Abstract-Remodeling of small arteries is essential in the long-term regulation of blood pressure and blood flow to specific organs or tissues. A large part of the change in vessel diameter may occur through non-growth-related reorganization of vessel wall components. The hypothesis was tested that tissue-type transglutaminase (tTG), a cross-linking enzyme, contributes to the inward remodeling of small arteries. The in vivo inward remodeling of rat mesenteric arteries, induced by low blood flow, was attenuated by inhibition of tTG. Rat skeletal muscle arteries expressed tTG, as identified by Western blot and immunostaining. In vitro, activation of these arteries with endothelin-1 resulted in inward remodeling, which was blocked by tTG inhibitors. Small arteries obtained from rats and pigs both showed inward remodeling after exposure to exogenous transglutaminase, which was inhibited by addition of a nitric oxide donor. Enhanced expression of tTG, induced by retinoic acid, increased inward remodeling of porcine coronary arteries kept in organ culture for 3 days. The activity of tTG was dependent on pressure. Inhibition of tTG reversed remodeling, causing a substantial increase in vessel diameter. In a collagen gel contraction assay, tTG determined the compaction of collagen by smooth muscle cells. Collectively, these data show that small artery remodeling associated with chronic vasoconstriction depends on tissue-type transglutaminase. This mechanism may reveal a novel therapeutic target for pathologies associated with inward remodeling of the resistance arteries. hronic alteration in the hemodynamic profile is associated with arterial remodeling. Both large and small arteries adapt to a reduction in blood flow with a decrease in lumen diameter, 1,2 and in several forms of hypertension, the wall-to-lumen ratio of arteries is increased. 3,4 Although hypertrophy of the vessel wall may contribute to this remodeling in larger arteries, in resistance arteries, it mainly involves a geometrical reorganization of wall components around a smaller lumen. 5 Thus, in essential hypertension, the reduction in lumen size of resistance arteries appears to be eutrophic, ie, without a change in the amount of wall material. 3 In the process of inward remodeling, the reorganization of smooth muscle cells, induced by chronic vasoconstriction, may be an early event. 6 Whereas inward remodeling is identified as an important risk factor for cardiovascular events, 7 the mechanisms that control blood vessel caliber under physiological and pathological conditions are incompletely understood.Tissue-type transglutaminase (tTG), also called transglutaminase type 2, belongs to a family of enzymes that includes coagulation factor XIII. tTG is ubiquitously expressed and present both within the cells and at the cell surface, where it associates with integrins. 8 The enzyme catalyzes the formation of an N⑀ (␥-glutamyl)lysine cross-link, a bond between a glutamine residue and the primary amino group of either a peptide-bound lysine or a polyamine. M...

Abstract-To obtain information on the molecular and cellular mechanisms of flow-induced arterial remodeling, we analyzed the morphology and smooth muscle cell (SMC) characteristics in rat mesenteric resistance arteries after interventions that decreased and increased flow. Juvenile male Wistar Kyoto rats were subjected to surgery that, compared with control arteries, provided arteries with chronic low flow and chronic high flow. Low flow resulted in a decreased passive lumen diameter, hypotrophy of the artery wall, and both loss and decreased size of SMCs. Time course studies, with intervention length ranging from 2 to 32 days of altered blood flow, showed that the narrowing of the lumen diameter in low-flow arteries appeared within 2 days and that an early dedifferentiation of SMC phenotype was indicated by markedly reduced levels of desmin mRNA. High flow resulted in an increased passive lumen diameter and in hypertrophy of the artery wall. The hypertrophy resulted from SMC proliferation because SMC number, measured by the 3D-dissector technique, was increased and immunohistochemical assessment of proliferating cell nuclear antigen also showed an increase. The widening of high-flow arteries required 16 days to become established, at which time desmin mRNA was reduced. This time was also required to establish changed wall mass in both low-flow and high-flow arteries. Apoptotic cells detected by TdT-mediated dUTP-biotin nick end labeling staining were mainly located in the medial layer, and evaluation of DNA fragmentation indicated that increased apoptosis occurred in both low flow and high flow. This study shows for the first time direct evidence that reduced and elevated blood flow in resistance arteries produce, respectively, decrease and increase in SMC number, with dedifferentiation of the SMCs in both cases.

