Rearrangement of cell types in the rat carotid body neurogenic niche induced by chronic intermittent hypoxia.

The carotid body (CB) is a prototypical acute oxygen (O2 )-sensing organ that mediates reflex hyperventilation and increased cardiac output in response to hypoxaemia. CB overactivation, secondary to the repeated stimulation produced by the recurrent episodes of intermittent hypoxia, is believed to contribute to the pathogenesis of sympathetic hyperactivity present in sleep apnoea patients. Although CB functional plasticity induced by chronic intermittent hypoxia (CIH) has been demonstrated, the underlying mechanisms are not fully elucidated. Here, we show that CIH induces a small increase in CB volume and rearrangement of cell types in the CB, characterized by a mobilization of immature quiescent neuroblasts, which enter a process of differentiation into mature, O2 -sensing and neuron-like, chemoreceptor glomus cells. Prospective isolation of individual cell classes has allowed us to show that maturation of CB neuroblasts is paralleled by an upregulation in the expression of specific glomus cell genes involved in acute O2 -sensing. CIH enhances mitochondrial responsiveness to hypoxia in maturing neuroblasts as well as in glomus cells. These data provide novel perspectives on the pathogenesis of CB-mediated sympathetic overflow that may lead to the development of new pharmacological strategies of potential applicability in sleep apnoea patients. KEY POINTS: Obstructive sleep apnoea is a frequent condition in the human population that predisposes to severe cardiovascular and metabolic alterations. Activation of the carotid body, the main arterial oxygen-sensing chemoreceptor, by repeated episodes of hypoxaemia induces exacerbation of the carotid body-mediated chemoreflex and contributes to sympathetic overflow characteristic of sleep apnoea patients. In rats, chronic intermittent hypoxaemia induces fast neurogenesis in the carotid body with rapid activation of neuroblasts, which enter a process of proliferation and maturation into O2 -sensing chemoreceptor glomus cells. Maturing carotid body neuroblasts and glomus cells exposed to chronic intermittent hypoxia upregulate genes involved in acute O2 sensing and enhance mitochondrial responsiveness to hypoxia. These findings provide novel perspectives on the pathogenesis of carotid body-mediated sympathetic hyperactivation. Pharmacological modulation of carotid body fast neurogenesis could help to ameliorate the deleterious effects of chronic intermittent hypoxaemia in sleep apnoea patients.

Dynamics and regulation of endocytotic fission pores: role of calcium and dynamin.

Although endocytosis involves the fission pore, a transient structure that produces the scission between vesicle and plasma membranes, the dimensions and dynamics of fission pores remain unclear. Here we report that the pore resistance changes proceed in three distinct phases: an initial phase where the resistance increases at 31.7 ± 2.9 GΩ/second, a slower linear phase with an overall slope of 11.7 ± 1.9 GΩ/second and a final increase in resistance more steeply (1189 ± 136 GΩ/second). The kinetics of these changes was calcium dependent. These sequential stages of the fission pore may be interpreted in terms of pore geometry as changes, first in pore diameter and then in pore length, according to which, before fission, the pore diameter consistently decreased to a value near 4 nm, whereas the pore length ranged between 20 and 300 nm. Dynamin, a mechanochemical GTPase, plays an important role in accelerating the fission event, preferentially in endocytotic vesicles of regular size, by increasing the rates of pore closure during the first and second phases of the fission pore, but hardly affected larger and longer-lived endocytotic events. These results suggest that fission pores are dynamic structures that form thin and long membrane necks regulated by intracellular calcium. Between calcium mediators, dynamin functions as a catalyst to increase the speed of single vesicle endocytosis.