Central Actions of the Chemokine Stromal Cell-Derived Factor-1 Contribute to Neurohumoral Excitation in Heart Failure Rats

Abstract

The ample expression of chemokines and their receptors by neurons in the brain suggests that they play a functional role beyond the coordination of inflammatory and immune responses. Growing evidence implicates brain chemokines in the regulation of neuronal activity and neurohormonal release. This study examined the potential role of brain chemokines in regulating hemodynamic, sympathetic and neuroendocrine mechanisms in rats with ischemia-induced heart failure (HF). Immunohistochemical analysis revealed that the chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 was highly expressed in the hypothalamic paraventricular (PVN) and subfornical organ, and that SDF-1 expression was significantly increased in HF rats compared with sham-operated (SHAM) control rats. Intracerebroventricular (ICV) injection of SDF-1 induced substantial and long-lasting increases in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in both SHAM and HF rats, but responses were exaggerated in HF rats. Bilateral microinjection of SDF-1 into the PVN also elicited exaggerated increases in BP, HR and RSNA in the HF rats. A 4-hour ICV infusion of SDF-1 increased plasma levels of arginine vasopressin (AVP), adrenocorticotropic hormone (ACTH) and norepinephrine (NE) in normal rats, responses that were prevented by pretreatment with ICV SDF-1 short-hairpin RNA (shRNA). ICV administration of SDF-1 shRNA also reduced plasma AVP, ACTH and NE levels in HF rats. These data suggest that the chemokine SDF-1, acting within the brain, plays an important role in regulating sympathetic drive, neuroendocrine release, and hemodynamic function in normal and pathophysiological conditions, and so may contribute to the neural and humoral activation in HF.

INTRODUCTION

Recent studies have identified numerous physiological and pathophysiological functions of chemokines, beyond their traditionally recognized role as chemo-attractants.¹ More than 50 chemokines and 20 chemokine receptors have been identified, and more than half of those are represented in the central nervous system (CNS).² Chemokines and their G protein-coupled receptors are constitutively expressed by astrocytes, microglia and neurons in physiological and pathological states.^{2, 3} Within the CNS, chemokines have been implicated in development, neuroinflammation, dendritic differentiation, synaptic transmission and neuroendocrine regulation.^{4, 5} They have been reported to regulate the electrical activity of neurons and the release of neurotransmitters and neuropeptides such as glutamate, γ-aminobutyric acid, dopamine, serotonin, opioids and cannabinoids.^{6, 7}

Of particular interest to our laboratory, which has previously demonstrated a significant contribution of central inflammation to sympathetic nerve activity in systolic heart failure (HF),^{8, 9} chemokines and their receptors are present in several key cardiovascular regulatory regions of the brain - the hypothalamic paraventricular nucleus (PVN), the supraoptic nucleus (SON), and the subfornical organ (SFO) – that have been implicated in the pathophysiology of HF. The present study was designed to determine whether chemokines in these brain regions contribute to neurohumoral activation in HF.

The chemokines are a large subfamily of the cytokines. Some are pro-inflammatory and some are anti-inflammatory in nature.^{10, 11} In view of their numbers, their receptor promiscuity and their pleiotropic actions, efforts to define the contribution of any one chemokine to an inflammatory state like HF– e.g., by blocking its effects - would seem futile. On the other hand, a reasonable indication of the central influence of a particular chemokine in HF might be determined by manipulating its levels in cardiovascular regions of the brain. For that purpose, we chose to study the effects of the pro-inflammatory chemokine, stromal cell-derived factor-1 (SDF-1)/CXCL12, a member of the CXC subfamily. SDF-1 has only one known receptor,¹² for which a selective antagonist is available, and is known to regulate the release of arginine vasopressin (AVP),⁵ a function of neurons found only in the PVN and SON. In support of this choice, our preliminary studies demonstrated the presence of SDF-1 and its CXCR4 receptor in neurons and glial cells of the PVN, SFO and SON.

METHODS

Animals

Adult male Sprague-Dawley rats, weighing 275-325g, were purchased from Harlan Sprague Dawley. The animals were housed in temperature controlled (23 ± 2° C) rooms in University of Iowa Animal Care Facility and fed rat chow ad libitum. All experimental procedures were approved by the University of Iowa Institutional Animal Care and Use Committee. The experimental protocols were conducted in accordance with the National Institutes of Health “Guide for the Care and Use of Laboratory Animals.”

