion criteria were selected. The search strategy collected 303 studies, 9 of which met analysis inclusion criteria. From included studies, plasma IL-6 levels of 469 individuals with the HD mutation and 206 healthy controls were collected. Plasma IL-6 levels were meta-analytically compared between healthy controls and individuals with the confirmed HD mutation at all stages of disease and correlated to performance on standardized measures of total cognitive and motor function. Plasma IL-6 was significantly increased in HD groups compared to controls (g = 0.73, 95% CI = 0.31,1.16, P < 0.01) and increased significantly throughout most stages of disease progression, notably between pre-manifest and manifest (g = 0.31, 95% CI = 0.04,0.59, P < 0.05) and early and moderate HD stages (g = 0.52, 95% CI = 0.18,0.86, P < 0.01). Significant correlations between plasma IL-6 levels and HD symptomatic progression were identified, with increased cytokine levels associated with more severe motor impairments (r = 0.179, 95% CI = 0.0479,0.304, P = 0.008) and more extreme disabilities in activities of daily living and/or work tasks (r = -0.229, 95% CI = -0.334, -0.119, P < 0.001). Conclusively, plasma IL-6 levels correlate with disease and motor symptom progression and may act as a viable marker for clinical use. Analysis is limited by small study numbers and highlights the need for future work to identify definitive ranges or rates of change of plasma IL-6 levels that correlate to progressive HD disease states.

Neuronal SNAP-23 is critical for synaptic plasticity and spatial memory independently of NMDA receptor regulation

SNARE-mediated membrane fusion plays a crucial role in presynaptic vesicle exocytosis and also in postsynaptic receptor delivery. The latter is considered particularly important for synaptic plasticity and learning and memory, yet the identity of the key SNARE proteins remains elusive. Here, we investigate the role of neuronal synaptosomal-associated protein-23 (SNAP-23) by analyzing pyramidal-neuron specific SNAP-23 conditional knockout (cKO) mice. Electrophysiological analysis of SNAP-23 deficient neurons using acute hippocampal slices showed normal basal neurotransmission in CA3-CA1 synapses with unchanged AMPA and NMDA currents. Nevertheless, we found theta-burst stimulation-induced long-term potentiation (LTP) was vastly diminished in SNAP-23 cKO slices. Moreover, unlike syntaxin-4 cKO mice where both basal neurotransmission and LTP decrease manifested changes in a broad set of behavioral tasks, deficits of SNAP-23 cKO are more limited to spatial memory. Our data reveal that neuronal SNAP-23 is selectively crucial for synaptic plasticity and spatial memory without affecting basal glutamate receptor function.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Doxorubicin chemotherapy-induced "chemo-brain": Meta-analysis

Doxorubicin is a leading chemotherapeutic halting cellular replication and inducing p53-dependent apoptosis in cancerous tissue. Like many chemotherapies, doxorubicin damages healthy tissue throughout the body through cellular mechanisms independent of its chemotherapeutic action. Although cognitive impairment is commonly recorded in patients after chemotherapy, the occurrence of doxorubicin-induced "chemo-brain" is debated, as doxorubicin cannot cross the blood-brain barrier. However, the potential of indirect doxorubicin neurotoxicity remains, providing a foundation for doxorubicin-mediated chemo-brain. We present the first meta-analysis of defined cognitive performance of doxorubicin-treated patients. A search of PubMed and MedLine collected 494 studies, 14 of which met analysis criteria. Performance of 511 doxorubicin-treated women with breast cancer was compared to that of 306 healthy controls across measures of defined cognitive modalities. Treated patients experience significant impairment in global cognition compared to controls (g₌ -0.41, P < 0.001), with select impairment in executive function (g = -0.25, P < 0.0001), language (g = -0.30, P < 0.0001), memory (g = -0.12, P < 0.01) and processing speed (g = -0.28, P < 0.01). Within memory, short-term verbal memory is most significantly affected (g = -0.21, P < 0.01). Impairment in select cognitive modalities (executive function, language, memory, short-term verbal memory, processing speed) is prevalent in doxorubicin-treated patients, with some cognitive functions remaining intact (attention, motor function, visuospatial abilities). This information can guide the development of future interventions to improve quality-of-life (QOL) and doxorubicin-derived therapies that target cytotoxicity to cancerous tissue, avoiding healthy tissue damage, which is mediated by seemingly independent mechanisms.

Seasonal variation of tyrosinase activity in serum

Serum samples for the analysis of tyrosinase activity were obtained from 10 healthy subjects in autumn, winter and summer. Tyrosinase was purified from 100 microl serum by adsorption to concanavalin A sepharose, the tyrosinase adsorbed to the gel being separated from other components by centrifugation. The gel was suspended in a buffer containing 5-hydroxy-indole-3-acetic acid as an antioxidant and incubated for 2 min with L-cysteine and D-L-dopa at 37 degrees C. The 5-S-L-cysteinyl-L-dopa formed was measured by HPLC and electrochemical detection. Tyrosinase has high stereo-specificity for the L-enantiomer of dopa, and correction for non-specific oxidation was made by simultaneous measurement of 5-S-L-cysteinyl-D-dopa formed from D-dopa. Whereas the oxidation of L-dopa catalysed by tyrosinase ws inhibited by L-tyrosine, the non-specific oxidation of D-dopa was not. Mean serum tyrosinase activity was 0.9 nkatal/l in summer, 0.8 nkatal/l in autumn and 0.4 nkatal/l in winter. The range of tyrosinase activity was much higher in summer and autumn than in winter.

Tyrosinase activity in the serum of patients with malignant melanoma

We have recently described a new method for measurement of tyrosinase activity in small amounts of human serum (100 microliters), where the purification of tyrosinase is obtained by adsorption of the enzyme to concanavalin A sepharose. The method, which measures stereospecific dopa oxidation, was used in the winter of 1992-93 for the measurement of activity in serum obtained from 30 healthy subjects and from 10 patients with melanoma metastases. The serum tyrosinase values in the 30 subjects ranged from 0.1 to 1.0 nkatal/l, and the mean value and standard deviation was 0.4 +/- 0.2 nkatal/l. In the 10 patients with melanoma, the tyrosinase serum values ranged from 1.1 to 10.6 nkal/l, and the mean value was 3.1 nkatal/l.

Utilization of glucose by the implanting mouse blastocyst activated by oestrogen

Blastocysts from mice in an experimental delay of implantation increased their oxidation rate of both glucose and fructose when implantation was initiated by an injection of oestrogen. About 18 h after the injection, the rate of glucose oxidation was significantly higher than that of fructose oxidation. Simultaneously with the increase in the rate of glucose oxidation, glycogen granules appeared in the trophoblast cells. In uterine flushings, the amount of glucose increased already at 6 h. This time corresponds to the period when the blastocyst gets activated for implantation. Determination of glucose utilization by the blastocysts demonstrated that 3 h after the oestrogen injection, the utilization was low but that it was markedly increased at 6 and 18 h. It is concluded that at the initiation of implantation, mouse blastocysts prefer glucose to fructose and that the presence of glucose in the secretion and the increased utilization of glucose by blastocysts at this time suggest that this substrate could be one important nutrient for the blastocyst at early implantation. Glucose, however, cannot be the sole factor critical for the activation of the delayed blastocyst.