Biology subjects

Siddle, K.

Publications and source records attributed to Siddle, K..

3 recordsLinked to original sources

bioRxiv2022

The imprinted Mir483 is a growth suppressor and metabolic regulator functioning through IGF1

Mir483 is a conserved and highly expressed microRNA in placental mammals, embedded within the Igf2 gene. Here, we uncover the control mechanisms and physiological functions of Mir483 in vivo, by generating constitutive loss-of-function and over-expressing mice. Mir483 expression is imprinted and dependent on the Igf2 promoters and Igf2/H19 imprinting control region. Over-expression of Mir483 causes severe mid-gestation fetal, but not placental, growth restriction, and late lethality. Fetal death is prevented by restoring Mir483 to endogenous levels using an inducible transgenic system. Continuous postnatal Mir483 over-expression induces growth stunting, elevated hepatic lipid content, increased adiposity, reduced local and systemic IGF1 levels and increased GH. The growth phenotypes are rescued by IGF1 infusion. Our findings provide evidence for a novel functional antagonism between a growth-suppressor microRNA and its growth-promoter host gene, and suggest that Mir483 evolved to limit excessive tissue growth through repression of IGF ligand signalling.

developmental biology↗

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↗

bioRxiv2017

Evaluation of anti insulin receptor antibodies as potential novel therapies for human insulin receptoropathy

Biallelic loss-of-function mutations in the insulin receptor (INSR) commonly cause extreme insulin resistance and early mortality. Therapeutic options are limited, but anti-INSR antibodies have previously been shown to activate two mutant receptors. This study evaluated four murine anti-INSR monoclonal antibodies, each capable of stimulating wildtype INSR signaling, against ten known pathogenic INSR mutants and one novel mutation, F248C. All the mutant INSR bound antibody. Eight mutants showed antibody-induced autophosphorylation while co-treatment with antibody and insulin increased maximal phosphorylation. After simultaneous knockdown of mouse Insr and expression of mutant INSR in 3T3-L1 adipocytes two antibodies activated signaling via AKT preferentially over signaling via ERK1/2 for seven mutants. Two antibodies (83-7 and 83-14) stimulated glucose uptake via P193L, S323L, F382V, and D707A mutant INSR, with antibody response greater than insulin response for D707A. These findings suggest that selected monoclonal anti-INSR antibodies elicit sufficient signaling by some mutated INSR to be clinically significant.\n\nOne sentence summaryAnti-insulin receptor monoclonal antibodies can activate selected naturally occurring mutated human insulin receptors, raising the prospect of novel therapy for lethal recessive insulin resistance.

cell biology↗