(searched for: doi:10.1126/stke.4172007pe73)
Scientific Reports, Volume 10, pp 1-12; https://doi.org/10.1038/s41598-020-78896-w
Cisplatin is a commonly used chemotherapy agent with significant dose-limiting neurotoxicity resulting in peripheral neuropathy. Although it is postulated that formation of DNA-platinum adducts is responsible for both its cytotoxicity in cancer cells and side effects in neurons, downstream mechanisms that lead to distal axonal degeneration are unknown. Here we show that activation of calpains is required for both neurotoxicity and formation of DNA-platinum adduct formation in neurons but not in cancer cells. Furthermore, we show that neurotoxicity of cisplatin requires activation of Sarm1, a key regulator of Wallerian degeneration, as mice lacking the Sarm1 gene do not develop peripheral neuropathy as evaluated by both behavioral or pathological measures. These findings indicate that Sarm1 and/or specific calpain inhibitors could be developed to prevent cisplatin induced peripheral neuropathy.
Acta Neuropathologica, Volume 131, pp 539-548; https://doi.org/10.1007/s00401-016-1538-0
Accruing evidence suggests that prion-like behavior of fibrillar forms of α-synuclein, β-amyloid peptide and mutant huntingtin are responsible for the spread of the lesions that characterize Parkinson disease, Alzheimer disease and Huntington disease, respectively. It is unknown whether these distinct protein assemblies are transported within and between neurons by similar or distinct mechanisms. It is also unclear if neuronal death or injury is required for neuron-to-neuron transfer. To address these questions, we used mouse primary cortical neurons grown in microfluidic devices to measure the amounts of α-synuclein, Aβ42 and HTTExon1 fibrils transported by axons in both directions (anterograde and retrograde), as well as to examine the mechanism of their release from axons after anterograde transport. We observed that the three fibrils were transported in both anterograde and retrograde directions but with strikingly different efficiencies. The amount of Aβ42 fibrils transported was ten times higher than that of the other two fibrils. HTTExon1 was efficiently transported in the retrograde direction but only marginally in the anterograde direction. Finally, using neurons from two distinct mutant mouse strains whose axons are highly resistant to neurodegeneration (WldS and Sarm1−/−), we found that the three different fibrils were secreted by axons after anterograde transport, in the absence of axonal lysis, indicating that trans-neuronal spread can occur in intact healthy neurons. In summary, fibrils of α-synuclein, Aβ42 and HTTExon1 are all transported in axons but in directions and amounts that are specific of each fibril. After anterograde transport, the three fibrils were secreted in the medium in the absence of axon lysis. Continuous secretion could play an important role in the spread of pathology between neurons but may be amenable to pharmacological intervention.
Published: 1 January 2015
Investigative Opthalmology & Visual Science, Volume 56, pp 505-514; https://doi.org/10.1167/iovs.14-15539
To investigate whether activation of Toll-like receptor 3 (TLR3) promotes the degeneration of retinal ganglion cells (RGCs) by upregulating the protein levels of c-jun N-terminal kinase 3 (JNK3). Toll-like receptor 3-specific activator, Poly(I:C) (polyinosinic-polycytidylic acid), or PBS was injected into the vitreous humor of Thy1-YFP mice. At 24, 48, and 72 hours after treatments, degeneration of RGCs was assessed by using antibodies against brain-specific homeobox/POU domain protein 3a (Brn3a). A TLR3-specific inhibitor was injected into the vitreous humor with or without Poly(I:C). Western blot assays were performed to determine relative levels of TLR3, JNK3, pJNK3, and sterile alpha and HEAT/Armadillo motif-containing 1 (SARM1) proteins in retinal protein extracts, and immunohistochemistry assays were performed to determine their cellular localization in the retina. Mouse eyes were treated with Poly(I:C) or PBS along with MitoTracker Red, and colocalization of MitoTracker Red and JNK3 in the retinas was determined by using antibodies against JNK3. Poly(I:C) activated TLR3 and upregulated its downstream target protein JNK3 but not SARM1 in the retina. Poly(I:C) activated TLR3 and upregulated JNK3 specifically in RGCs and promoted a significant degeneration of RGCs over a 72-hour time period. Toll-like receptor 3 upregulated the levels of JNK3 protein in the cytoplasm of RGCs, but not in the mitochondria. Toll-like receptor 3-specific inhibitor downregulated Poly(I:C)-mediated upregulation of JNK3 protein, and, in turn, significantly attenuated TLR3-induced degeneration of RGCs. Results presented in this study show that the activation of TLR3 alone promotes the degeneration of RGCs by upregulating the protein levels of JNK3.
