C-Jun N-terminal kinases (JNKs) can be divided into three subtypes: JNK1, JNK2, and JNK3. The MAPK kinases MKK4 and MKK7 are the kinases upstream of JNK. MKK7 activates JNK specifically [26], whereas MKK4 can activate JNK1 and p38.

MAPK may be involved in the occurrence of CVS via the following mechanisms:

PKC is a calcium/phospholipid-dependent protein kinase that regulates cell metabolism, growth, proliferation, and differentiation by catalyzing the Ser/Thr phosphorylation of many different proteins [25]. All PKC subtypes are composed of a single peptide chain, which is divided into four conserved domains, C1–C4 (in nPKC and aPKC the C2 domain is missing), and five variable regions, V1–V5 [14]. Based on their structures and activators, PKC isoforms are divided into three related families: groups A, B, and C.

The pathways of PKC activation after SAH include the following:

Increasing evidence supports essential roles for PKC in delayed CVS. After SAH, sustained DAG increase activates PKC, which maintains sustained vascular SMC [7]. PKC inhibits the activation of potassium channels in vascular SMCs. This depolarizes vascular SMCs, leading to contraction. Adhesion of extracellular collagen matrix in the cerebral arteries after SAH affects the vessel diameter. PKC can activate protein tyrosine kinase (PTK), which activates Ras. PKC may also directly activate Raf-1 and thus activate MAPK, which results in sustained vascular SMC contraction.

Rho proteins are small GTPases. Based on their primary structure, Rho proteins can be divided into at least five families: the Ras, Rho, Rab, Sarl/Arf, and Ran families. RhoA regulates the assembly of actin stress fibers, whereas Rac and Cdc42 regulate actin polymerization to form specific peripheral structures. Rho proteins also participate in the regulation of many basic cellular functions, including contraction, movement, adhesion, the maintenance of cell shape and polarity, gene transcription, and apoptosis [9].

During cell metabolism, Rho proteins act as molecular switches and exist in the GTP-bound state (active state) or GDP-bound state (inactive state). Three major proteins regulate the activation of Rho: (1) GTP exchange factor, which promotes the phosphorylation of GDP and its exchange with GTP; (2) GTPase-activating protein, which activates the endogenous GTPase activity of Rho protein, hydrolyzing GTP into GDP; and (3) GDP dissociation inhibitor, which inhibits the conversion between GDP and GTP [27].

After SAH, spasm-inducing substances in the blood can activate cell surface receptors and the downstream Rho/Rho kinase signaling pathway, resulting in increased MLC phosphorylation and SMC contraction. OxyHb and ET-1 are the two spasm-inducing substances that are well understood. In SAH, OxyHb released from self-dissolved red blood cells can cause persistent contraction of cerebral arteries in vitro. Studies suggest that activation of the OxyHb-dependent Rho/Rho kinase pathway is one step in the signaling cascade that leads to CVS [28]. ET-1 is another main cause of CVS after SAH. In the blood-containing CSF of SAH patients, ET-1 levels are elevated compared with control patients. In addition, cisternal injection of ET-1 in vivo produced CVS similar to that observed in humans. Lan et al. [15] examined rabbit basilar arteries with endothelial cells removed and found that ET-1 could significantly increase the amplitude of OxyHb-induced vasoconstriction. Importantly, the Rho kinase inhibitors Y-27632 and fasudil could reduce this effect.