Biology subjects

Harlow, L.

Publications and source records attributed to Harlow, L..

5 recordsLinked to original sources

bioRxiv2023

Muscle-restricted Nox4 knockout partially corrects muscle contractility following spinal cord injury in mice

Spinal cord injury (SCI) results in severe atrophy of skeletal muscle in paralyzed regions, and a decrease in the force generated by muscle per unit of cross-sectional area. Oxidation of skeletal muscle ryanodine 1 receptors (RyR1) reduces contractile force due to reduced binding of calstabin 1 to RyR1 together with altered gating of RyR1. One cause of RyR1 oxidation is NADPH oxidase 4 (Nox4). We have previously shown that in rats, RyR1 was oxidized and bound less calstabin 1 at 56 days after spinal cord injury (SCI) by transection. Here, we used a conditional knock-out mouse model of Nox4 in muscle to investigate the role of Nox4 in reduced muscle specific force after SCI. Peak twitch force in control mice after SCI was reduced by 42% compared to sham-operated controls but was increased by approximately 43% in SCI Nox4 conditional KO mice compared to SCI controls although it remained less than that for sham-operated controls. Unlike what observed in rats, after SCI the expression of Nox4 was not increased in gastrocnemius muscle and binding of calstabin 1 to RyR1 was not reduced in this muscle. The results suggest a link between Nox4 expression in muscle tissue and reduction in muscle twitch force, however further studies are needed to understand the mechanistic basis for this linkage.

physiology↗

bioRxiv2023

Boldine alters serum lipidomic signatures after acute spinal cord transection in male mice

Traumatic spinal cord injury (SCI) results in wide-ranging cellular and systemic dysfunction in the acute and chronic time frames after the injury. Chronic SCI has well-described secondary medical consequences while acute SCI has unique metabolic challenges as a result of physical trauma, in-patient recovery and other post-operative outcomes. Here, we used high resolution mass spectrometry approaches to describe the circulating lipidomic and metabolomic signatures using blood serum from mice 7 d after a complete SCI. Additionally, we probed whether the aporphine alkaloid, boldine, was able to prevent SCI-induced changes observed using these omics platforms. We found that SCI resulted in large-scale changes to the circulating lipidome but minimal changes in the metabolome, with boldine able to reverse or attenuate SCI-induced changes in the abundance of 50 lipids. Multiomic integration using xMWAS demonstrated unique network structures and community memberships across the groups.

physiology↗

bioRxiv2023

Spinal Cord Injury regulates circular RNA expression in axons

IntroductionNeurons transport mRNA and translational machinery to axons for local translation. After spinal cord injury (SCI), de novo translation is assumed to enable neurorepair. Knowledge of the identity of axonal mRNAs that participate in neurorepair after SCI is limited. We sought to identify and understand how axonal RNAs play a role in axonal regeneration. MethodsWe obtained preparations enriched in axonal mRNAs from control and SCI rats by digesting spinal cord tissue with cold-active protease (CAP). The digested samples were then centrifuged to obtain a supernatant that were then sequenced. We used bioinformatics analyses to identify DEGS and map them to various biological processes. We validated the DEGs by RT-qPCR and RNA-scope. ResultsThe supernatant fraction was highly enriched for axonal mRNA. Using Gene Ontology, the second most significant pathway for all differentially expressed genes (DEGs) was axonogenesis. Among the DEGs was Rims2, which is predominately a circular RNA (circRNA) in the CNS. We show that Rims2 RNA within spinal cord axons is circular. We found an additional 200 putative circRNAs in the axonal-enriched fraction. Knockdown in primary rat cortical neurons of the RNA editing enzyme ADAR1, which inhibits formation of circRNAs, significantly increased axonal outgrowth. Focusing on Rims2 we used Circular RNA Interactome to predict that several of the miRNAs that bind to circRims2 also bind to the 3UTR of GAP-43, PTEN or CREB1, all known regulators of axonal outgrowth. Axonally-translated GAP-43 supports axonal elongation and we detect GAP-43 mRNA in the rat axons by RNAscope. DiscussionBy using our method for enrichment of axonal RNA, we detect SCI induced DEGs, including circRNA such as Rims2. Ablation of ADAR1, the enzyme that regulates circRNA formation, promotes axonal outgrowth of cortical neurons. We developed a pathway model using Circular RNA Interactome that indicates that Rims2 through miRNAs can regulate the axonal translation GAP-43 a known regulator of axonal regeneration indicating that axonal mRNA contribute to regeneration.

