Biology subjects

Jonsson, C.

Publications and source records attributed to Jonsson, C..

3 recordsLinked to original sources

bioRxiv2022

Adipocyte-specific ablation of the Ca2+ pump SERCA2 impairs whole-body metabolic function and reveals the diverse metabolic flexibility of white and brown adipose tissue.

ObjectiveSarco/endoplasmic reticulum Ca2+-ATPase (SERCA) transports Ca2+ from the cytosol into the ER and is essential for appropriate regulation of intracellular Ca2+ homeostasis. The objective of this study was to test the hypothesis that SERCA pumps are involved in the regulation of white adipocyte hormone secretion and other aspects of adipose tissue function and that this control is disturbed in obesity-induced type-2 diabetes. MethodsSERCA expression was measured in isolated human and mouse adipocytes as well as in whole mouse adipose tissue by Western blot and RT-qPCR. To test the significance of SERCA2 in adipocyte functionality and whole-body metabolism, we generated adipocyte-specific SERCA2 knockout mice. The mice were metabolically phenotyped by glucose tolerance and tracer studies, histological analyses, measurements of glucose- stimulated insulin release in isolated islets, and gene/protein expression analyses. We also tested the effect of pharmacological SERCA inhibition and genetic SERCA2 ablation in cultured adipocytes. Intracellular and mitochondrial Ca2+ levels were recorded with dual-wavelength ratio imaging and mitochondrial function was assessed by Seahorse technology. ResultsWe demonstrate that SERCA2 is downregulated in white adipocytes from patients with obesity and type-2 diabetes as well as in adipocytes from diet-induced obese mice. SERCA2-ablated adipocytes display disturbed Ca2+ homeostasis associated with upregulated ER stress markers and impaired hormone release. These adipocyte alterations are linked to mild lipodystrophy, reduced adiponectin levels, and impaired glucose tolerance. Interestingly, adipocyte-specific SERCA2 ablation leads to increased glucose uptake in white adipose tissue while glucose uptake is reduced in brown adipose tissue. This dichotomous effect on glucose uptake is due to differently regulated mitochondrial function. In white adipocytes, SERCA2 deficiency triggers an adaptive increase in Fgf21, increased mitochondrial UCP1 levels, and increased oxygen consumption rate (OCR). In contrast, brown SERCA2 null adipocytes display reduced OCR despite increased mitochondrial content and UCP1 levels compared to wild type controls. ConclusionsOur data suggest causal links between reduced white adipocyte SERCA2 levels, deranged adipocyte Ca2+ homeostasis, adipose tissue dysfunction and type-2 diabetes. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=81 SRC="FIGDIR/small/483886v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@ce9737org.highwire.dtl.DTLVardef@129abaeorg.highwire.dtl.DTLVardef@c63342org.highwire.dtl.DTLVardef@4f47fe_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAdipocyte SERCA2 is downregulated in human subjects with type-2 diabetes C_LIO_LILoss of SERCA2 disturbs the intracellular Ca2+ homeostasis in adipocytes C_LIO_LIImpaired metabolism and altered adipokine levels in adipocyte-SERCA2 null mice C_LIO_LILoss of SERCA2 accelerates metabolic processes in white adipocytes C_LIO_LILoss of SERCA2 impairs the mitochondrial function of brown adipocytes C_LI

physiology↗

bioRxiv2022

Time-Dependent Increase in Susceptibility and Severity of Secondary Bacterial Infection during SARS-CoV-2 Infection

Secondary bacterial infections can exacerbate SARS-CoV-2 infection, but their prevalence and impact remain poorly understood. Here, we established that a mild to moderate SARS-CoV-2 infection increased the risk of pneumococcal coinfection in a time-dependent, but sexindependent, manner in the transgenic K18-hACE mouse model of COVID-19. Bacterial coinfection was not established at 3 d post-virus, but increased lethality was observed when the bacteria was initiated at 5 or 7 d post-virus infection (pvi). Bacterial outgrowth was accompanied by neutrophilia in the groups coinfected at 7 d pvi and reductions in B cells, T cells, IL-6, IL-15, IL-18, and LIF were present in groups coinfected at 5 d pvi. However, viral burden, lung pathology, cytokines, chemokines, and immune cell activation were largely unchanged after bacterial coinfection. Examining surviving animals more than a week after infection resolution suggested that immune cell activation remained high and was exacerbated in the lungs of coinfected animals compared with SARS-CoV-2 infection alone. These data suggest that SARS-CoV-2 increases susceptibility and pathogenicity to bacterial coinfection, and further studies are needed to understand and combat disease associated with bacterial pneumonia in COVID-19 patients.

microbiology↗

bioRxiv2018

A Novel Compound, ML336, Inhibits VEEV Replication by Interfering with Viral RNA Synthesis.

Venezuelan equine encephalitis virus (VEEV) is an alphavirus that is endemic to Central and South America. VEEV is known to cause periodic outbreaks of encephalitis in both humans and equids. There are currently no treatments or preventatives for VEEV disease. Our group has previously reported on the development of a novel VEEV inhibitor, ML336, which showed a potent antiviral effect in cell culture models. However, the mechanism of action had yet to be elucidated. Based on the discovery of mutations conferring resistance within nonstructural proteins, we hypothesized that ML336 inhibits viral RNA synthesis. We found that ML336 was able to inhibit VEEV RNA synthesis with an IC50 value of 1.1 nM in a metabolic labelling assay. ML336 marginally affected cellular transcription at levels 20,000-fold above the IC50, and did not show any cytotoxicity up to 50 {micro}M. Using a combination of fluorography, strand-specific qRT-PCR, and a metabolic labelling assay, we found that ML336 inhibits the synthesis of all forms of VEEV RNA. Structural analogues of ML336 showed a correlation between their RNA synthesis inhibitory activity and their antiviral activity in cells, leading us to propose that the primary mechanism of action of this class of compounds is viral RNA synthesis inhibition. The activities of ML336 were highly specific to VEEV, without measurable activity against Chikungunya virus. ML336 was efficacious even in a cell-free viral RNA synthesis assay, suggesting a direct interaction with viral proteins.\n\nImportanceVenezuelan equine encephalitis virus (VEEV) is a pathogenic alphavirus that circulates in the Americas which can cause a lethal encephalitis in humans and equids. There are currently no licensed treatments or vaccines for VEEV. Due to the high potential for aerosol infection and severe outcomes, it is classified as an NIAID Category B agent. To address the unmet need for VEEV antivirals, we continue to advance a novel amidine compound, ML336, through medicinal chemistry and mechanism of action (MOA) studies. Here, we present the molecular MOA by which ML336 inhibits VEEV replication using cellular and biochemical approaches. Our data suggest that ML336 is a direct-acting antiviral that inhibits viral RNA synthesis by interfering with the viral replicase complex. Our studies provide new insights into approaches for the development of novel RNA virus replication inhibitors and the molecular mechanism of alphavirus RNA synthesis.

microbiology↗