HF and sham-operated (SHAM) rats were prepared as previously described.¹³ The experimental protocols below were conducted approximately 4 weeks following induction of HF or sham operation.

Experimental protocols

SDF-1 and CXCR4 expression in PVN and SFO

SHAM (n=6) and HF (n=6) rats were euthanized and transcardially perfused with heparinized saline followed by 4% paraformaldehyde in 0.01M PBS. The collected brains were cut into 16-micron coronal sections for immunofluorescent studies to examine the expression of SDF-1 and its receptor (CXCR4) in PVN and SFO.

Quantification of SDF-1 and CXCR4 in PVN and SFO

SHAM (n=6) and HF (n=6) rats were anesthetized with urethane and decapitated immediately. The brain tissues were rapidly removed and frozen in liquid nitrogen. The PVN (including some surrounding tissue) and the SFO were harvested to measure the protein level of SDF-1 and CXCR4 by Western blot.

Hemodynamic and sympathetic effects of SDF-1

SHAM (n=24) and HF (n=24) rats were anesthetized and prepared for electrophysiological and hemodynamic recordings to determine the effects of intracerebroventricular (ICV) administration (25 ng or 100 ng in 2 μl) or bilateral PVN microinjection (2.5 ng or 5 ng in 0.2 μl in each side) of SDF-1 on renal sympathetic nerve activity (RSNA), blood pressure (BP), and heart rate (HR). SDF-1 for ICV injection or direct PVN microinjection was dissolved in artificial cerebrospinal fluid (aCSF), which served as vehicle (VEH).

Neuroendocrine effects of SDF-1

Neuroendocrine effects of SDF-1 were assessed in the following treatment groups.

• SHAM (n=6) and HF (n=6) rats treated with ICV vehicle (10 μl /hour for 4 hours);

• Normal rats pretreated 1 week earlier with ICV SDF-1 short-hairpin RNA (shRNA) lentiviral particles (n=6) or a scrambled shRNA (n=6) and then treated with ICV SDF-1 (50 ng/10μl/hour for 4 hours);

• HF rats pretreated 1 week earlier with ICV SDF-1 shRNA lentiviral particles (n=6) or a scrambled shRNA (n=5).

Rats were euthanized to collect trunk blood samples into EDTA tubes for ELISA assay of AVP, adrenocorticotropic hormone (ACTH) and norepinephrine (NE, as an indicator of sympathetic activation). Hemodynamic and molecular variables were also measured in the shRNA groups.

Specific Materials and Methods

Specific materials and methods are available in the online data supplement (http://hyper.ahajournals.org).

Statistical Analysis

The significance of differences among groups was analyzed by 2-way repeated-measure ANOVA followed by post hoc Fisher's test. For other unpaired data, a Student's t-test was used for comparison between groups. p< 0.05 was considered to indicate statistical significance.

RESULTS

Echocardiographic assessment of heart failure

The HF animals assigned to each group were well-matched with regard to echocardiographically defined left ventricular (LV) systolic function. The estimated size of the ischemic zone (%IZ) and the LV ejection fraction (LVEF) were not different in HF rats assigned to the different treatment groups. Only animals with large infarctions (% IZ >35 %) were used in this study. Compared with SHAM rats, LV end-diastolic volume was increased and LVEF was reduced in the HF rats. (Table S1)

SDF-1 and CXCR4 expression in PVN and SFO

Immunofluorescent studies revealed intense expression of SDF-1 immunoreactivity in PVN and SFO (Figure 1) of both SHAM and HF rats. In PVN, SDF-1 was expressed in all four commonly recognized subdivisions:¹⁴ the dorsal parvocellular (PVN-dp), the ventrolateral parvocellular (PVN-vlp), the medial parvocellular (PVN-mp) and the posterior magnocellular (PVN-pm). The PVN-vlp and PVN-pm had higher densities of SDF-1-like immunoreactivity than PVN-dp and PVN-mp in both SHAM and HF rats. In SFO, SDF-1 was evenly expressed throughout the nucleus. In HF rats, compared with SHAM, SDF-1-like immunoreactivity was more intense (HF vs SHAM, p<0.05) in both PVN and SFO (Figure 1A and 1C). The Western blot analysis confirmed a substantially higher (p<0.05) expression of the SDF-1 in the PVN (Figure 2A) and SFO (Figure 2C) of HF rats compared with SHAM.

Figure 1.

