Biology subjects

Cardozo, C. P.

Publications and source records attributed to Cardozo, C. P..

4 recordsLinked to original sources

bioRxiv2021

RNA-sequencing reveals a gene expression signature in skeletal muscle of a mouse model of age-associated post-operative functional decline

This study aimed to characterize the effects of laparotomy on post-operative physical function and skeletal muscle gene expression in C57BL/6N mice at 3, 20 and 24 months of age to investigate late-life vulnerability and resiliency to acute surgical stress. Pre- and post-operative physical functioning were assessed by forelimb grip strength and motor coordination. Laparotomy induced an age-associated post-operative decline in forelimb grip strength that was greatest in the oldest mice. In contrast, while motor coordination declined with increasing age at baseline, it was unaffected by laparotomy. Moreover, baseline physical function as stratified by motor coordination performance (low vs. high functioning) in 24-month-old mice did not differentially affect post-laparotomy reduction in grip strength. RNA sequencing of soleus muscles showed that laparotomy induced age-associated differential gene expression and canonical pathway activation with the greatest effects in the youngest mice. Examples of such age-associated, metabolically important pathways that were only activated in the youngest mice after laparotomy included oxidative phosphorylation and NRF2-mediated oxidative stress response. Analysis of lipid mediators in serum and gastrocnemius muscle showed alterations in profiles of these mediators during aging and confirmed an association between such changes and functional status in gastrocnemius muscle. These findings demonstrate a mouse model of laparotomy which recapitulated some features of post-operative skeletal muscle decline in older adults following surgery, and identified age-associated, laparotomy-induced molecular signatures in skeletal muscles. Future research can build upon this mouse model to study molecular mechanisms of late-life vulnerability to acute surgical stress and resiliency to counter surgery-induced physical decline.

molecular biology↗

bioRxiv2021

Numb is required for optimal contraction of skeletal muscle

BackgroundThe role of Numb, a protein that is important for cell fate and development was investigated in adult skeletal muscle in mice using a conditional, inducible knockout (cKO) model. MethodsNumb expression was evaluated by Western blot. Numb localization was determined by confocal microscopy. The effects of cKO of Numb and the closely-related gene Numb-like in skeletal muscle fibers was evaluated by in-situ physiology; transmission and focused ion beam scanning electron microscopy; 3-dimensional reconstruction of mitochondrial; lipidomics; and bulk RNA-sequencing. Additional studies using primary mouse myotubes investigated the effects the effects of Numb knockdown on cell fusion, mitochondrial function and calcium transients. ResultsNumb protein expression was reduced by [~]70% (p < 0.01) at 24 as compared to 3 months of age. Numb was localized within muscle fibers as bands traversing fibers at regularly spaced intervals in close proximity to dihydropyridine receptors. The cKO of Numb and Numb-like reduced specific tetanic force by 36%, p < 0.01), altered mitochondrial spatial relationships to sarcomeric structures, increased Z-line spacing by 30% (p < 0.0001), perturbed sarcoplasmic reticulum organization and reduced mitochondrial volume by over 80% (p < 0.01). Only six genes were differentially expressed in cKO mice: Itga4, Sema7a, Irgm2, Vezf1, Mib1 and Tmem132a. Several lipid mediators derived from polyunsaturated fatty acid (PUFAs) through lipoxygenases were upregulated in Numb cKO skeletal muscle; 12-HEPE was increased by [~]250% (p < 0.05) and 17,18-EpETE by [~]240% (p < 0.05). In mouse primary myotubes, Numb knock-down reduced cell fusion ([~]20%, p < 0.01) and mitochondrial function and delayed the caffeine-induced rise in cytosolic calcium concentrations by more than 100% (p < 0.01). ConclusionsThese findings implicate Numb as a critical factor in skeletal muscle structure and function which appear to be critical for calcium release; we therefore speculate Numb plays critical roles in excitation-contraction coupling, one of the putative targets of aged skeletal muscles. These findings provide new insights into the molecular underpinnings of the loss of muscle function observed with sarcopenia.

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↗

bioRxiv2020

The human ApoE4 variant reduces functional recovery and neuronal sprouting after incomplete spinal cord injury in male mice

Spinal cord injury (SCI) is a devastating form of neurotrauma. Patients who carry one or two ApoE4 alleles show worse functional outcomes and longer hospital stays after SCI but the cellular and molecular underpinnings for this genetic link remain poorly understood. Thus, there is a great need to generate animal models to accurately replicate the genetic determinants of outcomes after SCI to spur development of treatments that improve physical function. Here, we examined outcomes after a moderate contusion SCI of transgenic mice expressing human ApoE3 or ApoE4. ApoE4 mice have worse locomotor function and coordination after SCI. Histological examination revealed greater glial staining in ApoE4 mice after SCI associated with reduced levels of neuronal sprouting markers. Bulk RNA sequencing revealed that subcellular processes (SCPs), such as extracellular matrix organization and inflammatory responses, were highly-ranked among upregulated genes at 7 days after SCI in ApoE4 variants. Conversely, SCPs related to neuronal action potential and neuron projection development were increased in ApoE3 mice at 21 days. In summary, our results reveal a clinically relevant SCI mouse model that recapitulates the influence of ApoE genotypes on post-SCI function in individuals who carry these alleles and suggest that the mechanisms underlying worse recovery for ApoE4 animals involve glial activation and loss of sprouting and synaptic activity.

neuroscience↗