Jacques Pantel

Syndromic Short Stature in Patients with a Germline Mutation in the LIM Homeobox LHX4

Studies of genetically engineered flies and mice have revealed the role that orthologs of the human LIM homeobox LHX4 have in the control of motor-neuron-identity assignment and in pituitary development. Remarkably, these mouse strains, which bear a targeted modification of Lhx4 in the heterozygous state, are asymptomatic, whereas homozygous animals die shortly after birth. Nevertheless, we have isolated the human LHX4 gene, as well as the corresponding cDNA sequence, to test whether it could be involved in developmental defects of the human pituitary region. LHX4, which encodes a protein 99% identical to its murine counterpart, consists of six coding exons and spans >45 kb of the q25 region of chromosome 1. We report a family with an LHX4 germline splice-site mutation that results in a disease phenotype characterized by short stature and by pituitary and hindbrain (i.e., cerebellar) defects in combination with abnormalities of the sella turcica of the central skull base. This intronic mutation, which segregates in a dominant and fully penetrant manner over three generations, abolishes normal LHX4 splicing and activates two exonic cryptic splice sites, thereby predicting two different proteins deleted in their homeodomain sequence. These findings, which elucidate the molecular basis of a complex Mendelian disorder, reveal the fundamental pleiotropic role played by a single factor that tightly coordinates brain development and skull shaping during head morphogenesis.

Loss of constitutive activity of the growth hormone secretagogue receptor in familial short stature

The growth hormone (GH) secretagogue receptor (GHSR) was cloned as the target of a family of synthetic molecules endowed with GH release properties. As shown recently through in vitro means, this receptor displays a constitutive activity whose clinical relevance is unknown. Although pharmacological studies have demonstrated that its endogenous ligand--ghrelin--stimulates, through the GHSR, GH secretion and appetite, the physiological importance of the GHSR-dependent pathways remains an open question that gives rise to much controversy. We report the identification of a GHSR missense mutation that segregates with short stature within 2 unrelated families. This mutation, which results in decreased cell-surface expression of the receptor, selectively impairs the constitutive activity of the GHSR, while preserving its ability to respond to ghrelin. This first description, to our knowledge, of a functionally significant GHSR mutation, which unveils the critical importance of the GHSR-associated constitutive activity, discloses an unusual pathogenic mechanism of growth failure in humans.

Recessive Isolated Growth Hormone Deficiency and Mutations in the Ghrelin Receptor

CONTEXT Both GH releasing- and orexigenic properties of the gut-to-brain hormone ghrelin are mediated by the GH secretagogue receptor (GHSR). Recently in several patients, a missense mutation (p.A204E) resulting in a complete loss of GHSR constitutive activity has been implicated in short stature with dominant transmission. OBJECTIVE The objective of the study was to describe the phenotype associated with partial isolated GH deficiency of a young patient born to unrelated parents and identify the molecular basis of his disease. RESULTS The growth delay (-3.0 sd) was associated with recurrent episodes of abdominal pain, vomiting, ketosis, hypoglycemia, and a low body mass index. GHSR sequencing revealed that the patient was compound heterozygous for two new defects: 1) an early occurring transition predicting a premature stop codon (c.6G>A, p.W2X) inherited from his unaffected father, therefore strongly arguing against haploinsufficiency as a disease mechanism, and 2) a missense mutation (c.709A>T, p.R237W) inherited from his healthy mother, involving an evolutionary invariant residue from the third intracellular loop. In vitro experiments showed that the p.R237W mutation would result in a partial loss of constitutive activity of the receptor, whereas both its ability to respond to ghrelin and its cell surface expression are preserved. CONCLUSION These data, which describe the first case of recessive partial isolated GH deficiency due to GHSR mutations and emphasize the physiological importance of the GHSR in somatic growth, are discussed in light of the dominantly expressed p.A204E mutation.

Enhanced responsiveness of Ghsr Q343X rats to ghrelin results in enhanced adiposity without increased appetite

Ghrelin promotes weight gain in the form of fat without increasing appetite. The fattening effect of ghrelin Because secretion of the peptide hormone ghrelin by the stomach is thought to enhance food intake, there is interest in targeting ghrelin or its receptor GHSR to suppress appetite. However, genetic ablation of the genes encoding ghrelin, GHSR, or the enzyme that activates ghrelin does not alter food intake in mice. Chebani et al. found that cells with a truncated form of GHSR had larger responses to ghrelin than cells with the full-length GHSR. Rats bearing this mutant form of GHSR were more sensitive to injected ghrelin and gained more body weight as fat without eating more food than their normal counterparts. Thus, ghrelin promotes the expansion of adipose tissue without affecting appetite. Furthermore, these rats with the mutant GHSR could be used to identify anti-obesity treatments. The ability of the gut hormone ghrelin to promote positive energy balance is mediated by the growth hormone secretagogue receptor (GHSR). GHSR is a G protein–coupled receptor (GPCR) that is found centrally and peripherally and that can signal in a ligand-independent manner basally or when heterodimerized with other GPCRs. However, current Ghsr knockout models cannot dissect ghrelin-dependent and ghrelin-independent signaling, precluding assessment of the physiological importance of these signaling pathways. An animal model carrying a Ghsr mutation that preserves GHSR cell surface abundance, but selectively alters GHSR signaling, would be a useful tool to decipher GHSR signaling in vivo. We used rats with the GhsrQ343X mutation (GhsrM/M), which is predicted to delete the distal part of the GHSR carboxyl-terminal tail, a domain critical for the signal termination processes of receptor internalization and β-arrestin recruitment. In cells, the GHSR-Q343X mutant showed enhanced ligand-induced G protein–dependent signaling and blunted activity of processes involved in GPCR signal termination. GhsrM/M rats displayed enhanced responses to submaximal doses of ghrelin or GHSR agonist. Moreover, GhsrM/M rats had a more stable body weight under caloric restriction, a condition that increases endogenous ghrelin tone, whereas under standard housing conditions, GhsrM/M rats showed increased body weight and adiposity and reduced glucose tolerance. Overall, our data stress the physiological role of the distal domain of GHSR carboxyl terminus as a suppressor of ghrelin sensitivity, and we propose using the GhsrM/M rat as a physiological model of gain of function in Ghsr to identify treatments for obesity-related conditions.

Molecular screening of a large cohort of Moroccan patients with congenital hypopituitarism

Congenital hypopituitarism is a rare disease which, for most patients, has no identified molecular cause. We aimed to document the molecular basis of growth retardation in a Moroccan cohort.

Targeting the cis-dimerization of LINGO-1 with low MW compounds affects its downstream signalling

The transmembrane protein LINGO‐1 is a negative regulator in the nervous system mainly affecting axonal regeneration, neuronal survival, oligodendrocyte differentiation and myelination. However, the molecular mechanisms regulating its functions are poorly understood. In the present study, we investigated the formation and the role of LINGO‐1 cis‐dimers in the regulation of its biological activity.