Laser confocal images showing expression of chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 (A) and its receptors CXCR4 (B) in PVN and SFO of SHAM and HF rats. Green: SDF-1 or CXCR4; Red: neuronal marker NeuN; Yellow: Merged. Scale bar: 0.2 mm in PVN; 0.5 mm in SFO. (C) Quantification of SDF-1 and its receptor CXCR4 immunoreactivity in PVN and SFO in SHAM and HF rats. dp, dorsal parvocellular; vlp, ventrolateral parvocellular; mp, medial parvocellular; pm, posterior magnocellular. Values are expressed as means ± SEM of the immunofluorescent intensity in arbitrary units (AU; n=6 for each group). * p<0.05 compared to SHAM rats.

Figure 2.

Western blot analysis showing the expression of SDF-1/CXCL12 and CXCR4 in the PVN (A and B) and SFO (C and D) in HF and the SHAM rats. 6 animals in each group. Values are expressed as means ± SEM and normalized to β-actin. * p<0.05, compared to SHAM.

Confocal immunofluorescent images indicated that SDF-1 receptor CXCR4 was abundantly expressed in both PVN and SFO. However, in contrast to its ligand, CXCR4 immunofluorescent reactivity was not increased in the PVN and SFO of HF rats, compared with SHAM (Figure 1B and 1C). Similarly, Western blot revealed no significant difference in the level of CXCR4 in PVN (Figure 2B) and SFO (Figure 2D) of HF rats compared with SHAM rats.

Cellular localization of SDF-1 and CXCR4

Both SDF-1 and CXCR4 were expressed in the neurons and glial cells in the PVN and SFO. Figure S1 shows the expression of SDF-1 and CXCR4 in PVN neurons and astrocytes, and Figure S2 shows SDF-1 in microglia of the PVN.

In the PVN, SDF-1 immunoreactivity co-localized with AVP immunoreactivity in neurons of the PVN-pm (Figure 3A) and with corticotrophin-releasing hormone (CRH) immunoreactivity in PVN-mp neurons (Figure 3B). Co-localization of SDF-1 with AVP or CRH expression was found in both SHAM and HF rats.

Figure 3.

Representative confocal images of the PVN, double-labeled for chemokine SDF-1 (green) and AVP (red, A) or CRH (red, B). Left panel in A or B: low-power views from a HF rat, showing the full expanse of PVN (unilateral, third ventricle to the left). Right three panels in A or B: High-power views taken from the posterior magnocellular subdivision or medial parvocellular subdivision of PVN of the HF rat, in the regions indicated by the yellow rectangles. The merged images show the co-localization (yellow) of SDF-1 with AVP (A) or CRH (B) immunoreactivity.

Hemodynamic and sympathetic effects of SDF-1

In SHAM rats (n=6), ICV injection of SDF-1 at the dose of 25 ng had no effect on MBP, HR and RSNA (Figure 4A and 4E). In HF rats (n=6, Figure 4C and 4E), however, the same dose of SDF-1 increased MBP (from 95.2 ± 3.1 to 112.3 ± 3.7 mmHg), HR (321 ± 10 to 359 ± 9 bpm) and RSNA (54.2± 6.5% change in integrated RSNA from a baseline of 20.3 ± 2.4 mV), measured at 3 hours. The 100 ng ICV dose of SDF-1 induced an increase in MBP, HR and RSNA in the SHAM rats (n=6, Figure 4B) and an even larger increase in the HF rats (n=6, Figure 4D and 4E). The responses to SDF-1 began within 20 minutes of the ICV injection, peaked at 3-5 hours and lasted for 8-10 hours and even longer in most cases. ICV injections of an equal volume of vehicle (aCSF) did not cause obvious changes on BP, HR and RSNA in either SHAM (n=4) or HF (n=4) rats (data not shown).

Figure 4.

Representative tracings showing the effects of ICV SDF-1/CXCL12 on BP, HR and RSNA in SHAM (A, B) and HF rats (C, D). (E), Grouped data showing the changes from baseline in MBP (mmHg), HR (bpm) and RSNA (%) elicited by ICV SDF-1 in SHAM and HF rats, BP: blood pressure; MBP: mean blood pressure; HR: heart rate; RSNA: renal sympathetic nerve activity, windowed (spikes/s) and integrated (mV). The integrated RSNA was used for data analysis. Scale bar: 20 min. Values are expressed as means ± SEM. * p<0.05, 100 ng vs. 25 ng dose in either HF or SHAM. † p<0.05, HF vs. SHAM at the 100 ng or 25 ng dose.

