(Pro)renin Receptor Knockdown in Tyrosine Hydroxylase neurons in the PVN Protects Against the Development of HFD‐Induced Hyperglycemia and Increases Energy Expenditure in Mice
Authors: Worker Caleb , Feng‐Earley Yumei 
Published: May 2022

Type 2 diabetes mellitus (T2D) is the major form of human diabetes, accounting for approximately 90–95% of diagnosed diabetes cases in the United States. The brain renin‐angiotensin system (RAS), traditionally viewed as a cardiovascular regulatory system, has recently emerged as a critical part of metabolic and energy‐expenditure signaling systems in the central nervous system (CNS). The (pro)renin receptor (PRR) is a key component of the brain RAS and plays a pivotal role in the development of hypertension. However, its importance in high fat diet (HFD)‐induced metabolic physiology is not well understood. We recently showed that neuron‐specific PRR deletion (PRRKO) improves fasting blood glucose and glucose tolerance in mice under 16 weeks of HFD. However, the specific neuronal cell types and synaptic mechanisms by which PRR acts is largely unknown. Tyrosine Hydroxylase (TH)‐containing neurons are catecholaminergic neurons found in multiple regulatory nuclei throughout the brain. The TH neurons in the paraventricular nucleus (PVN, THPVN) have been previously implicated in metabolic and cardiovascular control via inhibition of brainstem regulatory nuclei. Accordingly, we hypothesize that PRR in THPVN neurons plays a critical role in the regulation of HFD‐induced hyperglycemia. To test this hypothesis, we injected both male and female TdTomato‐PRR‐LoxP mice with adeno‐associated virus serotype 2 (AAV2)‐mediated Cre‐recombinase driven by a rat TH promoter (AAV2‐TH‐Cre) to ablate PRR in the THPVN neurons (THPVNPRRKO). The Tdtomato‐LoxP mice received the same virus were used as control. Fasting blood glucose (FBG), glucose and insulin tolerance tests were performed to assess glucose handling and development of hyperglycemia following 6‐week HFD (60% calories from fat). Mouse metabolic parameters were measured over 48 hours in Sable Promethion metabolic cages with ad libitum access to HFD. In male mice, PRR‐LoxP mice had significantly higher FBG when compared with the THPVN PRRKO mice (144.1 ± 5.74 vs. 121.9 ± 4.34 mg/dl, P= 0.0059) at the end of the six week HFD treatment. Interestingly, PRR ablation in the THPVN did not improve FBG and glucose handling in female mice. Metabolic cage measurements revealed that THPVN PRRKO mice had elevated oxygen consumption (VO2, ml/minute/g body weight) (0.047 ± 0.009 vs. 0.043 ± 0.0008 P= 0.027) and carbon dioxide emission (VCO2, ml/minute/g body weight) (0.035 ± 0.0005 vs. 0.032 ± 0.0005, P=0.0125) versus control HFD‐fed mice over 48 hours, indicating enhanced metabolic rate. The energy expenditure was significantly higher (0.0125 ± 0.00017 vs 0.0116 ± 0.00014, kCal/Hr/g body weight P=0.0026) in the THPVN PRRKO mice compared with their control counterparts. Locomotor activity over 48 hours was similar between the two groups (59.94 ± 19.6 vs. 103.5 ± 42.42 total meters traveled, P=0.204), and no significant difference in food intake (0.254 ± 0.011 vs. 0.274 ± 0.012 g, P=0.090) or body weight (42.7 ± 3.65 vs. 43.6 ± 1.41 g, P=0.842) was observed. This data suggests that PRR knockout in THPVN neurons protects against glucose dysregulation and elevates energy expenditure in mice following HFD. We conclude that PRR THPVN neurons play a key regulatory role in glucose and metabolic regulation.