Biology subjects

Strickland, A.

Publications and source records attributed to Strickland, A..

12 recordsLinked to original sources

bioRxiv2026

Mitochondrial NAD+ import gates neuronal resilience to active SARM1

SARM1 is an inducible NADase that executes pathological axon degeneration, but how NAD+ destruction causes neuronal failure remains unclear. Because SARM1 is predicted to act outside the mitochondrial matrix, cytosolic NAD+ loss has been viewed as the critical lethal lesion. We show that SARM1 activation rapidly depletes cytosolic and mitochondrial NAD+ and collapses ATP in both compartments, revealing early, coupled metabolic failure. Enhancing mitochondrial NAD+ import through SLC25A51, the mitochondrial NAD+ transporter, preserves mitochondrial NAD+, maintains mitochondrial function, and delays axon degeneration and neuronal death despite ongoing SARM1 activity. Unexpectedly, SLC25A51 restores cytosolic NAD+-dependent metabolism, reversing a glycolytic block and increasing NAD+ synthesis during stress. Glycolytic inhibition attenuates protection, identifying cytosolic metabolic recovery as an important component of neuronal resilience. AAV-SLC25A51 improves function in a chronic SARM1-dependent neuropathy model. Thus, mitochondrial NAD+ import gates SARM1-driven degeneration by limiting coupled mitochondrial-cytosolic metabolic failure, presenting a downstream intervention point for axon preservation.

neuroscience↗

bioRxiv2025

Dysregulated lactate metabolism synergizes with ALS genetic risk factors to accelerate motor decline

Neurons rely on glial lactate shuttling for metabolic support, which declines with aging and in neurodegenerative disease. Full disruption of lactate shuttling in peripheral nerves causes progressive axon degeneration, but we were interested to understand how partial disruption, a scenario more relevant to aging and disease, contributes to neurodegeneration risk. Pyruvate and lactate are interconverted by lactate dehydrogenases (LDHA and LDHB) in both lactate producing and consuming cells. We therefore began by investigating Ldhb knockout mice (loss of LDHA, the dominant LDH in liver and muscle, caused embryonic lethality), and discovered that they develop progressive neuromuscular junction atrophy and functional decline without axon degeneration. Because even Ldhb+/- heterozygosity significantly affects motor behavior, we also wondered about a potential link to congenital disease and pursued this by identifying rare loss-of-function LDHB variants among ALS patients. Next, to better understand how LDHB loss leads to motor decline, we selectively deleted it in defined cell types. SC-specific deletion caused robust motor defects, whereas motor neuron-specific deletion has little effect. Reasoning that neuronal LDHB deficiency could model age-associated decline in lactate metabolism, we asked whether it would interact with ALS genetic risk. Indeed, motor-neuron LDHB deficiency synergizes with relatively mild ALS risk variants-- TDP43Q331Kand Sod1D83G knock-in alleles--to produce early motor neuropathy, indicating that LDHB loss enhances disease risk. These findings establish lactate metabolism as a modifier of motor system vulnerability and highlight it as a therapeutic target in peripheral as well as central neurodegeneration.

neuroscience↗

bioRxiv2024

Suppressing phagocyte activation by overexpressing the phosphatidylserine lipase ABHD12 preserves sarmopathic nerves

Programmed axon degeneration (AxD) is a key feature of many neurodegenerative diseases. In healthy axons, the axon survival factor NMNAT2 inhibits SARM1, the central executioner of AxD, preventing it from initiating the rapid local NAD+ depletion and metabolic catastrophe that precipitates axon destruction. Because these components of the AxD pathway act within neurons, it was also assumed that the timetable of AxD was set strictly by a cell-intrinsic mechanism independent of neuron-extrinsic processes later activated by axon fragmentation. However, using a rare human disease model of neuropathy caused by hypomorphic NMNAT2 mutations and chronic SARM1 activation (sarmopathy), we demonstrated that neuronal SARM1 can initiate macrophage-mediated axon elimination long before stressed-but-viable axons would otherwise succumb to cell-intrinsic metabolic failure. Investigating potential SARM1-dependent signals that mediate macrophage recognition and/or engulfment of stressed-but-viable axons, we found that chronic SARM1 activation triggers axonal blebbing and dysregulation of phosphatidylserine (PS), a potent phagocyte immunomodulatory molecule. Neuronal expression of the phosphatidylserine lipase ABDH12 suppresses nerve macrophage activation, preserves motor axon integrity, and rescues motor function in this chronic sarmopathy model. We conclude that PS dysregulation is an early SARM1-dependent axonal stress signal, and that blockade of phagocytic recognition and engulfment of stressed-but-viable axons could be an attractive therapeutic target for management of neurological disorders involving SARM1 activation.