PVN microinjections of SDF-1 elicited similar dose-dependent responses. Bilateral PVN microinjection of 2.5 ng of SDF-1 had no obvious effect on MBP, HR and RSNA in SHAM rats, but increased MBP (88.8 ± 3.0 to 95.6 ± 3.1 mmHg), HR (334 ± 7 to 352 ± 8 bpm) and RSNA (20.8 ± 3.0 % change in integrated RSNA, from a baseline of 19.4 ± 2.1 mV) in HF rats (n=6, figure 5A, C). Bilateral PVN microinjection of 5 ng of SDF-1 increased MBP (99.8 ± 2.9 to 107.5 ± 3.1 mmHg), HR (306 ± 7 to 327 ± 8 bpm ) and RSNA (24.1± 2.4 % change in integrated RSNA, from a baseline of 11.7 ± 2.0 mV) in SHAM rats, and even greater increases in MBP (from 89.5 ± 2.5 to 100.1±2.7 mmHg), HR (332 ± 8 to 360 ± 9 bpm) and RSNA (35.1±4.2 % change in integrated RSNA, from a baseline of 21.4±2.9 mV) in HF rats, measured at 2 hours (n=6, Figure 5B,D). The responses to SDF-1 began within 10 minutes after PVN microinjection and were sustained for 3-5 hours in SHAM and HF rats. Bilateral PVN microinjection of an equal volume of vehicle (aCSF) did not elicit responses on BP, HR and RSNA in either SHAM (n=5) or HF (n=5) rats (Figure S7).

Figure 5.

Representative tracings showing the effects of bilateral PVN microinjection of SDF-1 on BP, HR and RSNA in SHAM (A, B) and HF rats (C, D). (E), Grouped data showing the changes from baseline in MBP (mmHg), HR (bpm) and RSNA (%) elicited by PVN microinjection of SDF-1 in SHAM and HF rats. The integrated RSNA was used for data analysis. Scale bar: 20 min. Values are expressed as means ± SEM. * p<0.05, 5 ng vs. 2.5 ng dose in either HF or SHAM. † p<0.05, HF vs. SHAM at the 5 ng or 2.5 ng dose.

Neuroendocrine effects of SDF-1

In HF rats treated with ICV vehicle (n=6), the plasma levels of AVP (Figure 6A), ACTH (Figure 6B) and NE (Figure 6C) were 2-3 times higher compared with ICV vehicle-treated SHAM rats (n=6). In HF rats pretreated a week earlier with ICV SDF-1 shRNA, plasma AVP, ACTH and NE levels were significantly lower compared with the HF rats treated with a scrambled shRNA control (n=5, Figure 6). The MBP of HF rats pretreated with SDF-1 shRNA was not significantly different from that of HF rats treated with the control shRNA (92.1± 3.8 vs. 87.3 ± 3.6 mmHg), but HR was significantly lower (316 ± 8 vs. 342 ± 7 bpm, p<0.05).

Figure 6.

Plasma AVP (A), ACTH (B) and NE (C) in SHAM or HF rats treated with ICV vehicle, normal rats treated with a 4-hour ICV infusion of SDF-1 one week after pretreatment with SDF-1 shRNA or a control shRNA, and HF rats treated with SDF-1 shRNA or control shRNA. Values are expressed as means ± SEM. * p<0.05, vs. SHAM + VEH. † p<0.05, HF + SDF-1 shRNA vs HF + Control shRNA. # p<0.05, Normal + SDF-1 shRNA + SDF-1 vs Normal + Control shRNA + SDF-1.

In normal rats pretreated with a scrambled control shRNA, a 4-hour ICV infusion of SDF-1 (50 ng/hour, n=6) significantly augmented the plasma levels of AVP, ACTH and NE, effects which were prevented by pretreatment one week earlier with ICV shRNA for SDF-1 (n=6, Figure 6). The SDF-1 shRNA pretreatment markedly attenuated ICV SDF-1 (50 ng/hour, n=6) - induced increases in MBP (11.2 ± 2.3 vs. 27.4 ± 4.5 mmHg, p<0.01) and HR (23 ± 5 vs. 72 ± 10 bpm, p<0.01), compared with pretreatment with control shRNA.

