The ability to mount a successful stress response in the face of injury is critical to the long-term viability of individual cells and to the organism in general. The stress response, characterized in part by the upregulation of heat shock proteins, is compromised in several neurodegenerative disorders and in some neuronal populations, including motoneurons (MNs). Because astrocytes have a greater capacity than neurons to survive metabolic stress, and because they are intimately associated with the regulation of neuronal function, it is important to understand their stress response, so that we may to better appreciate the impact of stress on neuronal viability during injury or disease. We show that astrocytes subjected to hyperthermia upregulate Hsp/c70 in addition to intracellular signaling components including activated forms of extracellular-signal-regulated kinase (ERK1/2), Akt, and c-jun N-terminal kinase/stress activated protein kinase (JNK/SAPK). Furthermore, astrocytes release increasing amounts of Hsp/c70 into the extracellular environment following stress, an event that is abrogated when signaling through the ERK1/2 and phosphatidylinositol-3 kinase (PI3K) pathways is compromised and enhanced by inhibition of the JNK pathway. Last, we show that the Hsp/c70 is released from astrocytes in exosomes. Together, these data illustrate the diverse regulation of stress-induced Hsp/c70 release in exosomes, and the way in which the balance of activated signal transduction pathways affects this release. These data highlight how stressful insults can alter the microenvironment of an astrocyte, which may ultimately have implications for the survival of neighboring neurons.

Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disorder that results in the progressive loss of motoneurons (MNs) in the CNS. Several survival and death mechanisms of MNs have been characterized and it has been determined that MNs do not appear to mount a complete stress response, as determined by the lack of heat shock protein 70 (Hsp70) upregulation after several stress paradigms. Hsp70 has been shown to confer neuroprotection and the insufficient availability of Hsp70 may contribute to MNs' susceptibility to death in ALS mice. In this study, recombinant human Hsp70 (rhHsp70) was intraperitoneally injected three times weekly, beginning at postnatal day 50 until endstage, to G93A mutant SOD1 (G93A SOD1) mice. The administration of rhHsp70 was effective at increasing lifespan, delaying symptom onset, preserving motor function and prolonging MN survival. Interestingly, injected rhHsp70 localized to skeletal muscle and was not readily detected in the CNS. Treatment with rhHsp70 also resulted in an increased number of innervated neuromuscular junctions compared with control tissue. Together these results suggest rhHsp70 may delay disease progression in the G93A SOD1 mouse via a yet to be identified peripheral mechanism.

The apical ganglion (AG) of larval caenogastropods, such as Ilyanassa obsoleta, houses a sensory organ, contains five serotonergic neurons, innervates the muscular and ciliary components of the velum, and sends neurites into a neuropil that lies atop the cerebral commissure. During metamorphosis, the AG is lost. This loss had been postulated to occur through some form of programmed cell death (PCD), but it is possible for cells within the AG to be respecified or to migrate into adjacent ganglia. Evidence from histological sections is supported by results from a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, which indicate that cells of the AG degenerate by PCD. PCD occurs after metamorphic induction by serotonin or by inhibition of nitric oxide synthase (NOS) activity. Cellular degeneration and nuclear condensation and loss were observed within 12 h of metamorphic induction by NOS inhibition and occur before loss of the velar lobes, the ciliated tissue used for larval swimming and feeding. Velar disintegration happens more rapidly after metamorphic induction by serotonin than by 7-nitroindazole, a NOS inhibitor. Loss of the AG was complete by 72 h after induction. Spontaneous loss of the AG in older competent larvae may arise from a natural decrease in endogenous NOS activity, giving rise to the tendency of aging larvae to display spontaneous metamorphosis in culture.

Abstract:The central nervous system (CNS) of a metamorphically competent larva of the caenogastropod Ilyanassa obsoleta contains a medial, unpaired apical ganglion (AG) of approximately 25 neurons that lies above the commissure connecting the paired cerebral ganglia. The AG, also known as the cephalic or apical sensory organ (ASO), contains numerous sensory neurons and innervates the ciliated velar lobes, the larval swimming and feeding structures. Before metamorphosis, the AG contains 5 serotonergic neurons and exogenous serotonin can induce metamorphosis in competent larvae. The AG appears to be a purely larval structure as it disappears within 3 days of metamorphic induction. In competent larvae, most neurons of the AG display nitric oxide synthase (NOS)-like immunoreactivity and inhibition of NOS activity can induce larval metamorphose. Because nitric oxide (NO) can prevent cells from undergoing apoptosis, a form of programmed cell death (PCD), we hypothesize that inhibition of NOS activity triggers the loss of the AG at the beginning of the metamorphic process. Within 24 hours of metamorphic induction, cellular changes that are typical of the early stages of PCD are visible in histological sections and results of a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay in metamorphosing larvae show AG nuclei containing fragmented DNA, supporting our hypothesis. Keywords: Apoptosis -caenogastropod -mollusc -nitric oxide -serotonin Article: INTRODUCTION Larval Ilyanassa obsoleta, like most marine molluscs, undergo a series of physiological and anatomical transformations at metamorphosis which allow them to begin their juvenile life history phase. The most obvious external change is the loss of the ciliated larval feeding organ or velum [39], which, in the laboratory, occurs with a delay of some 12-36 hours after exposure to an inducing substance. In addition to loss of the velum, within 48 hours of metamorphic induction, internal transformations include rearrangements within the digestive tract and nervous system [13,14,27]. However, until recently, few changes in larval physiology or morphology during the 12-36 hour delay period in I. obsoleta had been described. In this species, by about 83% of larval development [27,42], the CNS contains rudiments of all of the adult ganglia along with a medial, unpaired apical ganglion (AG). Typically, the larval AG innervates the muscular and ciliary components of the velar lobes [20, 29-31, 34, 35]. The AG is an outgrowth of the trochophore apical tuft and has long been postulated to have a sensory function [6,34,35,38]. Recent experiments on a nudibranch provide evidence that the AG can detect a metamorphic cue [17], but a review of literature about molluscan AGs suggests that they are sensorimotor, coordinating the functions of the velar lobes [34,35] and sensing inductive and other stimuli [34]. Currently, the AG appears to be the only part of the larval CNS that is lost at metamorphosis. Some evidence from I. obsoleta and other species suggests t...