Biology subjects

Semple, R.

Publications and source records attributed to Semple, R..

3 recordsLinked to original sources

bioRxiv2024

The metabolically protective energy expenditure increase of Pik3r1-related insulin resistance is not explained by Ucp1-mediated thermogenesis

Human SHORT syndrome is caused by dominant negative human PIK3R1 mutations that impair insulin-stimulated phosphoinositide 3-kinase (PI3K) activity. This produces severe insulin resistance (IR) and often reduced adiposity, commonly described as lipodystrophy. However unlike human primary lipodystrophies, SHORT syndrome does not feature fatty liver or dyslipidaemia. Pik3r1Y657*/WT (Pik3r1Y657*) mice metabolically phenocopy humans, moreover exhibiting increased energy expenditure. We have hypothesised that this increased energy expenditure explains protection from lipotoxicity, and suggested that understanding its mechanism may offer novel approaches to mitigating the metabolic syndrome. We thus set out to determine whether increased Ucp1-dependent thermogenesis explains the increased energy expenditure in Pik3r1-related IR. Male and female Pik3r1Y657* mice challenged with a 45% fat diet for 3 weeks at 21{degrees}C showed reduced metabolic efficiency not explained by changes in food intake or physical activity. No changes were seen in thermoregulation, assessed by thermal imaging and a modified Scholander protocol. Ucp1-dependent thermogenesis, assessed by norepinephrine-induced oxygen consumption, was also unaltered. Housing at 30{degrees}C did not alter the metabolic phenotype of male Pik3r1Y657* mice, but led to lowered physical activity in female Pik3r1Y657* mice compared to controls. Nevertheless these mice still exhibited increased energy expenditure. Ucp1-dependent thermogenic capacity at 30{degrees}C was similar in Pik3r1Y657* and WT mice. We conclude that the likely metabolically protective energy leak in Pik3r1-related IR is not caused by Ucp1-mediated BAT hyperactivation, nor impaired thermal insulation. Further metabolic studies are required to seek alternative explanations such as non Ucp1-mediated futile cycling. New and NoteworthyUnderstanding how Pik3r1Y657* mice and humans are protected from lipotoxicity despite insulin resistance may suggest new ways to mitigate metabolic syndrome. We find reduced metabolic efficiency and increased energy expenditure in Pik3r1Y657* mice but no differences in locomotion, thermoregulation or Ucp1-dependent thermogenesis. Protective energy expenditure in Pik3r1-related insulin resistance has an alternative, likely metabolic, explanation

physiology↗

bioRxiv2020

Anti-Insulin receptor antibodies improve hyperglycaemia in a mouse model of human insulin receptoropathy

Loss-of-function mutations in both alleles of the human insulin receptor gene (INSR) cause extreme insulin resistance (IR) and usually death in childhood, with few therapeutic options. Bivalent anti-receptor antibodies can elicit insulin-like signaling by mutant INSR in cultured cells, but whether this translates into meaningful metabolic benefits in vivo, where dynamics of insulin signaling and receptor recycling are more complex, is unknown. To address this we adopted a strategy to model human insulin receptoropathy in mice, using Cre recombinase delivered by adeno-associated virus to knock out endogenous hepatic Insr acutely in floxed Insr mice (L- IRKO+GFP), before adenovirus-mediated add-back of wild-type (WT) or mutant human INSR. Two murine anti-INSR monoclonal antibodies, previously shown to be surrogate agonists for mutant INSR, were then tested by intraperitoneal injections. As expected, L-IRKO+GFP mice showed glucose intolerance and severe hyperinsulinemia, and this was fully corrected by add-back of WT but neither D734A nor S350L mutant INSR. Antibody injection improved glucose tolerance in D734A INSR-expressing mice and reduced hyperinsulinemia in both S350L and D734A INSR-expressing animals, and did not cause hypoglycemia in WT INSR-expressing mice. Antibody treatment also downregulated both wild-type and mutant INSR protein, attenuating its beneficial metabolic effects. Anti-INSR antibodies thus improve IR in an acute model of insulin receptoropathy, but these findings imply a narrow therapeutic window determined by competing effects of antibodies to stimulate receptors and induce their downregulation. One Sentence SummaryBivalent anti-insulin receptor antibodies improve glycaemic control, but downregulate receptor expression, in a novel mouse model of lethal human insulin receptoropathy.

biochemistry↗

bioRxiv2018

Oncogenic PIK3CA promotes cellular stemness in an allele dose-dependent manner

The PIK3CA gene, which encodes the p110 catalytic subunit of PI3-kinase (PI3K), is mutationally activated in cancer and in overgrowth disorders known as PIK3CA-related overgrowth spectrum (PROS). To determine the consequences of genetic PIK3CA activation in a developmental context of relevance to both PROS and cancer, we engineered isogenic human induced pluripotent stem cells (iPSCs) with heterozygous or homozygous knock-in of PIK3CAH1047R. While heterozygous iPSCs remained largely similar to wild-type cells, homozygosity for PIK3CAH1047R caused widespread, cancer-like transcriptional remodeling, partial loss of epithelial morphology, upregulation of stemness markers and impaired differentiation to all three germ layers in vitro and in vivo. Genetic analysis of PIK3CA-associated cancers revealed that 64 % had multiple oncogenic PIK3CA copies (39 %) or additional PI3K signaling pathway-activating \"hits\" (25 %). This contrasts with the prevailing view that PIK3CA mutations occur heterozygously in cancer. Our findings suggest that a PI3K activity threshold determines pathological consequences of oncogenic PIK3CA activation and provide the first insight into the specific role of this pathway in human pluripotent stem cells.

cancer biology↗