Loss of the Wnt/β-catenin pathway in microglia of the developing brain drives pro-inflammatory activation leading to white matter injury

Microglia-mediated neuroinflammation is key in numerous brain diseases including encephalopathy of the preterm born infant. Microglia of the still-developing brain have unique properties but little is known of how they regulate their inflammatory activation. This is important information as every year 9 million preterm born infants acquire persisting neurological injuries associated with encephalopathy and we lack strategies to prevent and treat these injuries. Our study of activation state regulators in immature brain microglia found a robust down-regulation of Wnt/β-catenin pathway receptors, ligands and intracellular signalling members in pro-inflammatory microglia. We undertook our studies initially in a mouse model of microglia-mediated encephalopathy including the clinical hallmarks of oligodendrocyte injury and hypomyelination. We purified microglia from this model and applied a genome-wide transcriptomics analysis validated with quantitative profiling. We then verified that down-regulation of the Wnt/β-catenin signalling cascade is sufficient and necessary to drive microglia into an oligodendrocyte-damaging phenotype using multiple pharmacological and genetic approaches in vitro and in vivo in mice and in humans and zebrafish. We also demonstrated that genomic variance in the WNT/β-catenin pathway is associated with the anatomical connectivity phenotype of the human preterm born infant. This integrated analysis of genomics and connectivity, as a surrogate for oligodendrocyte function/myelination, is agnostic to cell type. However, this data indicates that the WNT pathway is relevant to human brain injury and specifically that WNT variants may be useful clinically for injury stratification and prognosis. Finally, we performed a translational experiment using a BBB penetrant microglia-specific targeting 3DNA nanocarrier to deliver a Wnt agonist specifically and directly to microglia in vivo. Increasing the activity of the Wnt/β-catenin pathway specifically in microglia in our model of microglia-mediated encephalopathy was able to reduce microglial pro-inflammatory activation, prevent the typical hypomyelination and also prevent the long-term memory deficit associated with this hypomyelination. In summary, the canonical Wnt/β-catenin pathway regulates microglial activation and up-regulation of this pathway could be a viable neurotherapeutic strategy

Vascular control of kidney epithelial transporters.

A major pathway in hypertension pathogenesis involves direct activation of ANG II type 1 (AT(1)) receptors in the kidney, stimulating Na(+) reabsorption. AT(1) receptors in tubular epithelia control expression and stimulation of Na(+) transporters and channels. Recently, we found reduced blood pressure and enhanced natriuresis in mice with cell-specific deletion of AT(1) receptors in smooth muscle (SMKO mice). Although impaired vasoconstriction and preserved renal blood flow might contribute to exaggerated urinary Na(+) excretion in SMKO mice, we considered whether alterations in Na(+) transporter expression might also play a role; therefore, we carried out proteomic analysis of key Na(+) transporters and associated proteins. Here, we show that levels of Na(+)-K(+)-2Cl(-) cotransporter isoform 2 (NKCC2) and Na(+)/H(+) exchanger isoform 3 (NHE3) are reduced at baseline in SMKO mice, accompanied by attenuated natriuretic and diuretic responses to furosemide. During ANG II hypertension, we found widespread remodeling of transporter expression in wild-type mice with significant increases in the levels of total NaCl cotransporter, phosphorylated NaCl cotransporter (Ser(71)), and phosphorylated NKCC2, along with the cleaved, activated forms of the α- and γ-epithelial Na(+) channel. However, the increases in α- and γ-epithelial Na(+) channel with ANG II were substantially attenuated in SMKO mice. This was accompanied by a reduced natriuretic response to amiloride. Thus, enhanced urinary Na(+) excretion observed after cell-specific deletion of AT(1) receptors from smooth muscle cells is associated with altered Na(+) transporter abundance across epithelia in multiple nephron segments. These findings suggest a system of vascular-epithelial in the kidney, modulating the expression of Na(+) transporters and contributing to the regulation of pressure natriuresis.NEW & NOTEWORTHY The use of drugs to block the renin-angiotensin system to reduce blood pressure is common. However, the precise mechanism for how these medications control blood pressure is incompletely understood. Here, we show that mice lacking angiotensin receptors specifically in smooth muscle cells lead to alternation in tubular transporter amount and function. Thus, demonstrating the importance of vascular-tubular cross talk in the control of blood pressure