Using antibodies against the annexins, Hamre et al, 1995 have shown the distribution of the annexins in the CNS. The antibodies to annexin V and VI displayed little immunoreactivity in the CNS and hence only the other three annexins were studied.
Annexin I displays the most restricted distribution o f the three proteins Annexin I, II and IV. The only structure labelled by the anti-annexin I antibody was the midline raphe o f the brainstem. Annexin I was found in the spinal cord. Annexin I immunoreactivity is also present in some non-neuronal cells such as the lens of the eye and the olfactory neuroepithelium. In contrast annexin II immunoreactivity is found in midline structures throughout the spinal cord, brain stem and mesencephalon. Annexin II was also seen in the DRG neurones of all sizes. Annexin IV is the most widely
distributed of the three annexins found throughout the spinal cord and brainstem. Annexin IV is also present in the DRG neurones.
Naciff et al (1996) carried out a study where they studied the expression of annexins in the DRG and spinal cord by using indirect immunofluorescence.
1.20.1. A nnexin I:
Annexin I is present in a high concentration in small sensory neurones throughout the DRG with a perinucleur distribution that follows a pattern similar to that shown by endoplasmic reticulum. This annexin is restricted to the soma and does not extend into the axon length either towards the central or towards the peripheral branch. Annexin I is expressed in the grey matter in the spinal cord and in neurones it is found through out the cytoplasm. It is also expressed in the oligodendrocytes ensheathing the axons.
Annexin I is found to have pharmacological activity in the CNS, as when exogenous annexin I was administered intravenously into rabbit it was found to prevent febrile reactions (Davidson et al, 1991). Intracerebral injection inhibits cytokine induced fever in rat (Carey et al, 1990). Using models of cerebral ischaemia, Relton et al,
(1991) observed increased expression of annexin in the infarcted areas, and a cerebral injection of the N-terminal region of annexin I was able to reduce the infarct size. They suggested that annexin I could be used as a therapeutic agent in the treatment of excitotoxic cell death or damage.
Annexin I is a substrate for epidermal growth factor (EGF) receptor/kinase and is phosphorylated on a tyrosine residue (Fava & Cohen, 1984). An important feature of
the EGF receptor/kinase phosphorylation of annexin I is that the reaction is of high affinity and is calcium dependent.
1.20.2. A nnexin II:
Most sensory neurones express this annexin but it is highly concentrated in the small diameter sensory neurones (Naciff et al, 1996/ Endothelial cells lining the blood vessels are also rich in annexin II. It is also expressed by Schwann cells but is absent from the axon and from the cells of the perineurium surrounding the axon bundles. Annexin II is highly expressed throughout the spinal cord by glial cells although the strongest immunoreactivity is found in the white matter. It is also expressed by oligodendrocytes surrounding the axons and by ependymal cells lining the central canal but not by astrocytes (Naciff et al, 1996).
Annexin II in the amino terminal domain contains phosphorylation sites for tyrosine kinase and protein kinase C, kinases that are important in multiple signal transduction pathways. This annexin is also able to interact through its amino terminal with p l l to form tetramers and this complexs’ calcium requirement for membrane aggregation and fusion activity is reduced. The annexin II-p ll tetramer translocates to the plasma membrane and the cytoskeleton and has been associated with the regulation of calcium dependent exocytosis (Sarafian etal, 1991).
1.20.3. A nnexin III:
This annexin is localised in most of the sensory neuronal bodies regardless of size, although it is highly concentrated in the small neurones. It is evenly distributed throughout the cytoplasm of the small neurones and in a granular pattern in the large
neurones. This annexin is also highly concentrated in endothelial cells lining the small blood vessels that surrounds the axon bundles. In contrast with I and II, annexin III is present in axons and glial cells particularly the Schwann cells. This annexin has a striking distribution along the spinal cord, being highly concentrated in astrocytes located throughout the spinal cord. There is no expression in the ependymal cells lining the canal nor the oligodendrocytes.
1.20.4. A nnexin IV:
The distribution pattern of annexin IV is very different. Peripheral glial cells are separated into two distinct groups: satellite cells and Schwann cells. Both types of cells are rich in annexin IV where it is mainly localised in the cytoplasm. The satellite cells surrounding the sensory neurones are richer in annexin IV than the neurones. In the sensory neurones this annexin is highly localised in the nucleus but absent from the nucleolus. In the cytoplasm o f the neurones this annexin is found in lesser amounts than in the nucleus and is distributed evenly in a granular pattern. Annexin IV is primarily expressed by the oligodendrocytes ensheathing the axons and is also present in ependymal cells of the central canal and in glial cells throughout the white and grey matter and the astrocytic processes that surround the axon bundles.
1.20.5. A nnexin V:
This annexin is highly expressed in most of the small sensory neurones of the DRG. In very few large neurones it is found heavily concentrated around the nucleus and follows a distribution pattern similar to the endoplasmic reticulum. It is also found at the plasma membrane. In some small sensory neurones annexin V is within the
nucleus. It is absent from the endothelial cells and glial cells. Annexin V is highly expressed by ependymal cells lining the central canal and by oligodendrocytes.
1.20.6. A nnexin VI:
Most of the sensory neurones throughout the DRG express annexin VI in relative high concentration regardless of cellular size. Some o f the large neurones have less immunoreactivity than neighbouring small neurones. In the cytoplasm this annexin is also found with a perinucleur distribution following the pattern of the endoplasmic reticulum. It is also concentrated at the plasma membrane and is also found along the axolemma of the central and peripheral branches of the sensory axons. Schwann cells ensheathing the axons contain annexins but the satellite glial cells and endothelial cells do not show annexin VI immunoreactivity. Annexin VI is concentrated at the plasma membrane of most of the large neurones in the ventral horn of the spinal cord. It is not found in the oligodendrocytes or astrocytes or in glial cells.