neuroscience↗

bioRxiv2024

Reduced STMN2 and pathogenic TDP-43, two hallmarks of ALS, synergize to accelerate motor decline in mice

Pathological TDP-43 loss from the nucleus and cytoplasmic aggregation occurs in almost all cases of ALS and half of frontotemporal dementia patients. Stathmin2 (Stmn2) is a key target of TDP-43 regulation and aberrantly spliced Stmn2 mRNA is found in patients with ALS, frontotemporal dementia, and Alzheimers Disease. STMN2 participates in the axon injury response and its depletion in vivo partially replicates ALS-like symptoms including progressive motor deficits and distal NMJ denervation. The interaction between STMN2 loss and TDP-43 dysfunction has not been studied in mice because TDP-43 regulates human but not murine Stmn2 splicing. Therefore, we generated trans-heterozygous mice that lack one functional copy of Stmn2 and express one mutant TDP-43Q331K knock-in allele to investigate whether reduced STMN2 function exacerbates TDP-43-dependent pathology. Indeed, we observe synergy between these two alleles, resulting in an early onset, progressive motor deficit. Surprisingly, this behavioral defect is not accompanied by detectable neuropathology in the brain, spinal cord, peripheral nerves or at neuromuscular junctions (NMJs). However, the trans-heterozygous mice exhibit abnormal mitochondrial morphology in their distal axons and NMJs. As both STMN2 and TDP-43 affect mitochondrial dynamics, and neuronal mitochondrial dysfunction is a cardinal feature of many neurodegenerative diseases, this abnormality likely contributes to the observed motor deficit. These findings demonstrate that partial loss of STMN2 significantly exacerbates TDP-43-associated phenotypes, suggesting that STMN2 restoration could ameliorate TDP-43 related disease before the onset of degeneration.

neuroscience↗

bioRxiv2022

Disruption of lactate metabolism in the peripheral nervous system leads to motor-selective deficits

Schwann cells (SCs) myelinate and provide trophic support to axons in the peripheral nervous system (PNS) and disruption of SC cellular metabolism leads to demyelination and axon degeneration, both symptoms of peripheral neuropathies. The lactate shuttle hypothesis proposes that glycolytic support cells supply lactate to adjacent axons to sustain their high metabolic demands, a process that requires the interconversion of lactate and pyruvate via lactate dehydrogenase (LDH) in both SCs and neurons. To test this hypothesis in the PNS, we selectively knocked out the genes for both LDH enzymes, LDHA and LDHB, in motor neurons (MNs), sensory neurons (SNs), or SCs. Interestingly, motor axons and their synapses progressively degenerate when LDH is deleted from either MNs or SCs; however, defects in sensory axons or their terminals were not observed when LDH was excised from either SNs or SCs. Deletion of LDH in SCs also leads to a decrease in total ATP levels in peripheral nerves despite a marked accumulation of pyruvate and glycolytic intermediates, consistent with the failure of pyruvate to lactate conversion in SCs leading to energetic deficits in axons. These results support a model in which motor axons are more dependent on SC-derived lactate than are sensory axons, a specific dependency that suggests LDH and lactate shuttling influence the course of motor-dominated neuropathies such as ALS.

neuroscience↗

bioRxiv2022

SARM1 promotes axonal, synaptic, and mitochondrial pathologies in Charcot-Marie-Tooth disease type 2A

Charcot-Marie-Tooth disease (CMT) type 2A is an axonal neuropathy caused by mutations in the mitofusin 2 (MFN2) gene. MFN2 mutations result in profound mitochondrial abnormalities, but the mechanism underlying axonal pathology is unknown. SARM1, the central executioner of axon degeneration, can induce neuropathy and is activated by dysfunctional mitochondria. We tested the role of SARM1 in a rat model carrying a dominant CMT2A mutation (Mfn2H361Y) that exhibits progressive dying-back axonal degeneration, NMJ abnormalities, muscle atrophy, and mitochondrial abnormalities, all hallmarks of the human disease. We generated Sarm1 knockout and Mfn2H361Y, Sarm1 double mutant rats and find that deletion of SARM1 rescues axonal, synaptic, and muscle phenotypes, demonstrating that SARM1 induces much of the neuropathology in this model. Despite the presence of mutant Mfn2 protein in these double mutant rats, loss of SARM1 also dramatically suppressed many mitochondrial defects, including the number, size, and cristae density defects of synaptic mitochondria. This surprising finding indicates that dysfunctional mitochondria activate SARM1, and activated SARM1 feeds back on mitochondria to exacerbate mitochondrial pathology. As such, this work identifies SARM1 inhibition as an exciting therapeutic candidate for the treatment of CMT2A and other neurodegenerative diseases with prominent mitochondrial pathology.