Remodeling of resistance arteries is a key feature in hypertension. We studied the transition of vasoconstriction to remodeling in isolated rat skeletal muscle arterioles. Arterioles activated with 10 nM endothelin-1 showed functional adaptation when kept at low distension in a wire myograph setup, where contractile properties shifted towards a smaller lumen diameter after 1 day. Pressurized arteries kept in organoid culture showed physical inward remodeling after 3-day activation with 10 nM endothelin-1, characterized by a reduction in relaxed diameter without a change in the wall cross-sectional area (eutrophic remodeling). The relaxed lumen diameter (at 60 mm Hg) decreased from 169 ± 5 (day 0) to 155 ± 4 µm (day 3). An antibody directed to the β₃-integrin subunit (but not one directed to the β₁-integrin subunit) enhanced remodeling, from a reduction in relaxed diameter at 60 mm Hg of 15 ± 2.4 to 22 ± 1.8 µm (both on day 3). Collagen gel contraction experiments showed that the antibody directed to the β₃-integrin subunit enhanced the compaction of collagen by smooth muscle cells, from 83 ± 1.5 to 68 ± 1.5% of the initial gel diameter. In conclusion, these data show that inward eutrophic remodeling is a response to sustained contraction, which may involve collagen reorganization through β₃-integrins.

Mechanisms of Ca2+ sensitization of force production by noradrenaline were investigated by measuring contractile responses, intracellular Ca2+ concentration ([Ca2+]i) and phosphorylation of the myosin light chain (MLC) in intact and α‐toxin‐permeabilized rat mesenteric small arteries. The effects of noradrenaline were investigated at constant membrane potential by comparing fully depolarized intact arteries in the absence and presence of noradrenaline. Contractile responses to K‐PSS (125 mM K+) and NA‐K‐PSS (K‐PSS + 10 μM noradrenaline) were titrated to 30 and 75 %, respectively, of control force, by adjusting extracellular Ca2+ ([Ca2+]o). At both force levels, [Ca2+]i was substantially lower with NA‐K‐PSS than with K‐PSS. With K‐PSS, the proportion of MLC phosphorylated (≈30 %) was similar at 30 and 75 % of control force; with NA‐K‐PSS, MLC phosphorylation was greater at the higher force level (40 vs. 34 %). In α‐toxin‐permeabilized arteries, the force response to 1 μM Ca2+ was increased by 10 μM noradrenaline, and MLC phosphorylation was increased from 35 to 45 %. The protein kinase C (PKC) inhibitor calphostin C (100 nM) abolished the noradrenaline‐induced increase in MLC phosphorylation and contractile response, without affecting the contraction in response to Ca2+. Treatment with ATPγS in the presence of the MLC kinase inhibitor ML‐9 increased the sensitivity to Ca2+ and abolished the response to noradrenaline. The present results show that in rat mesenteric small arteries noradrenaline‐induced Ca2+ sensitization is associated with an increased proportion of phosphorylated MLC. The results are consistent with a decreased MLC phosphatase activity mediated through PKC. Furthermore, while MLC phosphorylation is a requirement for force production, the results show that other factors are also involved in force regulation.

1 Simultaneous measurements of intracellular calcium concentration ([Ca 2+ ] i ) and tension were performed to clarify whether the mechanisms which cause the neuropeptide Y (NPY)-elicited contraction and potentiation of noradrenaline contractions, and the NPY inhibition of forskolin responses are linked to a single or dierent NPY receptor(s) in rat mesenteric small arteries. ] i to resting levels. NPY completely inhibited these eects. The contractile responses to NPY in arteries maximally relaxed with either sodium nitroprusside (SNP) or nifedipine were not signi®cantly higher than those evoked by the peptide at resting tension, in contrast to the contractions to NPY in forskolin-relaxed arteries. BIBP 3226 competitively antagonized the contraction to NPY in forskolin-relaxed arteries with a pA 2 of 7.92+0.29. 5 Electrical ®eld stimulation (EFS) at 8 ± 32 Hz caused large contractions in arteries relaxed with either forskolin or noradrenaline in the presence of phentolamine. These responses to EFS were inhibited by BIBP 3226. Similar EFS in resting, non-activated arteries did not produce any response. 6 The present results suggest that dierent intracellular pathways are linked to a single NPY Y 1 receptor in intact rat mesenteric small arteries, and provide little support for involvement of other postjunctional NPY receptors in the contractile responses to NPY. Neurally released NPY also seems to act through Y 1 receptors, and may serve primarily as an inhibitor of vasodilatation.