Postsynaptic density membrane protein that indirectly regulates glutamatergic synaptic transmission through lysophosphatidic acid (LPA)-mediated signaling pathways (PubMed:19766573). Binds lysophosphatidic acid (LPA) and mediates its internalization into cells (PubMed:26671989). Could act as receptor or a transporter of this lipid at the post-synaptic membrane (PubMed:19766573, PubMed:26671989). Modulates lysophosphatidic acid (LPA) activity in neuron axonal outgrowth during development by attenuating phospholipid-induced axon collapse (By similarity). Brain-specific, it is exclusively expressed in neurons (at protein level). O-glycosylated. Probably at Ser-347. Knockout mice lacking Plppr4 are viable but show a severe alteration of synaptic transmission leading to juvenile epileptic seizures (PubMed:19766573). Excitatory transmission in CA1 pyramidal neurons is significantly increased (PubMed:19766573). It is associated with transiently reduced weight during development, a reduction in brain size and higher mortality 3 to 4 weeks after birth (PubMed:19766573). Heterozygous knockout mice, show loss of somatosensory filter function and altered resilience during stress-related behaviors (PubMed:26671989). Belongs to the PA-phosphatase related phosphoesterase family. Originally described as a 2-lysophosphatidate/LPA phosphatase (PubMed:12730698). However, following studies suggested it does not have such activity or only a residual one (PubMed:19766573). This is further supported by the fact that the phosphatase sequence motifs as well as the His residue acting as a nucleophile in active phosphatases of the PA-phosphatase related phosphoesterase family are not conserved (PubMed:19766573).