Cigarette smoke (CS) is the most preventable cause of death and chronic disease in the United States. In addition to being a risk factor for atherosclerosis and cancer, recent epidemiologic studies suggest that cigarette smoke promotes the progression of kidney disease.
The mechanisms by which cigarette smoke may accelerate some types of chronic kidney disease are currently unknown. A new study, being published by the American Physiological Society, demonstrates for the first time that human mesangial cells (MC) – cells in the blood vessels of the kidneys – are endowed with nicotinic receptors (nAChRs) α4, α5, α7, β2, β3, β4 and β5 (cells that interact with the nicotine in tobacco) and may play an active role in the development of certain kidney diseases.
The study, “Nicotine: The Link Between Cigarette Smoking and the Progression of Renal Injury?,” was conducted by Edgar A. Jaimes, MD, Run-Xia Tian, MD, and Leopoldo Raij, MD, all of the Miller School of Medicine, University of Miami, Miami, FL. It appears in the Articles in Press Section of the American Journal of Physiology – Heart and Circulatory Physiology (http://ajpheart.physiology.org/), one of 11-peer reviewed journals published by the APS.
Overview of Methodology
Human mesangial cells were grown in CSC-Complete media, supplemented with 10 percent fetal calf serum. Cells were passed by trypsinization when confluent and used between the third and ninth passages. 3H-thymidine was used as an index of cell proliferation and cells were fasted for 72 hours in Maintenance Media and stimulated for 24 hours with nicotine (10-10 M to 10-7 M) or platelet derived growth factor.
Western blots were performed after the cells fasted and had been stimulated for 24 hours with nicotine (10-7). Cell homogenates were washed and thereafter centrifuged for 30 minutes. Blots were incubated overnight with one of nine antibodies, which included mouse anti-α2-nAChR mAb’s, anti-α3-nAChR mAb’s, or anti-α4-nAChR mAb’s. Fibronectin mRNA expression was determined by real time PCR and protein expression was measured by western blot. Flow cytometry measurement was generated for reactive oxygen species.
Data were expressed as mean ± SEM. For statistical comparisons involving two groups, an unpaired Student t test was used. For comparisons involving more than two groups, ANOVA was used. Significance was considered when P<0.05.
Highlights of Results
Highlights of the results include the following:
Human mesangial cells express nAChRs: The researchers were able to detect strong expression of several nAChRs subunits in the cultured human mesangial cells. They detected the presence of the nAChRs subunits α4, α5, α7, β2, β3, and β4 in these cells. They were not, however, able to detect significant expression of the α2 or α3 nAChR subunits.
Nicotine increases mesangial cell proliferation via nAChRs activation: Nicotine stimulation of the cells resulted in a dose dependent increase in mesangial cell proliferation. One concentration found in the plasma of active smokers found that nicotine-induced MC proliferation was 1,328 for controls vs. 2,761 for nicotine.
Nicotine increases fibronectin production: To determine whether transcriptional mechanisms were involved, the researchers measured the gene expression of fibronectin using real time exposure to nicotine. They found that nicotine induced a five-fold increase in fibronectin mRNA expression.
Summary and Conclusions
These studies are believed to be the first of their kind to:
(1) identify the presence of functionally active nAChRs in human mesangial cells; and
(2) demonstrate that nicotine, at concentrations similar to those found in the plasma of smokers, promotes mesangial cell proliferation and spurs on critical molecules that are involved in the extracellular matrix production.
Recent epidemiologic studies demonstrate that cigarette smoking increases the risk for progressive chronic kidney disease, but the role of smoking in primary renal diseases is less known. The results of this research, coupled with earlier findings, reveal previously unrecognized mechanisms showing nicotine – a component of cigarette smoke – as an agent that may accelerate and promote the progression of chronic kidney disease.
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