Frank Blaeser

An X-linked recessive syndrome of autoimmunity, allergic disregulation, and diarrhea has been recognized in several families (1-6) (Mendelian Inheritance in Man entries 304930, 304790). This syndrome, referred to herein as XLAAD (for X-linked autoimmunity-allergic disregulation syndrome), presents early in life with autoimmunity, severe allergic inflammation, secretory diarrhea, and failure to thrive (1-6). Many affected males suffer from classical type 1 diabetes mellitus that frequently presents in the immediate postnatal period or early infancy. Type 1 diabetes mellitus in XLAAD is characterized by islet cell destruction by infiltrating T cells and, in some cases, by autoantibody formation (7). Patients with XLAAD also manifest a more general predilection to autoimmune diseases including autoimmune polyendocrinopathies (especially thyroiditis), hemolytic anemia, thrombocytopenia, and enteropathy. Severe allergic inflammation in XLAAD patients is reflected by the occurrence of eczema, food allergy, elevated IgE levels, and peripheral eosinophilia. Many patients suffer from persistent secretory diarrhea, which may be caused by both food allergy-associated eosinophilic gastroenteropathy and autoimmune enteropathy. Susceptibility to recurrent staphylococcal infections has been variably described in some XLAAD patients and may reflect the wellknown association of staphylococcal infections with severe eczema. XLAAD is frequently fatal, due to unrelenting diarrhea and wasting, difficult-to-treat diabetes, and/or superimposed infections.

The Ca(2+)/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is a key effector of neuronal Ca(2+) signaling; its function was analyzed by targeted gene disruption in mice. CaMKIV/Gr-deficient mice exhibited impaired neuronal cAMP-responsive element binding protein (CREB) phosphorylation and Ca(2+)/CREB-dependent gene expression. They were also deficient in two forms of synaptic plasticity: long-term potentiation (LTP) in hippocampal CA1 neurons and a late phase of long-term depression in cerebellar Purkinje neurons. However, despite impaired LTP and CREB activation, CaMKIV/Gr-deficient mice exhibited no obvious deficits in spatial learning and memory. These results support an important role for CaMKIV/Gr in Ca(2+)-regulated neuronal gene transcription and synaptic plasticity and suggest that the contribution of other signaling pathways may spare spatial memory of CaMKIV/Gr-deficient mice.

Ca(2+) induction of a subset of cellular and viral immediate-early activation genes in lymphocytes has been previously mapped to response elements recognized by the MEF2 family of transcription factors. Here, we demonstrate that Ca(2+) activation of MEF2 response elements in T lymphocytes is mediated in synergy by two Ca(2+)/calmodulin-dependent enzymes, the phosphatase calcineurin, and the kinase type IV/Gr (CaMKIV/Gr), which promote transcription by the MEF2 family members MEF2A and MEF2D. Calcineurin up-regulates the activity of both factors by an NFAT-dependent mechanism, while CaMKIV/Gr selectively and independently activates MEF2D. These results identify MEF2 proteins as effectors of a pathway of gene induction in T lymphocytes which integrates diverse Ca(2+) activation signals and may be broadly operative in several tissues.

Ca(2+) signaling plays important roles during both axonal and dendritic growth. Yet whether and how Ca(2+) rises may trigger and contribute to the development of long-range cortical connections remains mostly unknown. Here, we demonstrate that two separate limbs of the Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK)-CaMKI cascades, CaMKK-CaMKIalpha and CaMKK-CaMKIgamma, critically coordinate axonal and dendritic morphogenesis of cortical neurons, respectively. The axon-specific morphological phenotype required a diffuse cytoplasmic localization and a strikingly alpha-isoform-specific kinase activity of CaMKI. Unexpectedly, treatment with muscimol, a GABA(A) receptor agonist, selectively stimulated elongation of axons but not of dendrites, and the CaMKK-CaMKIalpha cascade critically mediated this axonogenic effect. Consistent with these findings, during early brain development, in vivo knockdown of CaMKIalpha significantly impaired the terminal axonal extension and thereby perturbed the refinement of the interhemispheric callosal projections into the contralateral cortices. Our findings thus indicate a novel role for the GABA-driven CaMKK-CaMKIalpha cascade as a mechanism critical for accurate cortical axon pathfinding, an essential process that may contribute to fine-tuning the formation of interhemispheric connectivity during the perinatal development of the CNS.

Polymorphisms in the interleukin-4 receptor alpha chain (IL-4R alpha) have been linked to asthma incidence and severity, but a causal relationship has remained uncertain. In particular, a glutamine to arginine substitution at position 576 (Q576R) of IL-4R alpha has been associated with severe asthma, especially in African Americans. We show that mice carrying the Q576R polymorphism exhibited intense allergen-induced airway inflammation and remodeling. The Q576R polymorphism did not affect proximal signal transducer and activator of transcription (STAT) 6 activation, but synergized with STAT6 in a gene target- and tissue-specific manner to mediate heightened expression of a subset of IL-4- and IL-13-responsive genes involved in allergic inflammation. Our findings indicate that the Q576R polymorphism directly promotes asthma in carrier populations by selectively augmenting IL-4R alpha-dependent signaling.