Tuberous sclerosis in two sibs of normal parents

RIPK1 Mediates TNF-Induced Intestinal Crypt Apoptosis During Chronic NF-κB Activation

BACKGROUND AND AIMS

Tumor necrosis factor (TNF) is a major pathogenic effector and a therapeutic target in inflammatory bowel disease (IBD), yet the basis for TNF-induced intestinal epithelial cell (IEC) death is unknown, because TNF does not kill normal IECs. Here, we investigated how chronic nuclear factor (NF)- κB activation, which occurs in human IBD, promotes TNF-dependent IEC death in mice.

METHODS

Human IBD specimens were stained for p65 and cleaved caspase-3. C57BL/6 mice with constitutively active IKKβ in IEC (Ikkβ(EE)^IEC), Ripk1^D138N/D138N knockin mice, and Ripk3^-/- mice were injected with TNF or lipopolysaccharide. Enteroids were also isolated from these mice and challenged with TNF with or without RIPK1 and RIPK3 inhibitors or butylated hydroxyanisole. Ripoptosome-mediated caspase-8 activation was assessed by immunoprecipitation.

RESULTS

NF-κB activation in human IBD correlated with appearance of cleaved caspase-3. Congruently, unlike normal mouse IECs that are TNF-resistant, IECs in Ikkβ(EE)^IEC mice and enteroids were susceptible to TNF-dependent apoptosis, which depended on the protein kinase function of RIPK1. Constitutively active IKKβ facilitated ripoptosome formation, a RIPK1 signaling complex that mediates caspase-8 activation by TNF. Butylated hydroxyanisole treatment and RIPK1 inhibitors attenuated TNF-induced and ripoptosome-mediated caspase-8 activation and IEC death in vitro and in vivo.

CONCLUSIONS

Contrary to common expectations, chronic NF-κB activation induced intestinal crypt apoptosis after TNF stimulation, resulting in severe mucosal erosion. RIPK1 kinase inhibitors selectively inhibited TNF destructive properties while preserving its survival and proliferative properties, which do not require RIPK1 kinase activity. RIPK1 kinase inhibition could be a potential treatment for IBD.

High rate of mosaicism in tuberous sclerosis complex

Six families with mosaicism are identified in a series of 62 unrelated families with a mutation in one of the two tuberous sclerosis complex (TSC) genes, TSC1 or TSC2. In five families, somatic mosaicism was present in a mildly affected parent of an index patient. In one family with clinically unaffected parents, gonadal mosaicism was detected after TSC was found in three children. The detection of mosaicism has consequences for genetic counseling of the families involved, as changed risks apply to individuals with mosaicism, both siblings and parents. Clinical investigation of parents of patients with seemingly sporadic mutations is essential to determine their residual chance of gonadal and/or somatic mosaicism, unless a mosaic pattern is detected in the index patient, proving a de novo event. In our data set, the exclusion of signs of TSC in the parents of a patient with TSC reduced the chance of one of the parents to be a (mosaic) mutation carrier from 10% to 2%. In the five families with somatic mosaicism, the parent was given the diagnosis after the diagnosis was made in the child.

Renal involvement in tuberous sclerosis complex: a retrospective survey

In a retrospective survey performed in Germany and Switzerland, 207 patients (ranging in age from newborn to 70 years) were evaluated in order to establish the frequency, prognosis and diagnostic awareness of kidney involvement in the tuberous sclerosis complex. Renal manifestations were observed in 48% of patients: renal cysts (33 patients), renal angiomyolipoma (AML) (30 patients), a combination of both (8 patients), renal cell carcinoma (3 patients), life-threatening events such as haemorrhage (4 patients), hypertensive crisis (2 patients) and chronic renal failure (10 patients) were also documented. The diagnostic imaging techniques of ultrasonography, intravenous urography, computed tomography and magnetic resonance imaging (MRI) are important but do not always yield definitive information. Differentiation between AML and cysts can be achieved using special MRI techniques (RARE). The potential for renal involvement should be monitored in all patients with the tuberous sclerosis complex.

Variability of expression in tuberous sclerosis

We present three families in whom a diagnosis of tuberous sclerosis is difficult to secure and we review published reports about similar cases. Tuberous sclerosis has been reported to affect as many as 1 in 9400 subjects in the population. The manifestations of this disease vary not only between but also within families. Currently no reliable method of prenatal diagnosis is available. For these reasons, subjects known to be at 50% risk should be assessed scrupulously to clarify their status. These cases illustrate the difficulties in the clinical diagnosis of tuberous sclerosis and further reinforce the need for a molecular method of determining whether an at risk subject has the disease.

Tuberous sclerosis complex: genetic aspects

Much has been learned about tuberous sclerosis complex (TSC) since it was described at the end of the nineteenth century. TSC was recognized to be a genetic disease with autosomal dominant inheritance in the early twentieth century. The prevalence in the general population is at least 1 in 10,000 with two-thirds of cases occurring sporadically and one-third of cases being familial. The disease exhibits variable expression which may cause mildly affected individuals to be undiagnosed. Because the aberrant or missing proteins which result in TSC have eluded investigators, a positional cloning approach has been pursued to find the mutated genes. Genetic linkages have been reported to chromosomes 9, 11, and 12. There is definite evidence for a TSC-causing locus on chromosome 9 which is thought to account for between one-third and one-half of all familial cases. Investigators have narrowed the location on chromosome 9 to approximately two megabases of physical distance. There is some evidence for a locus on chromosome 11 which probably accounts only for a small percentage of familial cases. The locus proposed on chromosome 12 was reported by a single group and has not been confirmed by other research groups. Evidence for genetic heterogeneity is abundant. There is definitely a TSC-causing locus on chromosome 9q (TSC-1) and there is at least one additional locus, maybe more than one. As the molecular basis of TSC unfolds, new insight will be gained about the protean nature of the disorder and the genetic heterogeneity.