neuroscience↗

bioRxiv2022

Assessing the impact of boldine on the gastrocnemius using multiomic profiling at 7 and 28 days post-complete spinal cord injury in young male mice

Spinal cord injury (SCI) results in rapid muscle loss. The mechanisms of muscle atrophy have been well-described but there is limited information specific to SCI. Exogenous molecular interventions to slow muscle atrophy in severe-to-complete SCI have been relatively ineffective and the wide-ranging physiologic response to SCI requires the search for novel therapeutic targets. Connexin hemichannels (CxHC) allow non-selective passage of small molecules into and out of the cell. Boldine, a CxHC-inhibiting aporphine found in the boldo tree (Peumus boldus), has shown promising pre-clinical results in slowing atrophy during sepsis and dysferlinopathy. We administered 50 mg/kg/d of boldine to spinal cord transected mice beginning 3 d post-injury. Tissue was collected 7 and 28 d post-SCI and the gastrocnemius was used for multiomic profiling. Boldine did not prevent body or muscle mass loss but attenuated SCI-induced changes in the abundance of proline, phenylalanine, leucine and isoleucine, as well as glucose, 7 d post-SCI. SCI resulted in the differential expression of ~7,700 and ~2,000 genes at 7 and 28 d, respectively, compared to sham animals, with enrichment for pathways associated with ribosome biogenesis, translation and oxidative phosphorylation. Boldine altered the expression of ~150 genes at 7 d and ~110 genes at 28 d post-SCI. Methylation analyses highlighted distinct patterns at both 7 and 28 d following SCI both with and without boldine. Taken together, boldine is not an efficacious therapy to preserve body and muscle mass after complete SCI, though it preserved or attenuated SCI-induced changes across the metabolome, transcriptome and methylome.

physiology↗

bioRxiv2021

Spinal Cord Injury Reduces Serum Levels of Fibroblast Growth Factor-21 and Impairs its Signaling Pathways in Liver and Adipose Tissue in Mice

Spinal cord injury (SCI) results in dysregulation of carbohydrate and lipid metabolism; the underlying cellular and physiological mechanisms remain unclear. Fibroblast growth factor 21 (FGF21) is a circulating protein primarily secreted by the liver that lowers blood glucose levels, corrects abnormal lipid profiles, and mitigates non-alcoholic fatty liver disease. FGF21 acts via activating FGF receptor 1 and {beta}-klotho in adipose tissue and stimulating release of adiponectin from adipose tissue which in turn signals in the liver and skeletal muscle. We examined FGF21/adiponectin signaling after spinal cord transection in mice fed a high fat diet (HFD) or a standard mouse chow. Tissues were collected at 84 days after spinal cord transection or a sham SCI surgery. SCI reduced serum FGF21 levels and hepatic FGF21 expression, as well as {beta}-klotho and FGF receptor-1 (FGFR1) mRNA expression in adipose tissue. SCI also reduced serum levels and adipose tissue mRNA expression of adiponectin and leptin, two major adipokines. In addition, SCI suppressed hepatic type 2 adiponectin receptor (AdipoR2) mRNA expression and PPAR activation in the liver. Post-SCI mice fed a HFD had further suppression of serum FGF21 levels and hepatic FGF21 expression. Elevated serum free fatty acid (FFA) levels after HFD feeding were observed in post-SCI mice but not in shammice, suggesting defective FFA uptake after SCI. Moreover, after SCI several genes that are implicated in insulins action had reduced expression in tissues of interest. These findings suggest that downregulated FGF21/adiponectin signaling and impaired responsiveness of adipose tissues to FGF21 may, at least in part, contribute to the overall picture of metabolic dysfunction after SCI.

physiology↗