Activating Transcription Factor 3 (ATF3) Protects Retinal Ganglion Cells and Promotes Functional Preservation After Optic Nerve Crush.

Purpose: To investigate the possible role of activating transcription factor 3 (ATF3) in retinal ganglion cell (RGC) neuroprotection and optic nerve regeneration after optic nerve crush (ONC). Methods: Overexpression of proteins of interest (ATF3, phosphatase and tensin homolog [PTEN], placental alkaline phosphatase, green fluorescent protein) in the retina was achieved by intravitreal injections of recombinant adenovirus-associated viruses (rAAVs) expressing corresponding proteins. The number of RGCs and αRGCs was evaluated by immunostaining retinal sections and whole-mount retinas with antibodies against RNA binding protein with multiple splicing (RBPMS) and osteopontin, respectively. Axonal regeneration was assessed via fluorophore-coupled cholera toxin subunit B labeling. RGC function was evaluated by recording positive scotopic threshold response. Results: The level of ATF3 is preferentially elevated in osteopontin+/RBPMS+ αRGCs following ONC. Overexpression of ATF3 by intravitreal injection of rAAV 2 weeks before ONC promoted RBPMS+ RGC survival and preserved RGC function as assessed by positive scotopic threshold response recordings 2 weeks after ONC. However, overexpression of ATF3 and simultaneous downregulation of PTEN, a negative regulator of the mTOR pathway, combined with ONC, only moderately promoted short distance RGC axon regeneration (200 µm from the lesion site) but did not provide additional RGC neuroprotection compared with PTEN downregulation alone. Conclusions: These results reveal a neuroprotective effect of ATF3 in the retina following injury and identify ATF3 as a promising agent for potential treatments of optic neuropathies.

Increased expression of ApoA1 after neuronal injury may be beneficial for healing.

ApoA1 is a player in reverse cholesterol transport that initiates multiple cellular pathways on binding to its receptor ABCA1. Its relation to neuronal injury is however unclear. We found ApoA1 to be increasingly abundant at a later time point in the secondary phase of traumatic spinal cord injury. In a cellular injury model of neuroblastoma, ApoA1 showed an initial diminished expression after infliction of injury, which sharply increased thereafter. Subsequently, ApoA1 was shown to alter wound healing dynamics in neuroblastoma injury model. It was observed that an initial lag in scratch wound closure was followed by rapid healing in the ApoA1 treatment group. Activation of ERK pathway and Actin polymerisation by ApoA1 corroborated its role in healing after neuronal injury. We propose that ApoA1 is increasingly expressed and secreted as a delayed response to neuronal injury, and this is a self-protecting mechanism of the injured system.

Clinical proteomics of enervated neurons.

The dynamic field of neurosciences entails ever increasing search for molecular mechanisms of disease states, especially in the domain of neurodegenerative disorders. The previous century heralded the techniques in proteomics when indexing of the human proteomes relating to various disease conditions became important. Early stage research in certain diseases or pathological conditions requires a more holistic approach of first discovering the proteins of interest for the condition. Despite its limitations, proteomics is one of the most powerful techniques available to us today to dissect the molecular scenario in a particular disease situation. In this review we will discuss about the current clinical research in neurodegenerative disorders that employ proteomics techniques. We will specifically focus on our understanding of Alzheimer's disease, traumatic spinal cord injury and neuromyelitis optica. Discussions will include ongoing worldwide research in these areas, research in India and specifically our laboratory in these domains of neurodegenerative conditions.

Possible role of apolipoprotein A1 in healing and cell death after neuronal injury.

Limited axonal regeneration after traumatic injuries to the CNS presents a challenge in neuroscience. Investigation of CSF from subjects with spinal cord injury (SCI) has found that the lipid catabolism pathway is implicated in the post injury scenario. Sequestration of the CNS by the blood brain barrier ensures a mechanism of cholesterol metabolism and recycling distinct from that in the peripheral tissues. Apolipoprotein A1, the protein component of high density lipoprotein (HDL), is an abundant protein in the mammalian cerebrospinal fluid. Interaction of ApoA1 with its cellular receptor, ABCA1, gives rise to several signaling events, such as the activation of Cdc42 protein leading to actin polymerisation. Emerging evidences suggest that ApoA1 mediates anti-inflammatory effects and conversely, is negatively regulated by inflammatory cytokines. Collating these findings, added to the clinical evidences of using HDL as a therapeutic target for cardio vascular diseases, we hypothesize that ApoA1 could be useful in neurite outgrowth after mechanical injury by 1) mediating polymerisation of actin and 2) restricting inflammatory responses after injury which are deleterious to healing.

CSF proteomics of secondary phase spinal cord injury in human subjects: perturbed molecular pathways post injury.

Recovery of sensory and motor functions following traumatic spinal cord injury (SCI) is dependent on injury severity. Here we identified 49 proteins from cerebrospinal fluid (CSF) of SCI patients, eight of which were differentially abundant among two severity groups of SCI. It was observed that the abundance profiles of these proteins change over a time period of days to months post SCI. Statistical analysis revealed that these proteins take part in several molecular pathways including DNA repair, protein phosphorylation, tRNA transcription, iron transport, mRNA metabolism, immune response and lipid and ATP catabolism. These pathways reflect a set of mechanisms that the system may adopt to cope up with the assault depending on the injury severity, thus leading to observed physiological responses. Apart from putting forward a picture of the molecular scenario at the injury site in a human study, this finding further delineates consequent pathways and molecules that may be altered by external intervention to restrict neural degeneration.

Altered levels of amyloid precursor protein intracellular domain-interacting proteins in Alzheimer disease.

BACKGROUND: The amyloid precursor protein intracellular domain (AICD) is an intrinsically unstructured molecule with functional promiscuity that plays an important role in determining the fate of the neurons during its degeneration. Its association with Alzheimer disease (AD) recently played a key role in propelling scientists to choose AICD as a major molecule of interest. Although several studies have been conducted elucidating AICD's participation in inducing neurodegenerative outcomes in AD condition, much remains to be deciphered regarding the linkage of AICD with cellular pathways in the AD scenario. RESULTS: In the present study, we have pulled down interactors of nonphosphorylated AICD from the cerebrospinal fluid of AD subjects, identified them by matrix assisted laser desorption ionization mass spectrometry, and subsequently studied the differential expression of these interactors in AD and control cases by 2-dimensional difference gel electrophoresis. The study has yielded some AICD-interactors that are differentially expressed in the AD cases and are involved in diverse cellular functions. CONCLUSIONS: This proteomic-based approach highlights the first step in finding the possible cellular pathways engaged in AD pathophysiology on the basis of interaction of one or more of their members with AICD.