Impaired ceramide signalling in spontaneously hypertensive rat vascular smooth muscle: a possible mechanism for augmented cell proliferation

Objectives In hypertension, the vascular wall undergoes morphological chang es that alter mechanical responses to vasoactive substances. Ceramide is a recently identified second messenger synthesized in response to cytokines s uch as tumour necrosis factor alpha (TNF-alpha), It has been previously dem onstrated that vascular smooth muscle cells (VSMC) from genetically hyperte nsive rats proliferate at a higher rate than those of normotensive origin. We tested the hypothesis that the ceramide pathway is impaired in VSMC from spontaneously hypertensive rats (SHR), Design VSMC were isolated from aortae of SHR and from Wistar-Kyoto (WKY) ra ts, Ceramide levels were measured under baseline and agonist-stimulated con ditions and cell proliferation was monitored. Methods Cell proliferation was determined by cell counting. Ceramide levels were determined via radioactive labelling, high-performance thin-layer chr omatography and phosphorimaging, Relative mRNA levels of neutral sphingomye linase were determined using semiquantitative polymerase chain reaction (PC R). Results Basal ceramide levels in untreated cells were lower in cells from S HR compared to WKY rats. During chronic treatment with TNF-alpha, ceramide levels increased in WKY rat cells but remained unchanged in cells from SHR. TNF-alpha treatment had an inhibitory effect on WKY rat VSMC proliferation , but stimulated proliferation in cells from SHR, Short-term incubation wit h TNF-alpha resulted in a greater increase in ceramide in cells from WKY ra ts than those from SHR. Semiquantitative PCR analysis indicated that neutra l sphingomyelinase mRNA may be reduced in SHR VSMC. Conclusions We conclude that ceramide synthesis is impaired in vascular smo oth muscle from SHR and may contribute to increased VSMC proliferation in h ypertension, (C) 2001 Lippincott Williams & Wilkins.