Abstract 032: Afferent Renal Denervation And IL-1 Receptor Blockade Attenuate The Pathogenesis Of Hypertension In DOCA-salt Mice Similarly: Evidence For A Common Mechanism?

Emerging evidence suggests an interaction between renal inflammation and afferent renal nerves in some preclinical models of hypertension. In this study we tested the hypothesis that the inflammatory cytokine IL-1β interacts with afferent renal nerves in the pathogenesis of the DOCA-salt mouse model of hypertension. Specifically, we compared the effect of total renal denervation (TRDN) and afferent RDN (ARDN) on the development of DOCA-salt hypertension to that observed in animals receiving the IL-1 receptor antagonist anakinra. In the first study , 10-week-old male C57BL6/J mice were implanted with radiotelemeters for measurement of mean arterial pressure (MAP). DOCA was administered via subcutaneous pellet containing 50 mg of DOCA, controls received a drug free pellet. Uni-nephrectomy, pellet insertion, salt treatment, TRDN, ARDN, or sham denervation were all performed on the same day. TRDN and ARDN was performed through peri-axonal application of phenol and capsaicin respectively. In the second study , the IL-1 receptor antagonist anakinra (75mg/kg) or vehicle control (0.9% saline) was delivered via intraperitoneal injection daily 10 days post-induction of hypertension. Renal cytokine protein was quantified by Multiplex ELISA. All values reported are mean + SEM, all groups n=5. In the first study , MAP increased in sham treated DOCA-salt mice +43 ± 1 mmHg from baseline by the end of the 3 rd week of DOCA-salt. This response was attenuated by 40% in TRDN (+26 ± 4 mmHg) and by 44% in ARDN DOCA-salt mice (+24 ± 3 mmHg). IL-1β was increased in DOCA-salt kidneys (2.1 ± 0.4 pg/mg) compared to control kidneys (0.36 ± 0.1 pg/mg). In the second study , anakinra similarly attenuated the increase in MAP by 45% (+21 ± 2 mmHg) compared to vehicle controls (+38 ± 1 mmHg). Neither ARDN nor IL-1 receptor antagonism had any effect on renal inflammatory cytokines IL-1β, IL-6, or TNFα. The comparable attenuation in the MAP response to DOCA-salt ARDN and anakinra treated groups as well as the unchanged inflammatory phenotype is consistent with a common mechanism of action. We hypothesize that intrarenal IL-1β activates sympathoexcitatory renal afferent nerves to increase MAP in DOCA-salt mice. Future studies are needed to directly test this hypothesis.

Placental mTOR complex 1 regulates fetal programming of obesity and insulin resistance in mice

Fetal growth restriction, or low birth weight, is a strong determinant for eventual obesity and type 2 diabetes. Clinical studies suggest placental mechanistic target of rapamycin (mTOR) signaling regulates fetal birth weight and the metabolic health trajectory of the offspring. In the current study, we used a genetic model with loss of placental mTOR function (mTOR-KO^Placenta) to test the direct role of mTOR signaling on birth weight and metabolic health in the adult offspring. mTOR-KO^Placenta animals displayed reduced placental area and total weight, as well as fetal body weight at embryonic day (E) 17.5. Birth weight and serum insulin levels were reduced; however, β cell mass was normal in mTOR-KO^Placenta newborns. Adult mTOR-KO^Placenta offspring, under a metabolic high-fat challenge, displayed exacerbated obesity and metabolic dysfunction compared with littermate controls. Subsequently, we tested whether enhancing placental mTOR complex 1 (mTORC1) signaling, via genetic ablation of TSC2, in utero would improve glucose homeostasis in the offspring. Indeed, increased placental mTORC1 conferred protection from diet-induced obesity in the offspring. In conclusion, placental mTORC1 serves as a mechanistic link between placental function and programming of obesity and insulin resistance in the adult offspring.

Targeted afferent renal denervation reduces arterial pressure but not renal inflammation in established DOCA-salt hypertension in the rat

Recent preclinical studies show renal denervation (RDNx) may be an effective treatment for hypertension; however, the mechanism remains unknown. We have recently reported total RDNx (TRDNx) and afferent-selective RDNx (ARDNx) similarly attenuated the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Whereas TRDNx abolished renal inflammation, ARDNx had a minimal effect despite an identical antihypertensive effect. Although this study established that ARDNx attenuates the development of DOCA-salt hypertension, it is unknown whether this mechanism remains operative once hypertension is established. The current study tested the hypothesis that TRDNx and ARDNx would similarly decrease mean arterial pressure (MAP) in the DOCA-salt hypertensive rat, and only TRDNx would mitigate renal inflammation. After 21 days of DOCA-salt treatment, male Sprague-Dawley rats underwent TRDNx ( n = 16), ARDNx ( n = 16), or Sham ( n = 14) treatment and were monitored for 14 days. Compared with baseline, TRDNx and ARDNx decreased MAP similarly (TRDNx -14 ± 4 and ARDNx -15 ± 6 mmHg). After analysis of diurnal rhythm, rhythm-adjusted mean and amplitude of night/day cycle were also reduced in TRDNx and ARDNx groups compared with Sham. Notably, no change in renal inflammation, injury, or function was detected with either treatment. We conclude from these findings that: 1) RDNx mitigates established DOCA-salt hypertension; 2) the MAP responses to RDNx are primarily mediated by ablation of afferent renal nerves; and 3) renal nerves do not contribute to the maintenance of renal inflammation in DOCA-salt hypertension.

Serine racemase is expressed in islets and contributes to the regulation of glucose homeostasis

NMDA receptors (NMDARs) have recently been discovered as functional regulators of pancreatic β-cell insulin secretion. While these excitatory receptor channels have been extensively studied in the brain for their role in synaptic plasticity and development, little is known about how they work in β-cells. In neuronal cells, NMDAR activation requires the simultaneous binding of glutamate and a rate-limiting co-agonist, such as D-serine. D-serine levels and availability in most of the brain rely on endogenous synthesis by the enzyme serine racemase (Srr). Srr transcripts have been reported in human and mouse islets but it is not clear whether Srr is functionally expressed in β-cells or what its role in the pancreas might be. In this investigation, we reveal that Srr protein is highly expressed in primary human and mouse β-cells. Mice with whole body deletion of Srr (Srr KO) show improved glucose tolerance through enhanced insulin secretory capacity, possibly through Srr-mediated alterations in islet NMDAR expression and function. We observed elevated insulin sensitivity in some animals, suggesting Srr metabolic regulation in other peripheral organs as well. Srr expression in neonatal and embryonic islets, and adult deficits in Srr KO pancreas weight and islet insulin content, point toward a potential role for Srr in pancreatic development. These data reveal the first evidence that Srr may regulate glucose homeostasis in peripheral tissues and provide circumstantial evidence that D-serine may be an endogenous islet NMDAR co-agonist in β-cells.