neuroscience↗

bioRxiv2022

Loss of Stathmin-2, a hallmark of TDP-43-associated ALS, causes motor neuropathy

TDP-43 mediates proper Stathmin-2 (STMN2) mRNA splicing, and STMN2 protein is reduced in the spinal cord of most ALS patients. To test the hypothesis that STMN2 loss contributes to ALS pathogenesis, we generated constitutive and conditional STMN2 knockout mice. Constitutive STMN2 loss results in early-onset sensory and motor neuropathy featuring impaired motor behavior and dramatic distal neuromuscular junction (NMJ) denervation of fast-fatigable motor units, which are selectively vulnerable in ALS, without axon or motoneuron degeneration. Selective excision of STMN2 in motoneurons leads to similar NMJ pathology. STMN2 KO heterozygous mice, which better model the partial loss of STMN2 protein found in ALS patients, display a slowly progressive, motor-selective neuropathy with functional deficits and NMJ denervation. Thus, our findings strongly support the hypothesis that STMN2 reduction due to TDP-43 pathology contributes to ALS pathogenesis.

neuroscience↗

bioRxiv2022

Macrophage depletion blocks congenital SARM1-dependent neuropathy

Axon loss contributes to many common neurodegenerative disorders. In healthy axons, the axon survival factor NMNAT2 inhibits SARM1, the central executioner of programmed axon degeneration. We identified two rare NMNAT2 missense variants in two brothers afflicted with a progressive neuropathy syndrome. The polymorphisms result in amino acid substitutions, V98M and R232Q, which reduce NMNAT2 NAD+-synthetase activity. We generated a mouse model of the human syndrome and found that Nmnat2V98M/Nmnat2R232Q compound-heterozygous CRISPR mice survive to adulthood but develop progressive motor dysfunction, peripheral axon loss, and macrophage infiltration. These disease phenotypes are all SARM1-dependent. Remarkably, macrophage depletion therapy blocks and reverses neuropathic phenotypes in Nmnat2V98M/R232Q mice, identifying a SARM1-dependent neuroimmune mechanism as a key driver of disease pathogenesis. These findings demonstrate that SARM1 induces an inflammatory neuropathy and highlight the potential of immune therapy to treat this rare syndrome and other neurodegenerative conditions associated with NMNAT2 loss and SARM1 activation.

neuroscience↗

bioRxiv2021

Localization of infection in neonatal rhesus macaques after oral viral challenge

While vertical transmission of human immunodeficiency virus (HIV) can occur in utero and during delivery and through breastfeeding. We utilized Positron Emission Tomography (PET) imaging coupled with fluorescent microscopy of 64Cu-labeled photoactivatable-GFP-HIV (PA-GFP-BaL) to determine how HIV virions distribute and localize in neonatal rhesus macaques two and four hours after oral viral challenge. Our results show that by four hours after oral viral exposure, HIV virions localize to and penetrate the rectal mucosa. We also used a dual viral challenge with a non-replicative viral vector and a replication competent SHIV-1157ipd3N4 to examine viral transduction and dissemination at 96 hours. Our data show that while SHIV-1157ipd3N4 infection can be found in the oral cavity and upper gastrointestinal (GI) tract, the small and large intestine contained the largest number of infected cells. Moreover, we found that T cells were the biggest population of infected immune cells. Thus, thanks to these novel technologies, we are able to visualize and delineate of viral distribution and infection throughout the entire neonatal GI tract during acute viral infection. Author SummaryApproximately 1.8 million children are currently living with human immunodeficiency virus (HIV). While mother-to-child HIV transmission can occur in utero and during delivery, it most commonly occurs through breastfeeding, creating the need to understand how the virus moves throughout the body and infects the infant once breast milk is consumed. Here, we used multiple imaging techniques and PCR to determine how HIV distributes throughout the gastrointestinal tract after oral viral exposure and in which tissues and cell types become acutely infected. We found that HIV rapidly spreads throughout and penetrates the entire gastrointestinal tract as early as four hours after exposure. We also found that the intestine contained the largest number of infected cells at 96 hours and that most cells infected were T cells. Our study shows that these imaging technologies allow for the examination of viral distribution and infection in a rhesus macaque model.

cell biology↗

bioRxiv2021

Neurotoxins subvert the allosteric activation mechanism of SARM1 to induce neuronal loss

