Pericytes and stimulus-secretion-coupling in vivo – Peri-pulse

A number of complementary techniques and tools are used by the 4 partners:
- Developmental studies using Cre-Lox mouse models
- Cellular in vivo imaging of the pituitary gland in anesthetized mice
- Optogenetic manipulation of pericytes
- Electronic microscopy of the pituitary gland
- Characterization of cell signaling in pericytes

Main findings:
- role of specfiic vascular signaling molecules in hormone pulsatility (PloS Biol, 2014)
- specific patterning of GHRH neurons that control GH pulsatility (Sci Rep 2016)
- hormone pulsatility in response physiological demands (Adv Exp Med Biol. 2015)
- Evidence for two developmental origins of pituitary pericytes (ms in preparation)
- Evidence for an acute role of pituitary pericytes in the control of oxygen supply and hormone pulsatility (ms in preparation)

Our project highlights instrumental roles of the vasculature, namely pericytes in the control of metabolism (e.g. oxygen supply) and hormone pulsatility.
The perspectives of the project in terms of clinical relevance will be to identify potential drug targets (e.g. specific receptors) which would allow non-invasive manipulation of pericytes in health and diseases. To so we are currently exploring the transcriptomic signatures of pericytes (RNAseq from pericytes only) under various experimental conditions

1/ Giacobini et al. Plos Biology 12:e1001808, 2014
2/ Osterstock, G. et al. Sci. Rep. 6, 24394; doi: 10.1038/srep24394 (2016)
3/ Le Tissier et al. Adv Exp Med Biol. 2015;846:139-62.
Two ms in preparation

Finely tuned secretion of hormones is essential for regulating a multitude of basic body functions such as growth. Defaults in hormone rhythms are signatures of many hormonal disorders and are economically costly health care burdens (diabetes, dwarfism…). During the past 50 years, studies have been conducted to understand how hormone secretion is regulated (mostly in cells out of their in vivo context) and how hormone output can be restored in order to reverse common hormonal disorders. However, practically nothing is known about how fenestrated capillaries uptake minute amounts of hormones locally secreted by individual endocrine cells to generate hormone pulses in the bloodstream.
To elucidate the mechanisms of hormone clearance in secretory tissues, the team at Montpellier (Mollard’s group, Partner 1) has recently developed a cellular in vivo technique that has allowed imaging and quantification of the dynamics of hormone uptake by capillaries in their intact tissue environment. Implementation of this approach in living pituitary glands unveiled that GH pulse generation is not only a property of the arrangement of GH cells into a 3D network, but is also influenced by the tissue microenvironment, involving a role of the perivascular space as a gate-keeper for hormone uptake by fenestrated pituitary capillaries. Moreover, Partner 1 has worked closely during the past two years with other labs (Partner 2: R. Lovell-Badge, Stem cell & pituitary development, NIMR-MRC, London; Partner 3: V. Prévot, Neuroendocrine tissue/blood vessel cross-talks, INSERM-Lille; Partner 4: V. Goffin, GH/PRL Pathophysiology, INSERM-Paris) and has generated preliminary data which suggest that pericytes are also key players in pituitary function. Indeed, i) pericytes are closely associated with extracellular matrix (ECM) through which hormones diffuse; ii) released product is sequestered in close proximity to pericytes; iii) activation of pericytes leads to contraction and dilation of pituitary parenchyma; and iv) manipulation of pericyte activity alters GH output.
The aim of the current proposal is therefore to identify how each of these elements of the tissue microenvironment (pericytes and ECM) act individually/in concert during the build-up of GH pulses in normal mouse models as well as during acute metabolic changes to GH axis output (fasting/feeding). Specifically, we intend to explore directly in vivo and with cellular resolution the role of pericytes and associated ECM in the generation of GH pulses, namely the transfer of hormones from their site of release towards the lumen of fenestrated capillaries. To achieve this, we will take advantage of the complementary techniques and expertise (cellular in vivo imaging, optogenetic tools, organ development, endothelial cell profiling, hormone receptor characterization and manipulations…) that have already been shared by the teams of the Peri-pulse consortium to generate the preliminary results. Whilst this project might be considered ambitious due to the level of technical complexity required, the expertise and specialist equipment already exist, so there is a low risk of failure. Moreover, to address fundamental issues about the secretion of GH, one of the key players in metabolism, the project will use well characterized mouse models which are already available in-house (e.g. GH-eGFP & Wnt1-Cre mice, feeding/fasting mouse models).
Results generated by this consortium will provide new insights about the role of the tissue microenvironment in the missing link between the fast stimulus-secretion coupling events by somatotrophs and the more slowly-evolving changes in blood hormone levels. Our ANR project will also provide potentially unexpected insights into the tissue organization and function of pericytes in endocrine tissues, which could ultimately impact on our understanding and/or therapeutic management of hormone secretion-related diseases (e.g. pituitary disorders, diabetes…).