Deficiency of MicroRNA-181a Results in Transcriptome-Wide Cell-Specific Changes in the Kidney and Increases Blood Pressure

MicroRNA miR-181a is downregulated in the kidneys of hypertensive patients and hypertensive mice. In vitro, miR-181a is a posttranslational inhibitor of renin expression, but pleiotropic mechanisms by which miR-181a may influence blood pressure (BP) are unknown. Here, we determined whether deletion of miR-181a/b-1 in vivo changes BP and the molecular mechanisms involved at the single-cell level. We developed a KO (knockout) mouse model lacking miR-181a/b-1 genes using CRISPR/Cas9 technology. Radiotelemetry probes were implanted in 12-week-old C57BL/6J WT (wild type) and miR-181a/b-1 KO mice. Systolic and diastolic BP were 4- to 5-mm Hg higher in KO compared with WT mice over 24 hours ( P <0.01). Compared with WT mice, renal renin was higher in the juxtaglomerular cells of KO mice. BP was similar in WT mice on a high- (3.1%) versus low- (0.3%) sodium diet (+0.4±0.8 mm Hg), but KO mice showed salt sensitivity (+3.3±0.8 mm Hg; P <0.001). Since microRNAs can target several mRNAs simultaneously, we performed single-nuclei RNA sequencing in 6699 renal cells. We identified 12 distinct types of renal cells, all of which had genes that were dysregulated. This included genes involved in renal fibrosis and inflammation such as Stat4 , Col4a1 , Cd81 , Flt3l , Cxcl16 , and Smad4 . We observed upregulation of pathways related to the immune system, inflammatory response, reactive oxygen species, and nerve development, consistent with higher tyrosine hydroxylase in the kidney. In conclusion, downregulation of the miR-181a gene led to increased BP and salt sensitivity in mice. This is likely due to an increase in renin expression in juxtaglomerular cells, as well as microRNA-driven pleiotropic effects impacting renal pathways associated with hypertension.

Fibroblast-derived HGF integrates muscle and nerve development during morphogenesis of the mammalian diaphragm

The diaphragm is a domed muscle between the thorax and abdomen essential for breathing in mammals. Diaphragm development requires the coordinated development of muscle, connective tissue, and nerve, which are derived from different embryonic sources. Defects in diaphragm development cause the common and often lethal birth defect, Congenital Diaphragmatic Hernias (CDH). HGF/MET signaling is required for diaphragm muscularization, but the source of HGF and the specific functions of this pathway in muscle progenitors or potentially the phrenic nerve have not been explicitly tested. Using conditional mutagenesis and pharmacological inhibition of MET, we demonstrate that the pleuroperitoneal folds (PPFs), transient embryonic structures that give rise to the connective tissue, are the source of HGF critical for diaphragm muscularization and phrenic nerve primary branching. HGF not only is required for recruitment of muscle progenitors to the diaphragm, but is continuously required for maintenance and motility of the pool of progenitors to enable full muscularization. Thus, the connective tissue fibroblasts and HGF coordinately regulate diaphragm muscularization and innervation. Defects in PPF-derived HGF result in muscleless regions that are susceptible to CDH.Summary StatementFibroblast-derived HGF signals to Met+ muscle progenitors and nerve to control the expansion of diaphragm muscle and primary branching of phrenic nerve axons - structures critical for breathing in mammals.

Animal Models as a Tool to Design Therapeutical Strategies for CMT-like Hereditary Neuropathies

Since ancient times, animal models have provided fundamental information in medical knowledge. This also applies for discoveries in the field of inherited peripheral neuropathies (IPNs), where they have been instrumental for our understanding of nerve development, pathogenesis of neuropathy, molecules and pathways involved and to design potential therapies. In this review, we briefly describe how animal models have been used in ancient medicine until the use of rodents as the prevalent model in present times. We then travel along different examples of how rodents have been used to improve our understanding of IPNs. We do not intend to describe all discoveries and animal models developed for IPNs, but just to touch on a few arbitrary and paradigmatic examples, taken from our direct experience or from literature. The idea is to show how strategies have been developed to finally arrive to possible treatments for IPNs.