SARM1 is an inducible TIR-domain NAD+ hydrolase that mediates pathological axon degeneration. SARM1 is activated by an increased ratio of NMN to NAD+, which competes for binding to an allosteric activating site. When NMN binds, the TIR domain is released from autoinhibition, activating its NAD+ hydrolase activity. The discovery of this allosteric activating site led us to hypothesize that other NAD+-related metabolites might also activate SARM1. Here we show that the nicotinamide analogue 3-acetylpyridine (3-AP), first identified as a neurotoxin in the 1940s, is converted to 3-APMN which activates SARM1 and induces SARM1-dependent NAD+ depletion, axon degeneration and neuronal death. Systemic treatment with 3-AP causes rapid SARM1-dependent death, while local application to peripheral nerve induces SARM1-dependent axon degeneration. We also identify a related pyridine derivative, 2-aminopyridine, as another SARM1-dependent neurotoxin. These findings identify SARM1 as a candidate mediator of environmental neurotoxicity, and furthermore, suggest that SARM1 agonists could be developed into selective agents for neurolytic therapy.

neuroscience↗

bioRxiv2021

Genetic analysis of praziquantel resistance in schistosome parasites implicates a Transient Receptor Potential channel

Mass treatment with praziquantel (PZQ) monotherapy is the mainstay for schistosomiasis treatment. This drug shows imperfect cure rates in the field and parasites showing reduced PZQ response can be selected in the laboratory, but the extent of resistance in Schistosoma mansoni populations is unknown. We examined the genetic basis of variation in PZQ response in a S. mansoni population (SmLE-PZQ-R) selected with PZQ in the laboratory: 35% of these worms survive high dose (73 {micro}g/mL) PZQ treatment. We used genome wide association to map loci underlying PZQ response. The major chr. 3 peak contains a transient receptor potential (Sm.TRPMPZQ) channel (Smp_246790), activated by nanomolar concentrations of PZQ. PZQ response shows recessive inheritance and marker-assisted selection of parasites at a single Sm.TRPMPZQ SNP enriched populations of PZQ-resistant (PZQ-ER) and sensitive (PZQ-ES) parasites showing >377 fold difference in PZQ response. The PZQ-ER parasites survived treatment in rodents better than PZQ-ES. Resistant parasites show 2.25-fold lower expression of Sm.TRPMPZQ than sensitive parasites. Specific chemical blockers of Sm.TRPMPZQ enhanced PZQ resistance, while Sm.TRPMPZQ activators increased sensitivity. A single SNP in Sm.TRPMPZQ differentiated PZQ-ER and PZQ-ES lines, but mutagenesis showed this was not involved in PZQ-response, suggesting linked regulatory changes. We surveyed Sm.TRPMPZQ sequence variation in 259 parasites from the New and Old World revealing one nonsense mutation that results in a truncated protein with no PZQ-binding site. Our results demonstrate that Sm.TRPMPZQ underlies variation in PZQ response in S. mansoni and provides an approach for monitoring emerging PZQ-resistance alleles in schistosome elimination programs. One Sentence SummaryA transient receptor potential channel determines variation in praziquantel-response in Schistosoma mansoni.

genetics↗

bioRxiv2021

Constitutively active SARM1 variants found in ALS patients induce neuropathy

In response to injury, neurons activate a program of organized axon self-destruction initiated by the NAD+ hydrolase SARM1. In healthy neurons SARM1 is autoinhibited, but single amino acid changes can abolish autoinhibition leading to constitutively-active SARM1 enzymes that promote degeneration when expressed in cultured neurons. To investigate whether naturally-occurring human variants might similarly disrupt SARM1 autoinhibition and potentially contribute to risk for neurodegenerative disease, we assayed the enzymatic activity of 29 rare SARM1 alleles identified among 8,507 amyotrophic lateral sclerosis (ALS) patients. Ten missense variants or small in-frame deletions exhibit constitutive NADase activity, including more than half of those that are unique to the ALS patients or that occur in multiple patients. Expression of these constitutively active ALS-associated SARM1 alleles in cultured dorsal root ganglion (DRG) neurons is pro-degenerative and cytotoxic. Intrathecal injection of an AAV expressing the common SARM1 reference allele is innocuous to mice, but a construct harboring SARM1V184G, the constitutively active variant found most frequently in the ALS patients, causes axon loss, motor dysfunction, and sustained neuroinflammation. These results implicate rare hypermorphic SARM1 alleles as candidate genetic risk factors for ALS and other neurodegenerative conditions.

neuroscience↗