Vitamin D deficiency exacerbates ischemic cell loss and sensory motor dysfunction in an experimental stroke model Robyn Balden & Farida Sohrabji Texas A&M Health Science Center- College of Medicine ISC 2012
Vitamin D deficiency (VDD) and cardiovascular disease Cardiovascular disease (CVD), a chronic inflammatory condition, is associated with low Vitamin D levels A growing body of data suggests Vitamin D modifies the risk of CVD indirectly through chronic and inflammatory CV risk factors such as diabetes, dyslipidemia, and metabolic syndrome Vitamin D levels are independently associated with CV events including stroke and congestive heart failure Clinical studies indicate that Vitamin D levels are significantly lower in acute stroke patients vs. controls, and that low Vitamin D levels increase the risk for future strokes and are independently predictive for fatal strokes Because VDD is associated with a number of chronic inflammatory conditions including cancer, autoimmune, and CVD, the unique contribution of VDD to cardiovascular and cerebral ischemia is not clear These experiments specifically seek to determine the effects of Vitamin D deficiency on the severity of stroke
Vitamin D deficiency and the immune system Activated Vitamin D is known to act as an antiinflammatory immunomodulator capable of directly and indirectly regulating cytokine expression Vitamin D is a steroid hormone/nuclear transcription factor Vitamin D exerts direct effects on activation, phenotypic determinants, and secretions of T cells and antigen presenting cells By regulating cytokine and gene expression, Vitamin D suppresses development of Th1 and Th17 cells in favor of the Th2 and Treg subtypes
The post-stroke inflammatory response With age, disease, and inflammation, the overall function of the cardiovascular and immune systems suffer. Importantly, in ischemic stroke and reperfusion, the function of these systems is critical to CNS survival Inflammation contributes to stroke outcome: Following an ischemic insult, leukocytes are recruited into cerebral microcirculation and cytokines and growth factors accumulate at the site of injury We predict Vitamin D deficiency influences the response to injury, due to its known effects on the immune system and growth factor production *Selvamani, A. and F. Sohrabji 2010 Reproductive age modulates the impact of focal ischemia on the forebrain as well as the effects of estrogen treatment in female rats. Neurobiol Aging. 31(9): p. 1618-28.
Vitamin D deficient diet reduces circulating 25-OHD and 1,25-OH2D levels A. B. * * C. D. Cortex a,b Striatum a,b Cortex b Striatum
Cerebral ischemia results in a larger infarct in VDD rats A. 3 DAYS B. Control Vitamin D Deficient Control 5 DAYS Vitamin D Deficient C. D. 3 days Post-Stroke 5 days Post-Stroke a,b,c a,b,c
Post-stroke behavioral deficits are exacerbated by Vitamin D deficiency A. B. Left b Right a,b,c Left Right a,b Vitamin D deficient rats sustain greater deficits in sensorimotor behavioral tests
Post-stroke growth factor (IGF-1)expression is regulated by Vitamin D status A. B. C. Cortex b Striatum b Cortex a,b,c Striatum a,b,c D. E. * Growth factors contribute to CNS repair after stroke
Cytokine expression varies with Vitamin D status A. B. Cortex b,c Striatum b,c Cortex b Striatum b Ischemia-induced IL-6 expression positively correlates with infarct volume in the cortex and striatum Increased expression of IL-6 and TGF-β, a cytokine upregulated by ischemia, is known to suppress the development of protective Regulatory T cells (Tregs)
Treg activation is decreased in VDD ischemic brain tissue Treg Th17 Cells from the ischemic cortex were triple-labeled for CD4, CD25, and FoxP3. For brevity, the CD4+ populations are displayed above showing co-expression of Treg surface (CD25) and intracellular (FoxP3) markers. Quadrant 2 (Q2) contains triple-labeled cells. The Median Fluorescence Intensity (MFI) of triple-labeled cells is significantly higher in controls (8033+692) than Vitamin D deficient (2029+149) animals (p<0.05).
RORγ(t) Treg activation is decreased in VDD splenic tissue after ischemia Treg Th17 IL-17A The MFI of triple-labeled cells in Q2 is significantly higher in controls (1835+181) than Vitamin D deficient (1175+39) animals (p<0.05).
*von Essen, M.R., M. Kongsbak, P. Schjerling, K. Olgaard, N. Odum, and C. Geisler 2010 Vitamin D controls T cell antigen receptor signaling and activation of human T cells. Nat Immunol. 11(4): p. 344-9. Summary VDD diet effectively reduced plasma levels of Vitamin D Vitamin D deficiency exacerbates the detrimental impact of ischemia Cytokines and IGF-1 are differentially expressed in control versus VDD animals Treg cells are activated to a greater degree in controls as compared with Vitamin D deficient rats Inadequate circulating Vitamin D prevents initiation of appropriate immune responses. VDR and its ligand 1,25(OH)2D3, the active form of Vitamin D, are essential cofactors in naïve human T cell activation and expansion (von Essen et al. 2010, Nature Immunology*)
Questions? Robyn Balden & Farida Sohrabji Texas A&M Health Science Center- College of Medicine ISC 2012