Abstract WP16: Characterizing Cd38 Expression And Activity In The Brain Of Spontaneously Hypertensive Stroke Prone Rats

Abstract

Introduction: CD38 is an ectoenzyme that is the main source of age dependent decrease in NAD + levels. Its role in cerebral small vessel disease (cSVD) is unknown. We hypothesize that CD38 is over-expressed and activated in spontaneously hypertensive stroke-prone rat (SHRSP), a model of human cSVD. Methods: 20 SHRSP and 20 age matched male Wistar Kyoto control rats (WKY) were studied. Systolic blood pressure (SBP) was measured weekly using tail-cuff plethysmography. Half of the groups were euthanized at 7 weeks of age (Wks) and the remaining rats were followed until 24 Wks. Routine histology and immunohistochemistry (IHC) were performed for nitric oxide synthase (NOS) subtypes, superoxides (DHE), NO (DAF), and NADPH. IHC was used to detect CD38 expression and co-staining determined expression on endothelial cells (eNOS), astrocytes (GFAP), microglia (Iba1), T cells (CD3), macrophages (CD68), neutrophils (MPO) and neurons (Neuon). CD38 activity was detected in the brain homogenate by using a substrate analog of NAD + with measurement of its conversion to the strongly fluorescent product (ε-ADPR). Results: Compared to WKY, SHRSP developed hypertension between (9 -12) Wks and sustained it afterwards (SBP: 19 Wks: WKY 142.5±11.8 mmHg vs SHRSP 180.3±12.8 mmHg, P<0.0001). At 24 Wks, SHRSP showed histological evidence of cSVD including microbleed, enlarged perivascular spaces, and lipohyalinosis. Compared to WKY, CD38 expression was increased in SHRSP brain (7 Wks: 102.6%, P=0.011, 24 Wks: 83.2%, p=0.0077). CD38 activity was also significantly higher in SHRSP (7 Wks: 11.8%, p=0.012, 24 Wks: 20.2%, p=0.0065). We identified CD38 expression on endothelial cells, astrocytes and microglia. In comparison to WKY, SHRSP showed lower levels of NADPH (7 Wks: 22.3%, p=0.029, 24 Wks: 65.5%, p=0.0065), NO (7 Wks: 39.3% p=0.0008, 24 Wks: 36%, p=0.04), endothelial NOS (7 Wks: 57.5%, p=0.02, 24 Wks: 50.6%, p=0.01) and higher superoxide (7 Wks: 131%, p<0.0001, 24 Wks: 163%, p<0.0001). Conclusions: The brain of SHRSP shows evidence for elevated CD38 activity and expression with associated oxidative stress, depletion of NADPH and eNOS dysfunction compared to normotensive WKY. These results suggest the potential role of CD38 based therapeutics in future management of human cSVD.