Signal transducer and activator of transcription-5 mediates neuronal apoptosis induced by inhibition of Rac GTPase activity.

In several neuronal cell types, the small GTPase Rac is essential for survival. We have shown previously that the Rho family GTPase inhibitor Clostridium difficile toxin B (ToxB) induces apoptosis in primary rat cerebellar granule neurons (CGNs) principally via inhibition of Rac GTPase function. In the present study, incubation with ToxB activated a proapoptotic Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and a pan-JAK inhibitor protected CGNs from Rac inhibition. STAT1 expression was induced by ToxB; however, CGNs from STAT1 knock-out mice succumbed to ToxB-induced apoptosis as readily as wild-type CGNs. STAT3 displayed enhanced tyrosine phosphorylation following treatment with ToxB, and a reputed inhibitor of STAT3, cucurbitacin (JSI-124), reduced CGN apoptosis. Unexpectedly, JSI-124 failed to block STAT3 phosphorylation, and CGNs were not protected from ToxB by other known STAT3 inhibitors. In contrast, STAT5A tyrosine phosphorylation induced by ToxB was suppressed by JSI-124. In addition, roscovitine similarly inhibited STAT5A phosphorylation and protected CGNs from ToxB-induced apoptosis. Consistent with these results, adenoviral infection with a dominant negative STAT5 mutant, but not wild-type STAT5, significantly decreased ToxB-induced apoptosis of CGNs. Finally, chromatin immunoprecipitation with a STAT5 antibody revealed increased STAT5 binding to the promoter region of prosurvival Bcl-xL. STAT5 was recruited to the Bcl-xL promoter region in a ToxB-dependent manner, and this DNA binding preceded Bcl-xL down-regulation, suggesting transcriptional repression. These data indicate that a novel JAK/STAT5 proapoptotic pathway significantly contributes to neuronal apoptosis induced by the inhibition of Rac GTPase

An Anthocyanin-enriched Extract from Strawberries Delays Disease Onset and Extends Survival in the hSOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis

Objective: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease resulting from the death of motor neurons in the brain, brain stem, and spinal cord. Several processes such as oxidative stress, neuroinflammation, and neuronal apoptosis, contribute to disease progression. Anthocyanins are flavonoid compounds derived from fruits and vegetables that possess antioxidant, anti-inflammatory, and anti-apoptotic abilities. Thus, these unique compounds may provide therapeutic benefit for the treatment of ALS. Methods: We used the G93A mutant human SOD1 (hSOD1G93A) mouse model of ALS to assess the effects of an anthocyanin-enriched extract from strawberries (SAE) on disease onset and progression. Mice were administered SAE orally beginning at 60 days of age until end-stage such that mice received 2 mg/kg/day of the extract\u27s primary anthocyanin constituent. Clinical indices of disease were assessed until mice were sacrificed at end-stage. Histopathological indices of disease progression were also evaluated at 105 days of age. Results: hSOD1G93A mice supplemented with SAE experienced a marked (∼17 day) delay in disease onset and a statistically significant (∼11 day) extension in survival in comparison to their untreated mutant counterparts. Additionally, SAE-treated hSOD1G93A mice displayed significantly preserved grip strength throughout disease progression. Histopathological analysis demonstrated that SAE supplementation significantly reduced astrogliosis in spinal cord, and preserved neuromuscular junctions (NMJs) in gastrocnemius muscle. Discussion: These data are the first to demonstrate that anthocyanins have significant potential as therapeutic agents in a preclinical model of ALS due to their ability to reduce astrogliosis in spinal cord and preserve NMJ integrity and muscle function. Therefore, further study of these compounds is warranted in additional preclinical models of ALS and other neurodegenerative diseases