Journal of Molecular Neuroscience, Volume 55, pp 865-71; https://doi.org/10.1007/s12031-014-0440-2
The axon-protective Wallerian degeneration slow (WLD(S)) protein can ameliorate the decline in axonal ATP levels after neurite transection. Here, we tested the hypothesis that this effect is associated with maintenance of mitochondrial respiration and/or glycolysis. We used isolated neurites of superior cervical ganglion (SCG) cultures in the Seahorse XF-24 Metabolic Flux Analyser to determine mitochondrial respiration and glycolysis under different conditions. We observed that both mitochondrial respiration and glycolysis declined significantly during the latent phase of Wallerian degeneration. WLD(S) partially reduced the decline both in glycolysis and in mitochondrial respiration. In addition, we found that depleting NAD levels in uncut cultures led to changes in mitochondrial respiration and glycolysis similar to those rescued by WLD(S) after cut, suggesting that the maintenance of NAD levels in Wld(S) neurites after axonal injury at least partially underlies the maintenance of ATP levels. However, by using another axon-protective mutation (Sarm1(-/-)), we could demonstrate that rescue of basal ECAR (and hence probably glycolysis) rather than basal OCR (mitochondrial respiration) may be part of the protective phenotype to delay Wallerian degeneration. These findings open new routes to study glycolysis and the connection between NAD and ATP levels in axon degeneration, which may help to eventually develop therapeutic strategies to treat neurodegenerative diseases.
Published: 15 September 2013
Molecular Biology of the Cell, Volume 24, pp 2772-2784; https://doi.org/10.1091/mbc.e13-01-0016
Mutations in PTEN-induced putative kinase 1 (PINK1) or parkin cause autosomal recessive forms of Parkinson's disease. Recent work suggests that loss of mitochondrial membrane potential stabilizes PINK1 and that accumulated PINK1 recruits parkin from the cytoplasm to mitochondria for elimination of depolarized mitochondria, which is known as mitophagy. In this study, we find that PINK1 forms a complex with sterile α and TIR motif containing 1 (SARM1) and tumor necrosis factor receptor–associated factor 6 (TRAF6), which is important for import of PINK1 in the outer membrane and stabilization of PINK1 on depolarized mitochondria. SARM1, which is known to be an adaptor protein for Toll-like receptor, binds to PINK1 and promotes TRAF6-mediated lysine 63 chain ubiquitination of PINK1 at lysine 433. Down-regulation of SARM1 and TRAF6 abrogates accumulation of PINK1, followed by recruitment of parkin to damaged mitochondria. Some pathogenic mutations of PINK1 reduce the complex formation and ubiquitination. These results indicate that association of PINK1 with SARM1 and TRAF6 is an important step for mitophagy.
Cell Death & Differentiation, Volume 20, pp 478-489; https://doi.org/10.1038/cdd.2012.144
Following acute-phase infection, activated T cells are terminated to achieve immune homeostasis, failure of which results in lymphoproliferative and autoimmune diseases. We report that sterile α- and heat armadillo-motif-containing protein (SARM), the most conserved Toll-like receptors adaptor, is proapoptotic during T-cell immune response. SARM expression is significantly reduced in natural killer (NK)/T lymphoma patients compared with healthy individuals, suggesting that decreased SARM supports NK/T-cell proliferation. T cells knocked down of SARM survived and proliferated more significantly compared with wild-type T cells following influenza infection in vivo. During activation of cytotoxic T cells, the SARM level fell before rising, correlating inversely with cell proliferation and subsequent T-cell clearance. SARM knockdown rescued T cells from both activation- and neglect-induced cell deaths. The mitochondria-localized SARM triggers intrinsic apoptosis by generating reactive oxygen species and depolarizing the mitochondrial potential. The proapoptotic function is attributable to the C-terminal sterile alpha motif and Toll/interleukin-1 receptor domains. Mechanistically, SARM mediates intrinsic apoptosis via B cell lymphoma-2 (Bcl-2) family members. SARM suppresses B cell lymphoma-extra large (Bcl-xL) and downregulates extracellular signal-regulated kinase phosphorylation, which are cell survival effectors. Overexpression of Bcl-xL and double knockout of Bcl-2 associated X protein and Bcl-2 homologous antagonist killer substantially reduced SARM-induced apoptosis. Collectively, we have shown how T-cell death following infection is mediated by SARM-induced intrinsic apoptosis, which is crucial for T-cell homeostasis.
The Journal of Immunology, Volume 184, pp 6874-6881; https://doi.org/10.4049/jimmunol.0903675
Among five Toll/IL-1R resistance adaptors, sterile α and Toll/IL-1R resistance motif containing protein (SARM) is the only one conserved from Caenorhabditis elegans to human. However, its physiologic roles are hardly understood, and its involvement in TLR signaling remains debatable. In this study, we first demonstrated a predominant expression of amphioxus SARM (Branchiostoma belcheri tsingtauense SARM) in neural cells during embryogenesis and its predominant expression in the digestive system from larva to adult, suggesting its primitive role in neural development and a potential physiologic role in immunity. We further found that B. belcheri tsingtauense SARM was localized in mitochondria and could attenuate the TLR signaling via interacting with amphioxus MyD88 and tumor necrosis receptor associated factor 6. Thus, amphioxus SARM appears unique in that it may play dual functions in neural development and innate immunity by targeting amphioxus TLR signaling.