Structural and molecular analysis of arteriolar annuli in the retina: implications in diabetic and hypertensive retinopathy
- Autores: David Ramos González
- Directores de la Tesis: Jesús Ruberte París (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2014
- Idioma: español
- Tribunal Calificador de la Tesis: Rafael Simó Canonge (presid.), Maria Luísa Mendes Jorge (secret.), Hans-Peter Hammes (voc.)
- Materias:
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- Resumen
Retinal vasculature shows special characteristics in order to minimize the interference with the light path, which passes through the entire retina to reach the external segment of photoreceptors. The small size and sparse distribution of retinal capillaries, together with the high metabolic demand, makes retinal homeostasis highly dependent on blood flow regulation. Retinal blood vessels are not innervated. Thereby, the influence of autonomic nerve stimulation can be excluded. In addition, blood-retinal barrier isolates the retina from the effect of circulating hormones and neurotransmitters.
Arteriolar annuli are singular structures occurring at side-arm branching sites of retinal arterioles. These structures were defined in the mid last century by the presence of increased PAS-positive material and increased cellularity. Moreover, a recent study has evidenced the specific expression of certain genes at the arteriolar branching points. However, most of the studies dealing with arteriolar annuli are out of date and incomplete. Thus, both structure and function remain to be elucidated.
Our results have confirmed the presence of arteriolar annuli in mouse retina, appearing as a conical hypercellular structure of intensely PAS stained material. Salivary amylase digestion has shown that specific PAS stain is in some degree due to increased glycogen content in cells forming the arteriolar annuli.
Detailed morphological analyses of arteriolar annuli have evidenced three different components: endothelial, intersticial (ICs) and smooth muscle cells, showing a distinctive structural and molecular phenotype. In this regard endothelial cells show decreased expression of CD31, together with enhanced NADPH diaphorase and von Willebrand factor (vWF) expression. Thus, suggesting that annuli endothelial cells are able to induce vasodilatation and to maintain an antithrombotic milieu. Smooth muscle cells in the annuli appeared reoriented embracing the origin of the collateral arteriole. This particular disposition could indicate a sphincter-like activity by bulging annuli cells to the arteriolar lumen. In addition, ultrastuctural analysis evidenced the existence of peg-and-socket junctions between smooth muscle cells of arteriolar annuli. This result suggests a stretch-coordinated annuli contraction. Furthermore, a possible reinforcement of basement membrane was evidenced by increased expression of its main components, including collagen IV, laminin and fibronectin. A diminished colocalization of collagen IV and laminin, suggest a change in the organization of basement membrane in arteriolar annuli.
ICs have been described as a new cell population in arteriolar annuli. These cells showed features matching the gold standard ultrastructural features established for the intestinal Interstitial Cajal cells identification. In addition, annuli presumptive Interstitial Cajal cells expressed specific markers of these cells, such as Ano1 and CD44, although c-kit expression could not be observed. A distinctive pattern of distribution of F-actin filaments, together with an increased expression of beta-actin and a lack of alpha-SMA allowed further differentiation between annuli ICs and vascular smooth muscle cells. Functional studies suggest that annuli ICs perform functions of pacemarker activity and mechanotransduction.
Blood flow alteration is an early event in retinal diseases, such as diabetic and hypertensive retinopathies, which are two major causes of blindness and visual impairment worldwide. Thus, the function of arteriolar annuli and their alterations during retinopathy could be of interest in order to understand the physiopathology of vascular retinopathy.
The analyisis of arteriolar annuli in a model of type 1 diabetes (NOD mice) and in a model of hypertension (KAP transgenic mice) evidenced a decreased expression of Ano1 in annuli ICs during diabetic and hypertensive retinopathy, suggesting a loss of function of calcium-activated chloride channels. Moreover, KAP transgenic mice analysis evidenced a decreased NADPH diaphorase activity in arteriolar annuli during hypertensive retinopathy. Thus, alterations observed in the retinal ICs could induce an impaired function of arteriolar annuli driving to dysregulation of blood flow during retinopathy.
Moreover, arteriolar annuli are present in man retina. Preliminary results, as happens in mice, may suggest its alteration during retinopathy.
Taken together, our results suggest that arteriolar annuli are endowed with specific molecular, structural and functional characteristics which allow them playing a key role in the retinal blood flow regulation in health and during retinopathy.