The efficacy of the SDF-1 shRNA lentiviral particles was confirmed by western blot analysis, using the brain tissues from the HF groups tested for neuroendocrine and hemodynamic effects of ICV SDF-1 shRNA or control shRNA. One week after ICV injection of the lentiviral particles, the HF rats treated with SDF-1 shRNA had significantly lower levels of SDF-1 protein in PVN and SFO than the HF rats treated with the scrambled shRNA control (Figure S5).

DISCUSSION

This study provides the first evidence to suggest that brain chemokines contribute to the regulation of cardiovascular function, sympathetic outflow and neuroendocrine release in systolic HF. The novel findings of this study are: 1) in rats with ischemia-induced HF, expression of the chemokine SDF-1 is upregulated in PVN and SFO, key cardiovascular regulatory regions of the forebrain; 2) HF rats have an exaggerated sympathetic response to ICV injection of SDF-1 or bilateral microinjection of SDF-1 into the PVN; 3) SDF-1 co-localizes with neuroendocrine (AVP and CRH) neurons in the PVN; 4) treatment with SDF-1 increases plasma AVP, ACTH and NE levels in normal rats; 5) shRNA to reduce endogenous SDF-1 expression in the brain reduces plasma AVP, ACTH and NE in HF rats, and attenuates the neuroendocrine responses to ICV SDF-1 in normal rats. SDF-1 and its CXCR4 receptor are expressed in microglia, astrocytes and neurons of the PVN and SFO. Taken together, these findings strongly suggest that brain chemokines contribute to neural and humoral excitation in HF.

Although not tested in this study, it seems likely that the overexpression of pro-inflammatory cytokines in the brain in this model of HF ¹⁵ promotes an overexpression of chemokines. The pro-inflammatory cytokines stimulate glial cells to produce chemokines in vitro,¹⁶ and we have found that an ICV injection of the pro-inflammatory cytokine tumor necrosis factor – alpha increases the expression of SDF-1 in the PVN and SFO in normal rats.¹⁷ Other factors that are increased in the brain in HF and have been reported to induce SDF-1 expression in the periphery,^{18, 19} including reactive oxygen species, angiotensin II and aldosterone, may also stimulate chemokine production in the brain.

ICV injection of SDF-1 elicited an exaggerated response in the HF rats, compared with SHAM, in the absence of increased numbers of CXCR4 receptors in the PVN or SFO. This finding suggests that the higher intrinsic levels of SDF-1 in PVN and SFO of HF rats, shown by immunofluorescence and confirmed by Western blot, render an otherwise subthreshold dose of exogenous SDF-1 sufficient to elicit a sympatho-excitatory response. This interpretation is supported by the findings in normal rats pretreated with shRNA for SDF-1, demonstrating that reducing the basal SDF-1 expression prevented the humoral response and reduced the hemodynamic response to the higher ICV dose of SDF-1.

Humoral factors play an important role in HF. Vasopressin is believed to contribute to the volume accumulation and hyponatremia that are prominent findings in severe systolic heart failure.²⁰ Previous work from our lab has shown activation of PVN CRH neurons in this model of heart failure.²¹ CRH neurons are a marker of activation of the hypothalamic-pituitary-adrenal axis, with release of ACTH and activation of the sympathetic nervous system. The present study demonstrates co-localization of SDF-1 with AVP and CRH containing PVN neurons, upregulated expression of SDF-1 in HF rats, and a reduction in AVP and ACTH release in normal and HF rats when SDF-1 is targeted with shRNA. Taken together, these findings suggest that brain chemokines may contribute to the high circulating levels of neuroactive hormones found in this pathophysiological condition.

How exactly SDF-1 elicits sympathetic and neuroendocrine responses remains to be determined. SDF-1 may have both direct influences on the membrane potential of presympathetic or/and neuroendocrine neurons as well as indirect influences.⁶ SDF-1 is known to activate mitogen-activated protein kinase (MAPK) intracellular signaling pathways²² which we have found to have an important role in sympathetic activation in HF.²³ SDF-1 may be one of several excitatory mediators utilizing MAPK as a common signaling pathway. Additionally, chemokines can activate glial cells to produce cyclooxygenase-2 (COX₂) and prostaglandin-E2 (PGE₂),²⁴ which is sympatho-excitatory in the central nervous system. In preliminary studies, we have found that central administration of SDF-1 increased the expression of COX₂ in the PVN. The long duration of the SDF-1 effects suggests the possibility of genomic influences in addition to synaptic and cellular mechanisms.

Finally, it is important to consider the potential sources of SDF-1 and other chemokines in pathophysiological states. Chemokines and their receptors are abundantly expressed in glial cells,²⁵ which have recently been implicated in activation of the sympathetic nervous system in hypertension²⁶ and heart failure.²⁷ In preliminary studies, we have found that SDF-1 is expressed in astrocytes (Figure S1) and microglia (Figure S2) in the HF rats, suggesting that glial cells may contribute substantially to chemokine-mediated neurohumoral excitation in that condition.

Limitations of the study

In preliminary experiments in SHAM and HF rats, ICV administration of the CXCR4 antagonist AMD 3100 over a wide range of doses failed to block the hemodynamic and sympathetic responses to ICV SDF-1, and in fact elicited a paradoxical pressor response (see Figure S6). As a result, we were unable to establish CXCR4 as the only receptor mediating the cardiovascular and sympathetic responses to SDF-1. Others have reported that AMD 3100 was not effective in blocking the excitatory effects of SDF-1 on melanin-concentrating hormone neurons in the lateral hypothalamic area.²⁸ Those findings and ours suggest the possibility that the excitatory effects of SDF-1 may be mediated by an alternate receptor. Notable in that regard is a recent report that SDF-1 binds to an orphan G protein receptor called CXCR7 in T lymphocytes.²⁹ An important and confounding implication for future studies is that AMD 3100 may not be helpful in determining the role of SDF-1 in pathophysiological states like heart failure and hypertension. Nevertheless, in the present study HF rats were clearly more sensitive to the effects of SDF-1 on sympathetic excitation, and shRNA for SDF-1 did reduce the plasma levels of AVP, ACTH and NE in HF rats and normal rats infused with SDF-1. These are convincing indications of the pathophysiological impact of pro-inflammatory chemokines in HF.

Finally, the immunohistochemical and microinjection data in this study identify the PVN as one central site at which SDF-1 can act to augment sympathetic drive and neuroendocrine release, but not as the only or even the primary site of SDF-1 action in pathophysiological states. SDF-1 is also expressed and upregulated in SFO in HF rats, and our limited preliminary studies indicate that it is amply expressed in SON (Figure S3) and RVLM (Figure S4) as well. All of these cardiovascular and autonomic regions are involved in neurohumoral regulation, and the interventions employed in this study do not discriminate among them. Further work will be required to determine the predominant central site or sites of action of SDF-1.

Perspectives

The data presented here are the first evidence suggesting a potential role for brain chemokines in the regulation of autonomic function in HF. Though this study focused on the chemokine SDF-1, other chemokines are likely also involved. The significant effects on sympathetic drive, hemodynamic responses and neuroendocrine release induced by ICV SDF-1 make a strong argument for chemokine regulation of autonomic and cardiovascular function in normal and pathophysiological conditions and suggest that brain chemokines, like the pro-inflammatory cytokines and the brain renin-angiotensin system, play an important role in the pathogenesis of HF. It may be that chemokines mediate the responses to pro-inflammatory cytokines, which can stimulate chemokine production,^{16, 17} in key brain regions like the PVN in which cytokine receptors appear to be relatively sparsely represented^{30, 31} but chemokine receptors are abundant.⁵ Further studies probing the role of brain chemokines will provide a better understanding of inflammatory mechanisms in HF, and may lead to improvements in pharmaceutical treatment of this devastating disease.

In addition to its relevance to cardiovascular diseases like HF and hypertension, this work opens new territory for the investigation of biological functions of chemokines in metabolic diseases like diabetes and obesity, in which inflammatory mediators are also critical contributing factors leading to neurohumoral and sympathetic activation.

Novelty and Significance.

1. What Is New?

   • Expression of the chemokine SDF-1 is upregulated in key cardiovascular autonomic regions of the brain in rats with heart failure
   • Centrally administered SDF-1 induces sympathetic and neuroendocrine responses that are exaggerated in rats with heart failure.
2. What Is Relevant?

   • Inflammation in the brain contributes importantly to the pathophysiology of hypertension and heart failure.
   • This study identifies a previously unappreciated role for brain chemokines as mediators of the neurohumoral effects of central inflammation.
3. Summary

   • The chemokine SDF-1 acts within the central nervous system to regulate sympathetic and neuroendocrine activity, and may contribute to exaggerated neurohumoral activity in cardiovascular disease states like heart failure and hypertension.